Device having a measuring apparatus for measuring forces and/or loads

Abstract

A component of a machine. The component has a measuring fixture for measuring forces and at least one metallic, magnetic portion. The measuring fixture includes at least one field-generating member for producing an electromagnetic alternating field and at least one detection member for detecting changes of the magnetic field produced. The field-generating member and the detection members are arranged on the metallic, magnetic portion and are designed to interact with the metallic, magnetic portion in such manner that by way of the measuring fixture, as a function of measurement signals from the detection member, forces acting on and/or deformations of the component can be detected.

Claims

1. A chassis component (1) of a machine, wherein the chassis component has a curved outer surface, the chassis component comprising: at least one metallic, magnetic portion of the chassis component (1b), and a measuring fixture (1a) for measuring forces, and the measuring fixture (1a) comprising a pair of partially annular shaped field-generators (3; 3a, b), each having a first end and a second end for producing an electromagnetic alternating field and a pair of detectors (5; 5a, b) for detecting changes of the magnetic field produced, the first end of each of the pair of partially annular shaped field-generators (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a first gap and the second end of each of the pair of partially annular shaped field-generators (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a second gap, and each of the pair of partially annular shaped field-generators (3; 3a, b), the first gap, the second gap, and a portion of the curved surface of the chassis component defining an internal space and a respective one of the pair of detectors (5; 5a, b) being completely located in the respective internal space, the pair of field-generators (3; 3a, b) and the respective pair of detectors (5; 5a, b) being arranged adjacent to, but not in direct contact with, the curved surface of the metallic, magnetic portion of the chassis component (1b) and designed to interact with the metallic, magnetic portion of the chassis component (1b) in such a manner that by way of the measuring fixture (1a), as a function of measurement signals from the pair of detectors (5; 5a, b), at least one of a force acting on and deformation of the chassis component (1) is detectable.

2. The chassis component according to claim 1, wherein the machine is a wind power generator, and the chassis component is either a shaft or a rotor blade of the wind power generator that at least one of moves and is loaded during operation.

3. The chassis component (1) according to claim 1, wherein the machine is in a vehicle and the chassis component (1) is in the form of one of the following components: a damper element, a piston rod of a damper element; a control arm; a connecting strut (1c); a hinged support; a stabilizer; a steering element, a steering rod, a steering column and a track rod.

4. The chassis component (1) according to claim 3, wherein at least one of the pair of field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) is in the form of coils.

5. The chassis component (1) according to claim 3, wherein the pair of field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) are arranged in fixed positions in a housing (2), the housing (2) is arranged in a fixed position on the chassis component (1), and the pair of field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) are immobilized within the housing (2) by a hardened cast mass (2c).

6. The chassis component (1) according to claim 5, wherein the chassis component (1) has a fixing structure (6c) for the housing (2), the fixing structure (6c) is formed integrally with the chassis component (1) in the form of an aperture in the chassis component (1), and the fixing structure (6c) is formed by local deformation of the chassis component (1).

7. The chassis component (1) according to claim 3, wherein the chassis component (1) has at least one weld seam (1f) and at least one of the pair of field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) is arranged on the chassis component (1) and is spaced from the weld seam (1f) by a distance of between approximately 30 mm and approximately 40 mm.

8. The chassis component (1) according to claim 3, wherein the pair of detectors (5; 5a, b) and the pair of field-generators (3; 3a, b) are substantially arranged in a plane and a neutral fiber (NF) of the chassis component (1) lies in the same plane.

9. The chassis component (1) according to claim 8, wherein the plane is at least approximately perpendicular to a main bending direction of the vehicle component.

10. The chassis component (1) according to claim 1, wherein the measuring fixture (1a) comprises the pair of field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) and an arrangement of the pair of field-generators (3a, b) and the pair of detectors (5a, b), relative to one another, on opposite sides of the chassis component (1) is the same.

11. A chassis component (1) of a machine, wherein the chassis component has a curved outer surface, the chassis component comprising: at least one metallic, magnetic portion of the chassis component (1b), and a measuring fixture (1a) for measuring forces, and the measuring fixture (1a) comprising at least one partially annular shaped field-generator (3; 3a, b) having a first end and a second end for producing an electromagnetic alternating field and at least one detector (5; 5a, b) for detecting changes of the magnetic field produced, the first end of the at least one partially annular shaped field-generator (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a first gap and the second end of the at least one partially annular shaped field-generator (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a second gap, the at least one partially annular shaped field-generator (3; 3a, b), the first gap, the second gap, and a portion of the curved surface of the chassis component defining an internal space and the at least one detector (5; 5a, b) being located completely within the internal space, the at least one partially annular shaped field-generator (3; 3a, b) and the at least one detector (5; 5a, b) being arranged adjacent to, but not in direct tact with, the curved surface of the metallic, magnetic portion of the chassis component (1b) and designed to interact with the metallic, magnetic portion of the chassis component (1b) in such a manner that by way of the measuring fixture (1a), as a function of measurement signals from the at least one detector (5; 5a, b), at least one of a force acting on and deformation of the chassis component (1) is detectable, wherein the at least one partially annular shaped field-generator (3; 3a, b) comprises a pair of partially annular shaped field-generators (3; 3a, b) and the at least one detector (5; 5a, b) comprises a pair of detectors (5; 5a, b), the chassis component (1) has at least one weld seam (1f) and at least one of the pair of at least one partially annular shaped field-generators (3; 3a, b) and the pair of detectors (5; 5a, b) is arranged on the chassis component (1) and is spaced from the weld seam (1f) by a distance of between approximately 30 mm and approximately 40 mm.

12. A chassis component (1) of a machine, the chassis component comprising: at least one metallic, magnetic portion of the chassis component (1b), wherein the chassis component has a curved outer surface, and a measuring fixture (1a) for measuring forces, and the measuring fixture (1a) comprising at least one partially annular shaped field-generator (3; 3a, b) having a first end and a second end for producing an electromagnetic alternating field and at least one detector (5; 5a, b) for detecting changes of the magnetic field produced, the first end of the at least one partially annular shaped field-generator (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a first gap and the second end of the at least one partially annular shaped field-generator (3; 3a, b) being spaced apart from the curved outer surface of the chassis component by a second gap, the at least one partially annular shaped field-generator (3; 3a, b), the first gap, the second gap, and a portion of the curved surface of the at least one metallic, magnetic portion of the chassis component (1b) together defining a space and the at least one detector (5; 5a, b) being located completely within the space, the at least one partially annular shaped field-generator (3; 3a, b) and the at least one detector (5; 5a, b) being arranged adjacent to, but not in direct contact with, the curved surface of the metallic, magnetic portion of the chassis component (1b) and designed to interact with the metallic, magnetic portion of the chassis component (1b) in such a manner that by way of the measuring fixture (1a), as a function of measurement signals from the at least one detector (5; 5a, b), at least one of a force acting on and deformation of the chassis component (1) is detectable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, further advantages and characteristics of the present invention are explained with reference to example embodiments. The figures show:

(2) FIG. 1: A perspective view of a chassis component according to the invention with a measuring fixture and the housing that encloses the measuring fixture;

(3) FIG. 2: The chassis component according to the invention shown in FIG. 1, without the housing;

(4) FIG. 3: A view of the chassis component with its measuring fixture shown in FIG. 2, as seen from above;

(5) FIG. 4: A sectioned view along the line 4-4 in FIG. 3;

(6) FIG. 5: An exploded view of a chassis component according to the invention with the measuring fixture and its housing;

(7) FIG. 6: A slightly rotated view of the exploded representation in FIG. 5;

(8) FIG. 7: A view of the object in FIGS. 5 and 6 after assembly;

(9) FIGS. 8a, 8b: Front and side views, respectively, of an example of a sensor structure according to the invention;

(10) FIG. 9: An example of an individual sensor element according to the invention;

(11) FIG. 10: Another example of a sensor element according to the invention;

(12) FIG. 11: Yet a further example of a sensor element according to the invention:

(13) FIGS. 12a, 12b: First and second sensor designs showing two possible sensor element orientations relative to the test object according to the invention;

(14) FIGS. 13a, 13b: First and second sensor designs showing only one sensor element according to the invention;

(15) FIGS. 14a, 14b, 14c: A side view and first and second front views, respectively, of another example of a sensor element according to the invention;

(16) FIG. 15: A further example of a sensor element according to the invention;

(17) FIGS. 16a, 16b: Side and front views, respectively, of a sensor element having sensor hardware positioned close to the test object;

(18) FIGS. 17a, 17b, 17c: A side view and first and second front views, respectively, of yet another example of a sensor element according to the invention;

(19) FIGS. 18a, 18b, 18c: Side views of sensor elements of which the magnetic pole surfaces are adapted for shafts of different diameters;

(20) FIGS. 19a, 19b, 19c: Side views of sensor elements illustrating arc characteristic means according to the invention;

(21) FIGS. 20a, 20b: First and second views of sensor elements illustrating changes in the structure of sensor hardware for shafts of different diameters;

(22) FIG. 21: Another example of a sensor element according to the invention;

(23) FIGS. 22a, 22b, 22c: A side view and first and second front views of a sensor element showing a magnetic flux concentrator at different inclinations;

(24) FIG. 23: A side view of a magnetic field concentrator and three alternative designs thereof; and

(25) FIGS. 24a, 24b: Side views of first and second, respectively, variations of a magnetic flux concentrator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(26) FIG. 1 shows a chassis component 1 according to the invention, which is in the form of a connecting strut 1c, for example a hinged support, and which has at its ends ball bearings 1d, 1e or corresponding bearing sleeves. At the points indexed 1f the connecting strut 1c is joined to the ball bearings 1d, 1e in a material-cohesive manner by means of a weld seam, although this cannot be explicitly seen in the figures. On the chassis component 1 is arranged a housing 2, preferably made of plastic. In the housing 2 is arranged, in the manner described in the introduction and in the annex, a measuring fixture (not visible in FIG. 1), which will be described in more detail below with reference to the other figures. The housing 2 protects the parts of the measuring fixture and secures them in position relative to the connecting strut 1c and the component 1. Cables 4 emerge from the housing 2 to carry the measurement signals emitted. The cable connections lead, for example, to the control unit of a stabilizer or to an electronic fault memory of the vehicle. In addition, the cables 4 contain leads for controlling and for supplying electricity to the measuring fixture.

(27) In the housing 2 are arranged field-generating means and detection means of the measuring fixture mentioned several times already (not shown). The arrangement of the means is explained with reference to the figures below.

(28) FIG. 2 shows the chassis component 1 of FIG. 1, but without the housing 2, so that the measuring fixture indexed 1a in FIG. 2 can be seen. The measuring fixture 1a comprises field-generating means 3, or more precisely: a first field-generating means 3a and a second field-generating means 3b, detection means 5 (of which only one is visible) and electronic means 7 for the further processing (evaluation, storage, etc.) of the measurement signals produced by the measuring fixture 1a. The cables 4 already mentioned are connected to the electronic means 7. Besides the transmission of measurement or evaluation signals, the cables 4 also serve in particular for the supply of energy to the measuring fixture as a whole, including the actual sensors (indexed 3 and 5) and the associated electronics 7.

(29) The field-generating and detection means 3, 5 are located in a metallic, magnetizable portion 1b of the component 1 or connecting strut 1c. However, it is within the scope of the invention to make the entire connecting strut 1c from the metallic, magnetizable material. The portion 1b then includes the whole of the connecting strut 1c.

(30) FIG. 3 shows the chassis component 1 in FIG. 2 as viewed from above. Relative to the (right-hand) end of the connection strut 1c, the two field-generating means 3a, b and the detection means (not visible in this case) are arranged on the chassis component 1 at the same level and the same distance away from the connecting strut 1c. This gives a symmetrical design of the measuring fixture 1a relative to the mid-plane M of the chassis component 1 or connecting strut 1c.

(31) As shown in FIG. 3 the measuring fixture 1a is a distance x away from the weld seam 1f in the area of the ball joint 1e or the bearing sleeve concerned. The distance x denotes in particular the distance from the mid-point of the detection coils (see for example FIG. 4) to the weld seam 1f. A value of x=35 mm±1 mm has been found particularly appropriate in practice.

(32) FIG. 4 shows a sectioned view through the chassis component 1 taken along the line 4-4 in FIG. 3. The connecting strut 1c is at least partially enclosed by two field-generating means 3a, b of partial annular overall shape. Each partially annular-shaped element 3aa, 3ba constitutes a field concentrator which acts in the manner of a known coil core, as explained in more detail in the annex. The actual field-generating or energizer coil arranged respectively around the field concentrator 3aa, 3ba is not shown in FIG. 4 to make the illustration easier to understand. Between the field-generating means 3a, b and the connecting strut 1c are arranged two detection means 5a, b, one detection means (measurement coil) 5a being arranged on the side of the first field-generating means 3a and the other detection means (measurement coil) 5b on the side of the second field-generating means 3b. Furthermore, the neutral fiber of the chassis component defined earlier in the description is shown symbolically in FIG. 4, indexed NF. This is the notional plane in the connecting strut 1c which, when the strut is loaded by bending as indicated by the double arrow BR, essentially undergoes no extension or compression as happens above and below the neutral fiber NF (on the right and left in FIG. 4).

(33) The field-generating means and detection means 3a, b; 5a, b are arranged in the same way on the two sides of the connecting strut 1c, in such manner that the (notional) centers of each individual means lie on a line. This gives the symmetrical design of the measuring fixture 1a, already mentioned.

(34) The electric connections also visible particularly in FIG. 4 between the parts of the measuring fixture 1a and the electronic unit 7 are not explicitly shown, for the sake of simplicity.

(35) The field-generating and detection means 3, 5 shown in FIG. 4 are arranged offset relative to the main bending direction of the strut 1c denoted, as an example, by the arrow BR. Investigations by the applicant have shown that such an arrangement of the measuring fixture 1a gives particularly advantageous measurement results.

(36) FIG. 5 shows an exploded view of the chassis component 1 according to the invention, with a housing 2 consisting of an upper housing half 2a and the lower housing half 2b. In the two housing halves 2a, 2b corresponding apertures 6a are provided in order to enable the housing halves to be joined around the strut 1c by means of fasteners 6b, preferably in the form of screws or screw-bolts, to form the complete housing 2. The inside of the housing is filled with a (plastic) cast mass 2c which surrounds the parts of the measuring fixture protectively, including the electronic unit, and ensures that their relative positioning is maintained.

(37) FIG. 6 shows a slightly rotated view of the chassis component 1 according to the invention as represented in FIG. 5. For completeness, let it be pointed out that the lower housing half 2b has apertures 6a which are in part larger than those in the upper housing half 2a, in order to enable complete countersinking of the fastening means 6b. Furthermore, on the chassis component 1 or strut 1c a fixing structure 6c is provided on both sides in the form of a recess for the location of the housing 2. Correspondingly, on its upper half 2a and on its lower half 2b the housing 2 has projections 2d which are designed to fit into the recesses 6c in the strut 1c, in order to enable the measuring fixture to be fixed exactly at the required (measurement) position on the strut 1c.

(38) FIG. 7 shows the elements of the two exploded views in FIGS. 5 and 6 in the assembled condition, with the fastening means 6b countersunk in the apertures 6a.

Annex: Device Having a Measuring Apparatus for Measuring Forces and/or Loads

(39) Below, preferred features of a measurement method and design details of the measuring fixture (sensor) will be described. This description is based on a parallel patent application by Polyresearch AG with the same timing.

(40) In what follows, and without placing any limit on its generality, the measuring fixture will be referred to as the sensor or bending sensor. Likewise, without placing any limit on generality, the field-generating means will be referred to as the inductor, the magnetic field-generating coil or the primary coil and the detection means as the magnetic sensor element.

(41) In all the figures the same indexes denote the same, or functionally equivalent elements.

(42) Active Bending Sensor

(43) For the measurement of bending forces, in industry and in research and development laboratories strain gauges are used in most cases. There are only a few alternative sensor systems available, that can provide appropriate bending sensor measuring performance and which are suitable for the environmental conditions in which such sensors are intended to be used. In general, however, such systems are too expensive for mass production (which is typical in the automotive industry, in the industrial sector and in the consumer sector).

(44) No inexpensive bending sensor systems are available for applications in which the test object (such as a transmission shaft) rotates during its use. For that, an inexpensive and no-contact measurement technique is required. The following description relates to a design of a mechanical force sensor that works on magnetic principles, which can detect and quantify mechanical forces in ferromagnetic objects such as a transmission shaft, a screwdriver shank, torque wrenches or a drilling machine shaft.

(45) The unique features of this “active” sensor system are as follows: A genuinely no-contact sensor principle Operates on magnetic principles Insensitive to magnetic fields already present or stored in the test object The test object does not in any way need to be pretreated (the “active” bending sensor module is held close to the test object and functions immediately without further preparation measures) The sensor's performance cannot deteriorate over time, since an active sensor principle is being used Insensitive to torques (for measurements in differential operating mode I) Sensitive to a bending force in only one axis (no cross-induction between bending forces in the X and Y axes) Functions on test objects that are stationary or rotating at any speed Insensitive to light, dust, mechanical shocks of any type, water, humidity, oil, etc. Functions with any metallic test object material so long as it attracts a magnet Tolerates varying air gaps/distances between the test object and the sensor module No upper limit for test object size (for example shaft diameter) Operates in a temperature range from −50° C. to over +210° C.

(46) What is the difference from other sensor technologies?

(47) 1. This sensor does NOT need to be physically in contact with the test object. Even with a gap of a couple of millimeters (between the sensor and the test object) it still functions properly. Thus, the sensor functions quite independently of the condition of the test object's surface (coated, painted, dusty, etc), which is ideal for measuring on building sites, bridges, cranes, supporting frames, etc.

(48) 2. The sensor functions with ANY metallic material, so long as the magnetic properties of the material suffice to attract/hold a permanent magnet (does not apply in the case of sintered materials, which are too brittle when bending forces are imposed).

(49) 3. The test object does not need to be modified in any way. The test object is not processed in any way.

(50) Sensor structure

(51) The sensor consists of two main modules: the actual sensor element (made using passive electronic components), and the sensor's electronic unit

(52) Both modules can be accommodated together in the same housing, but they can also be arranged separately from one another and only connected to one another by a number of cables. The length of the cables is restricted by a natural limit (in the range of 2 meters or more).

(53) An example of the structure is shown in FIGS. 8a and 8b, with a side view in FIG. 8a and a front view in FIG. 8b. A test object A1 is shown.

(54) The representation in FIGS. 8a and 8b is only one of several possible structures of the sensor element. The main components are shown in the drawing. These are: Magnetic flux concentrator A2 Magnetic field-generating coil (inductor) or primary coil A3 Magnetic sensor element (which can be any type of magnetic field sensor device: coil, Hall effect, MR, GMR, etc.) A4 Optionally: signal feedback coil (inductor) or secondary coil A5.

(55) A complete and individual sensor element preferably consists of all the components shown in FIG. 9. The feedback coil A5 (L.sub.S—secondary inductor) can optionally be included and is only needed if any distance changes (between the test object and the sensor module) have to be compensated automatically. In addition a current supply A6 and the sensor's electronic unit A7 are shown.

(56) Important: The function of the feedback coil can be used when the field-generating coil is operated with an alternating-voltage control signal.

(57) The “optional” feedback coil (L.sub.S) is used to detect and measure the distance (or gap) between the sensor element and the surface of the test object. The signal measured by this coil is used for compensating the undesired signal amplitude modulation which occurs when the distance between the test subject and the sensor element changes continually. In applications in which the distance does not change, no feedback coil is needed.

(58) FIG. 10 shows the following: the field-generating coil (LP—primary inductor) and the feedback coil (LS—secondary inductor) are arranged on the same flux concentrator. Signals produced by the field-generating coil can be picked up and measured by the feedback coil. The signal transfer function is influenced by the distance between the flux concentrator and the surface of the test object. The smaller the air gap between the two poles of the flux concentrator ends and the surface of the test object, the more efficient is the magnetic transfer between the primary and secondary coils. This relationship is not strictly proportional and has to be linearized by the sensor's electronic system.

(59) FIG. 11 shows the following: a change of the distance between the flux concentrator and the test object results in a change of the amplitude of the signal measured by the feedback coil L.sub.S. The signal amplitude information from the field-generating coil LP and the feedback coil L.sub.S makes it possible for an amplifier with variable amplification to correct the otherwise varying bending signal amplitude. Important in this: it may be necessary first to linearize the feedback coil signal before it is passed on to the amplifier with variable amplification. The components/functional blocks shown are: a signal generator A7, a filter and power driver A8, a filter and gain A9 and a variable-gain amplifier A10.

(60) Measuring in the Differential Operating Mode

(61) To distinguish between the relevant bending force and other mechanical forces (such as torques), two sensor elements of identical make-up are arranged symmetrically on the two sides of the test object. By subtracting the measured signals one from the other the potentially existing torques cancel out, leaving behind the relevant bending forces.

(62) The two signals (one from each individual sensor element) can be processed mathematically in various ways: Connecting the magnetic field sensor coils to one another in the reverse sequence (series connections such that the measured signals are subtracted one from the other, without the use of active electronic means), Feeding the individual and processed measurement signals into a summation circuit working in analog mode, to subtract the signals one from the other. Using a digital processing system (such as a microprocessor) to carry out the mathematical signal processing. This is the most flexible system.

(63) Important here: if the method proposed first is chosen (connecting the positive magnetic field sensor coils in series), great care must be taken to ensure that the signal amplitudes and existing opposite signal offsets are well matched to one another. Otherwise, the resulting signal will contain cross-induction and is then distorted (compared with the relevant output signal).

(64) Sensor Orientation Relative to the Test Object

(65) Two fundamentally different sensor designs give good measurement results, here called “Design 1” and Design 2″ (owing to similarities with other objects when considering the sectioned views pictured below: “Glider” and “Monkey”, respectively FIG. 12a and FIG. 12b.

(66) FIGS. 12a and 12b show the following: two of the possible sensor element orientations relative to the test object. The dark-colored parts symbolize the magnetic field sensor device, which can be either an inductor with a core, a Hall effect sensor, MR, GMR, or any other magnetic field device which is suitable for the desired measurement range. The orientation of the magnetic field sensor device relative to the magnetic field lines (between the two poles of the flux concentrator) is critical, as explained in another section of this description.

(67) What happens if the differential operating mode is not used?

(68) Naturally, it is also possible to use a single sensor cell for measuring the desired mechanical forces. The use of only one sensor cell reduces costs sill farther and makes the sensor much smaller. In that case, however, it is no longer possible to distinguish between the bending forces applied and the other mechanical forces potentially present, such as torques and bending in other axes. Thus, the use of a design with a single sensor cell means that the sensor module picks up several different mechanical forces at the same time, without it being possible to distinguish between them.

(69) The only way in which an active bending sensor having a single cell can be used appropriately, is if the test object is designed and fixed to the location where it is used in such manner that ONLY the desired forces act effectively in it. This therefore means that no interfering mechanical forces such as torques are present.

(70) FIGS. 13a and 13b show the following: the use of only one sensor element is only to be recommended if, apart from the relevant bending forces, no other mechanical forces are applied to the test object. Otherwise, the output signal of the active bending sensor element will be a combination or mixture of the relevant and the interfering mechanical forces.

(71) Test Object Material

(72) To begin with it was assumed that the quality and performance (regarding magnetic properties) of the test object material should be similar to those necessary when bending sensors are fitted, which are based on the magnetostriction principle. These ferromagnetic materials are slightly more expensive than “normal” steels, since they have to contain nickel, chromium or similar elements, either alone or in combination.

(73) Test results (during the design and construction of an active bending sensor) have shown that a much wider selection of metallic materials than expected can be used. So long as a permanent magnet can stick to a test object, the active bending sensor too will work. To achieve the best possible measurement signal quality it is recommended to harden the test object material, at least in the sensor area. The “sensor area” is the location at which the active bending sensor will be arranged. If this is not done, the result is a relatively large measurement hysteresis.

(74) Residual Magnetic Fields in the Test Object

(75) Bending Sensor Operated with Direct Voltage (Static Field):

(76) When test object materials are used which have ferromagnetic properties and can be permanently magnetized, such a material should NOT be used with an active bending sensor operated with direct voltage. The reason for this is that such a material, at the position where the active bending sensor is located, will slowly but surely become a bar magnet (which means that the place where the active bending sensor is located will itself become a magnet after a time. Here, “after a time” means after a couple of seconds or after a couple of minutes).

(77) When that happens, the signal offset of the bending sensor output signal drifts in one direction and is therefore not stable. Conversely, it is thus only logical that a bending sensor operated with direct voltage is VERY sensitive to magnetic fields stored under the surface of the test object. Before use, the material of the test object must accordingly first be demagnetized.

(78) Bending Sensor Operated Dynamically (with Alternating Voltage):

(79) When the active bending sensor is operated in an alternating voltage mode (the field-generating coil is energized by a symmetrical alternating current of fixed frequency) AND when standard inductors with a ferromagnetic core are used, the design of the active bending sensor is in most cases INSENSITIVE to magnetic fields stored in the test object.

(80) “In most cases” means that cases are possible in which the bending sensor operated with alternating voltage is sensitive to magnetic fields stored under the surface of the test object. For example, if it is assumed that in the test object ONE magnetic point (in the sensor area) is stored, and if it is further assumed that TWO sensor coils are arranged symmetrically around the shaft, then the signal produced by the magnetic point (at a rotation speed of 300 revolutions per second (equivalent to 18,000 min.sup.−1)) will distort the internal signal decoding function of the sensor system.

(81) Sensor Electronic System

(82) Arrangement of the Sensor Coil (MFS)

(83) The orientation of the sensor coil (in relation to the magnetic field lines produced by the generating coil and the flux concentrator) determines WHICH mechanical force will be detected and measured, and HOW LARGE the amplitude of the measurement signal will be (signal quality).

(84) Field of Application

(85) With conventional bending sensor techniques it was necessary for the sensor elements to be attached firmly to the surface of the test object, in order to ensure that the relevant mechanical forces in fact acted through it so that they could be measured. The necessary cable connections (to and from the sensor element), the environmental constraints (humidity and cyclically fluctuating temperatures limit the useful life of the sensor element) and the costs associated with such sensor techniques, restrict their use and make them unusable for mass applications.

(86) The active bending sensor overcomes all these problems and can therefore be used in many different fields: the automotive industry, avionics, production technology, consumer goods, measurement and control technology, such as: diagnosis and preventative monitoring of large structures (bridges, tall buildings, etc.), real-time measurements in automotive/truck wheel suspensions for active wheel suspension or active stability control, avionics: wing loads in bad-weather situations; diagnoses in the airframe structure, DIY and professional tools: design of torque wrenches (by bending forces); and tool overloading recognition, wind power: turbine structure and propeller structure during hurricane blasts, industrial pressing machines, such as paper mills, steel production and tool equipment (detection of force limits to avoid damage to tools and materials).

(87) Functional Principles

(88) A generating coil is energized either by a direct voltage or a specific alternating voltage signal, and then produces a magnetic flux under the surface of the test object. The mechanical forces passing through the test object influence the direction of the magnetic field lines in their course from one pole of the flux concentrator to the other. The change in the direction followed by the magnetic field lines can be detected by a magnetic field sensor device arranged at the surface of the test object. The signal changes picked up by the magnetic field sensor device are proportional to the relevant mechanical forces applied to the test object.

(89) When an electric direct voltage is used to energize the field-generating coil there is a risk that a small section of the test object (depending on its material) will become permanently magnetized. This then results in a signal offset which can look like a real signal caused by mechanical forces. That problem can be overcome by using an electric alternating-voltage energizing signal to operate the field generator.

(90) However, only specific frequencies are suitable for detecting and measuring mechanical forces in the test object.

(91) Physical Dimensions of the Sensor

(92) FIGS. 14a, 14b, 14c show the following, in a side view 14a and two front views 14b and 14c: the angle.sub.MPS determines WHICH mechanical forces will be measured and what the quality of the measurement signal will be. The angle also determines potential “cross-induction” in the measurement signal, which can be caused by the various mechanical forces that may be applied to the test object.

(93) Research and Development Project:

(94) Active Sensor for Mechanical (Bending) Forces

(95) One of the main differences between a passive and an active sensor for mechanical forces, is that no “permanent” magnetization of the test object is necessary in order to obtain a functioning sensor. An active sensor for mechanical (bending) forces can start operating as soon as the sensor hardware has been suitably arranged in the close vicinity of the test object.

(96) The following task list description concentrates on one or two of the “most probable” configurations of an active sensor for mechanical (bending) forces, which achieve the desired sensor performance. The two physical hardware implementations for the sensor which have so far given the best results, are here called the glider and the monkey designs. Early results indicate that “monkey” gives slightly better results than “glider”, but “glider” is somewhat simpler to produce.

Active Sensor for Mechanical (Bending) Forces

Definitions

(97) The active sensor system comprises a number of modules: sensor hardware (flux concentrator, generating coil, feedback coil, MFS coil) electronic unit 6-conductor connecting cable between the sensor hardware and the electronic circuit electric current supply 2-conductor cable between the electronic circuit and the current supply

(98) This is shown schematically in FIG. 15.

(99) The sensor hardware is positioned laterally close to the test object (such as a driveshaft).

(100) This is shown schematically in FIGS. 16a and 16b, wherein FIG. 16a is a side view and FIG. 16b is a front view.

(101) To begin with, 40 different sensor designs were defined and almost half of them were tested. Design No. 27 produced the first usable test results. The drawing above shows Design No. 27 with substantial improvements.

(102) Target Characteristics for Satisfying Current Market Requirements

(103) Since this is a quite new sensor technique, it is difficult to define what the target characteristics should be. In principle the target characteristics are defined by the application in which the sensor is used. However, starting from a knowledge of the market acquired over the last 10 years an assumption can be made about what the “minimum” requirements are with which the active bending sensor can be expected to be successful on the market. Furthermore, it is also possible to define what an “average” specification would be like, which is here called “Standard”, and what an “Outstanding” performance of the active bending sensor would turn out to be.

(104) TABLE-US-00001 Minimum Standard Outstanding Specification Explanation typical typical typical Unit Smallest usable 20 12 10 mm shaft diameter Largest usable shaft 50 100 unlimited mm diameter Signal resolution digital equivalent 8 10 12 Bit Reproducibility percent of ±1 ±0.5 ±0.1 % max maximum Signal band width analog Hz 100 1,000 10,000 Hz Signal hysteresis when using ferro- ±2 ±0.5 ±0.2 % max magnetic materials Output signal range Maximum negative 1.5 2 4 V to maximum positive torque Signal-to-noise ratio 10 5 <2.5 mV Air gap variation Variation of the none 1.5 4 mm distance between sensor and shaft Sensor hardware radial distance 25 20 <15 mm height required for a shaft 25 mm thick Current consumption <250 <125 <75 mA Operating sensor hardware 0 to +70 −20 to +85 −40 to +150 ° C. temperature range only

(105) Dimensioning of the Active Bending Sensor

(106) To support the technical “communication” when reporting and documenting the dimensions of an active bending sensor hardware unit, the following dimension parameters were established:

(107) The respective parameters of the table below are additionally entered in FIGS. 17a, 17b, 17c, wherein FIG. 17a is a side view and FIGS. 17b and 17c show front views.

(108) The characteristic values shown below are only examples for a specific active sensor model (out of the 4 or 5 made until now). These specifications still have to be optimized and their effects in relation to sensor performance still better understood.

(109) TABLE-US-00002 Specification Symbol Explanations Min Typical Max. Unit Flux concentrator FC L 22 mm length Flux concentrator FC H 20 mm height Flux concentrator FC T 4 mm thickness Flux concentrator FC A 2.5 mm annular width Flux concentrator angle T −1 +1 degrees inclination Flux concentrator pole angle FC 60 degrees angle Angle between MFS angle MFS 88 degrees axis and field generator axis Flux concentrator steel disks material Number of metallic 1 3 elements used in the flux concentrator Distance between the distance 0.1 1.1 mm poles of the flux concentrator and the test object Distance between the MFS H 2 mm middle of the MFS coil and the test object Test object diameter TO D 15 mm Number of turns in the 100 turns generating coil Coil wire thickness 0.28 mm Axial coil length on the 10 mm flux concentrator Location relative to flux middle concentrator Specified MFS coil 400 turns turns MFS coil wire 80 μm thickness Coil body length 6 mm MFS coil body 2 mm diameter MFS coil resistance direct current 10 Ohm MFS coil manufacturer KUK

(110) Diameter of the Test Object (Example: Driveshaft)

(111) The diameter of the test object (or driveshaft) defines (besides a couple of other parameters) the signal amplification related to the bending forces. The larger the diameter of the shaft, the smaller is the signal amplification (in relation to a constant applied bending force).

(112) Note: The signal amplification of the active bending sensor is determined by a number of specific characteristics. When seeking to test the behavior of the sensor when the diameter (or cross-section area) is changed, all other sensor parameters must be kept constant, such as: identical shaft material identical hardening and annealing processes distance/gap between the test object and the sensor hardware magnetic flux density produced by the sensor hardware inductivity and driver circuit sensor hardware dimensions surface size of the two magnetic poles Adapted: the radius machined in the poles for adaptation to the shaft diameter A11

(113) FIGS. 18a, 18b, 18c show the following, in side views 18a, 18b and 18c: one and the same sensor hardware configuration is used for carrying out this test. However, the two magnetic pole surfaces that face toward the test object have to be adapted individually for each shaft diameter. It is decisive that the “gap” (distance) between the magnet poles is kept constant, in order to leave the same “room” for the MFS coil.

(114) Most probably, the signal amplification of the bending sensor is also defined by the arc characteristic of the sensor hardware. Here, arc characteristic means: “The angle over which the sensor hardware covers the test object” (see FIGS. 19a, 19b, 19c showing the side views 19a, 19b and 19c).

(115) The angle of the sensor arc A12 is different in all three of the examples illustrated above. There are two conflicting assumptions, both of them reasonable and which to a certain extent can compensate one another: The larger the arc angle, the greater is the signal amplification With a larger arc angle a larger area of the sensor surface is covered and it is easier to detect the sub-torques that distort the magnetic signal. The closer the magnetic poles come to a position on opposite sides of the shaft, the smaller is the sensor signal. In this case (when the poles are arranged on opposite sides of the shaft) the magnetic field passes almost 100% directly through the shaft material and has no effects at the surface of the shaft (on which the sensor coil is then arranged).

(116) In FIGS. 20a, 20b the shaft diameter changes and the angle A12 of the arc (sensor hardware) has been kept constant. This means that the structure of the sensor hardware essentially changes for each shaft diameter.

(117) Distance Between Shaft and Sensor

(118) There are several design possibilities, which have been tested, in order to compensate the signal amplification change automatically when the distance between the sensor and the shaft surface changes. The simplest design option is to use a feedback coil.

(119) Structure of the Feedback Coil:

(120) FIG. 21 show the following: the feedback coil A5 provides accurate information about the efficiency of the sensor or when the distance between the sensor hardware and the shaft surface changes.

(121) Flux Concentrator Material

(122) Until now, in all the tests carried out on active bending sensors “standard” disks and clamping rings have been used as the flux concentrator. Here, the term “standard” means that a large selection of disks available via professional supply channels (Hoffman Tools) and consumer markets (Obi in Germany) have been purchased and used in the structure of the sensor.

(123) The only criterion that has been applied for the decision of “which disk or clamping ring material can be used”, was that relative to a permanent magnet held close to it, the material shows a strong reaction. Until now no tests have yet been planned or carried out to determine what sensor performance differences can be achieved when a more high-grade material such as transformer steel is used.

(124) The reasons why no specific optimization of the flux concentrator material has been pursued, are as follows: The sensor performance is strongly influenced by other factors, which were the first to attract attention. The disks and clamping rings are perfectly shaped, which has simplified the original sensor design and saved time. The disks are perfectly symmetrical and are available in almost any desired sizes and thicknesses, Very low cost and ready availability.

(125) At least five different disk and clamping ring types have been used until now, which differ in the type of the material (for example hardened spring steel, unhardened disks), and coating (none, chromium, zinc, etc.). They all showed good performance. To determine which material achieves the best results and “wherein the performance differences consist”, it is necessary to purchase or to produce oneself “identically” sized and “identically” shaped flux concentrators, so that the test results can be compared with one another.

(126) Summary:

(127) Clearly, the choice of the flux concentrator material will influence the performance of the sensor. Since an active bending sensor can be used in a direct voltage mode or an alternating voltage mode, there are also different material characteristic requirements for each of these two operating modes. If the material chosen has a high remanence, it is NOT suitable for direct voltage operation since the flux concentrator, after it has been permanently magnetized, will show a different reaction from before that. It can be assumed that transformer steel will be a good choice of material. It too is widely available, but is expensive.

(128) Test Object Material

(129) At first it was assumed that the test object material should have similar quality and similar behavior (as regards its magnetic properties) to those needed when magnetostrictive bending sensors are constructed. These ferromagnetic materials are slightly more expensive than “normal” steels, since they have to contain nickel, chromium or similar elements, alone or in combination.

(130) Surprisingly, the results showed that a much larger selection of metallic materials can be used, than originally assumed. So long as a permanent magnet sticks to a test object, the active bending sensor too will function.

(131) Residual Magnetic Fields in the Test Object

(132) Active Sensor Operated with Direct Voltage (Static Field):

(133) When test object materials are used which have ferromagnetic properties and can be permanently magnetized, such materials should NOT be used with an active bending sensor operated with direct voltage. The reason for this is that at the point where the active bending sensor is positioned, such a material will slowly but surely become a bar magnet (which means that the place where the active bending sensor is positioned will itself become a magnet after a time. Here, “after a time” means after a couple of seconds or after a couple of minutes).

(134) When that happens, the signal offset of the bending sensor drifts in one or other direction and is then not stable. Conversely, it is therefore only logical that an active bending sensor operated with direct voltage is VERY sensitive to magnetic fields stored under the surface of the test object. Accordingly, before use the material of the test object must first be demagnetized.

(135) Active Bending Sensor Operated Dynamically (with Alternating Voltage):

(136) When the active bending sensor is operated in an alternating voltage mode (the field-generating coil is energized by a symmetrical alternating current with a defined frequency) AND standard inductors with a ferromagnetic core are used then the design of the active bending sensor is in most cases INSENSITIVE to magnetic fields stored in the test object.

(137) “In most cases” means that cases are possible, in which the active bending sensor operated with alternating voltage is sensitive to magnetic fields stored under the surface of the test object. For example, if it is assumed that ONE magnetic point is stored in the test object (in the sensor area), and if it is further assumed that TWO sensor coils are arranged symmetrically around the shaft, then the signal produced by the magnetic point (at a rotation speed of 300 revolutions per second (equivalent to 18,000 min.sup.−1)) will disturb the internal signal coding function of the sensor system.

(138) Inclination of the Flux Concentrator

(139) Most probably, an inclination of the flux concentrator will reduce the signal amplification (see FIGS. 22a, 22b, 22c, with the side view 22a and the front views 22b and 22c, wherein the magnetic flux concentrator A2 is inclined in FIG. 22c).

(140) Material Thickness of the Flux Concentrator

(141) The thickness of the flux concentrator device defines the precision with which a specific mechanical force can be selectively identified and measured. It is important that the magnetic field lines produced pass through the surface of the test object, in order to ensure a sufficient signal amplitude produced by the magnetic field sensor device. If the flux concentrator is made too thin, then the field generated by the field-generating coil produces undesired magnetic stray fields.

(142) The magnetic field concentrator A2 and the alternative designs thereof, A2′, A2″ and A2′″, are shown in FIG. 23.

(143) It still has to be tested and evaluated how the sensor performance changes when the flux concentrator thickness is reduced, or what effect the shape of the front parts (the two poles) has. To make the pole area very slender, the pole ends can be “pointed”. The potential advantage of this is that such a structure is less sensitive to an inclination of the flux concentrator.

(144) Flux Concentrator Profile

(145) A mechanical structure with a “low profile” is preferred for most applications. However, great care must be taken that no sharp “corners” remain on the flux concentrator, since the magnetic field will then emerge there and produce undesired stray fields.

(146) It is also important to ensure that the surface of the test object does not come too close to the upper end of the flux concentrator, because otherwise that part of the flux concentrator interferes with the measurement signal (“steals” the magnetic signal that should be detected and captured by the MFS device).

(147) FIGS. 24a, 24b show a side view of the following: it is important to keep as small as possible the radial space needed by the active torque sensor, in order to accommodate that sensor in small fitting spaces. However, by reducing the radial dimensions the generating coil comes closer to the sensor coil and also closer to the test surface, which can lead to a deterioration of the sensor performance that can otherwise be achieved. The figures show a magnetic flux concentrator A2 and another alternative configuration A2″″.

INDEXES

(148) 1 Chassis component 1a Measurement fixture 1b Metallic, magnetic portion 1c Connecting strut 1d Ball bearing 1e Ball bearing 1f Weld seam 2 Housing 2a Upper housing half 2b Lower housing half 2c Cast mass 2d Projection 3 Field-generation means 3a First field-generating means 3aa Field concentrator 3b Second field-generating means 3ba Field concentrator 4 Cable 5 Detection means 5a First detection means 5b Second detection means 6a Aperture 6b Fastener 6c Fixing structure 7 Electronic means x Distance M Central plane NF Neutral fiber A1 Test object A2 Magnetic flux concentrator A3 Magnetic field generating coil A4 Magnetic sensor element A5 Signal feedback coil A6 Current supply A7 Signal generator A8 Filter & power driver A9 Filter & gain A10 Variable gain amplifier A11 Shaft diameter A12 Angle of the sensor arc