Position controlled electrodynamic linear motor

Abstract

A linear drive for a miniaturized optical system, as used for example in an endoscope, includes a stator and an armature. The stator has a coil with two stator pole shoes arranged in axial direction, and two magnetic field sensors arranged at the outer side of the stator pole shoes. The armature has permanent magnets which are polarized in opposite directions, and a center armature pole shoe between the two permanent magnets, and an armature pole shoe at each side of the permanent magnet, opposite to the center armature pole shoe in axial direction. The magnetic field of the outer armature pole shoe goes completely or only in part, dependent from the armature position, through the magnetic field sensor and thus generates a position-dependent signal. This signal can be used for measuring and/or controlling the position of the armature.

Claims

1. A linear drive comprising: a ring-shaped stator having a center axis, the stator further comprising: a magnetic coil, a first ring-shaped stator pole shoe and a second ring-shaped stator pole shoe, each pole shoe being at one side of the coil, a magnetic member enclosing the coil in radial direction a first field sensor in axial direction next to the coil on the side of the first stator pole shoe, a second field sensor in axial direction next to the coil on the side of the second stator pole shoe, a hollow armature being moveable in axial direction in the stator, the armature further comprising: a first ring-shaped permanent magnet and a second ring-shaped permanent magnet, the permanent magnets being polarized axially in opposite directions, a ring-shaped center armature pole shoe between the two permanent magnets, a ring-shaped first outer armature pole shoe at a side of the first permanent magnet, said side being opposite to the middle armature pole shoe in axial direction, and a ring-shaped second outer armature pole shoe at a side of the second permanent magnet, said side being opposite to the middle armature pole shoe in axial direction, wherein at least a part of the magnetic flux of the first outer armature pole shoe and the second outer armature pole shoe goes through at least one of the field sensors.

2. The linear drive according to claim 1, wherein at least one of the field sensors is arranged in an opening of a respective stator pole shoe, or is integrated in the stator pole shoe or is enclosed by the magnetic member in radial direction.

3. The linear drive according to claim 1, wherein an evaluation circuit is provided, the evaluation circuit generates a signal for indicating the position of the armature by means of the sum of signals of the both field sensors and/or it compares a setpoint value for a position of the armature with a measured value of at least one signal of at least one field sensor, and generates a control signal for keeping the position of the armature constant.

4. The linear drive according to claim 1, wherein at least one stator pole shoe and/or at least one armature pole shoe and/or the magnetic member comprises at least one ferromagnetic material.

5. The linear drive according to claim 1, wherein the armature has a bore for holding an optical element.

6. The linear drive according to claim 1, wherein a sliding sleeve with a non-ferromagnetic material having a low friction coefficient is arranged at a surface between stator and armature.

7. The linear drive comprising: a ring-shaped stator having a center axis, the stator further comprising: a magnetic coil, having a ring-shaped stator pole shoe at one side in the direction of the center axis, a magnetic member enclosing the coil in radial direction, a field sensor integrated into the stator pole shoe, a hollow armature being moveable in axial direction in the stator, the armature further comprising: a ring-shaped permanent magnet, a ring-shaped first outer armature pole shoe and a ring-shaped second outer armature pole shoe, the pole shoes being at axially opposite sides of the permanent magnet, wherein at least a part of the magnetic flux of the first outer armature pole shoe goes through the field sensor.

8. The linear drive according to claim 7, further comprising a second field sensor, the second field sensor being integrated in the stator pole shoe and displaced in axial direction against the first field sensor.

9. The linear drive according to claim 7, wherein the field sensor is arranged in an opening of a respective stator pole shoe, or is integrated in the stator pole shoe or is enclosed by the magnetic member in radial direction.

10. The linear drive according to claim 7, wherein an evaluation circuit is provided, the evaluation circuit generates a signal for indicating the position of the armature by means of the sum of signals of the both field sensors and/or it compares a setpoint value for a position of the armature with a measured value of at least one signal of at least one field sensor, and generates a control signal for keeping the position of the armature constant.

11. The linear drive according to claim 7, wherein at least one stator pole shoe and/or at least one armature pole shoe and/or the magnetic member comprises at least one ferromagnetic material.

12. The linear drive according to claim 7, wherein the armature has a bore for holding an optical element.

13. The linear drive according to claim 7, wherein a sliding sleeve with a non-ferromagnetic material having a low friction coefficient is arranged at a surface between stator and armature.

14. The linear drive comprising: a ring-shaped stator having a center axis, the stator further comprising: a first magnetic coil and a second magnetic coil, a ring-shaped stator pole shoe, the stator pole shoe being arranged between the magnetic coils, a magnetic member enclosing the coils in radial direction a first field sensor and a second field sensor, both field sensors being integrated in the stator pole shoe and are displaced in axial direction against each other, a hollow armature being moveable in axial direction in the stator, the armature further comprising: a first ring-shaped permanent magnet and a second ring-shaped permanent magnet, the permanent magnets polarized axially in opposite directions, a ring-shaped center armature pole shoe between the two permanent magnets, a ring-shaped first outer armature pole shoe at a side of the first permanent magnet, said side being opposite to the middle armature pole shoe in axial direction, and a ring-shaped second outer armature pole shoe at a side of the second permanent magnet, said side being opposite to the middle armature pole shoe in axial direction, wherein at least a part of the magnetic flux of the center armature pole shoe goes through at least one of the field sensors.

15. The linear drive according to claim 14, wherein at least one of the field sensors is arranged in an opening of a respective stator pole shoe, or is integrated in the stator pole shoe or is enclosed by the magnetic member in radial direction.

16. The linear drive according to claim 14, wherein an evaluation circuit is provided, the evaluation circuit generates a signal for indicating the position of the armature by means of the sum of signals of the both field sensors and/or it compares a setpoint value for a position of the armature with a measured value of at least one signal of at least one field sensor, and generates a control signal for keeping the position of the armature constant.

17. The linear drive according to claim 14, wherein at least one stator pole shoe and/or at least one armature pole shoe and/or the magnetic member comprises at least one ferromagnetic material.

18. The linear drive according to claim 14, wherein the armature has a bore for holding an optical element.

19. The linear drive according to claim 14, wherein a sliding sleeve with a non-ferromagnetic material having a low friction coefficient is arranged at a surface between stator and armature.

20. A camera with a linear drive according to claim 1, wherein the linear drive is provided for the control of at least one optical component.

21. An endoscope with a linear drive according to claim 1, wherein the linear drive is provided for the control of at least one optical component.

22. A medical instrument having a linear drive according to claim 1, wherein the linear drive is provided for adjusting the aperture angle of a jaw section.

23. The camera with a linear drive according to claim 7, wherein the linear drive is provided for the control of at least one optical component.

24. Endoscope with a linear drive according to claim 7, wherein the linear drive is provided for the control of at least one optical component.

25. The medical instrument having a linear drive according to claim 7, wherein the linear drive is provided for adjusting the aperture angle of a jaw section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings.

(2) FIG. 1 schematically shows a linear drive in a longitudinal section.

(3) FIG. 2 shows a linear drive in a cross-section.

(4) FIG. 3 shows the magnetic flux in a first armature position.

(5) FIG. 4 shows the magnetic flux in a second armature position.

(6) FIG. 5 shows the magnetic flux in a third armature position.

(7) FIG. 6 shows a further embodiment with only one stator pole shoe.

(8) FIG. 7 shows a further embodiment with two coils.

(9) FIG. 8 shows the sensor signals of an embodiment of FIG. 1, in dependence of the position.

(10) FIG. 9 shows the difference of the sensor signals, in dependence of the position.

(11) FIG. 10 shows the sensor signals in an embodiment according to FIG. 6.

(12) FIG. 11 shows an endoscope with a prism pivotable by a linear motor.

(13) While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

(14) FIG. 1 schematically shows a linear drive in a longitudinal section. According to a preferred embodiment, the linear drive is arranged mainly rotationally symmetric around the center axis 30. It comprises a stator 10 and an armature 20.

(15) The stator 10 has a coil 14, which preferably is enclosed by a cylindrical magnetic member 11 in radial direction. The coil 14 is enclosed by a first stator pole shoe 12 and a second stator pole shoe 13 in axial direction. Preferably, also these stator pole shoes are enclosed by the magnetic member in radial direction. Furthermore, a first magnetic field sensor 15 is arranged at the side of the first stator pole shoe 12 in axial direction next to the coil, and a second magnetic field sensor 16 is arranged at the side of the second stator pole shoe 13 in axial direction next to the coil 14. Preferably, at least one magnetic field sensor is arranged in an opening of a stator pole shoe. More preferably, this opening extends in axial direction, as shown in this Figure, but it may also extend in radial direction. The opening may be continued into the magnetic member 11, in order to offer sufficient mounting space for a bigger field sensor. Preferably, the stator pole shoes and/or the magnetic member are ring-shaped.

(16) The armature has a first permanent magnet 21 and a second permanent magnet 22, which are polarized in opposite directions and preferably parallel to the center axis. A center armature pole shoe 24 is arranged between the two permanent magnets. At the sides opposite to the center armature pole shoe 24 in axial direction, a first outer armature pole shoe 23 is arranged towards the first pole shoe 21, and a second outer armature pole shoe 25 is arranged towards the second pole shoe 22. Preferably, the armature is hollow, more preferably hollow-cylindrical. Preferably, the permanent magnets and/or armature pole shoes are ring-shaped. In some embodiments, a sliding sleeve 90 may be arranged between the stator 10 and the armature 20.

(17) Preferably, the two magnetic field sensors 15, 16 are arranged in the same plane through the center axis 30, but they may also be arranged in other planes.

(18) Preferably, the drive is construed such that within the moving distance, no axially directed reluctance forces act in a currentless state. If the coil 14 is energized, a Lorentz-force is generated, which acts on the armature, independently of its position.

(19) Basically, this embodiment, as well as all other embodiments illustrated in this specification, may be realized with an ironless stator. Thereby, the stator pole shoes 12, 13 as well as the magnetic member 11 would consist of non-ferromagnetic material or would even be omitted. Due to the absent magnetic field conductive materials in the stator, the magnetic flux density in the magnetic circuit is reduced. Thereby, also the driving Lorentz-force by an electrical current flow in the coil is reduced.

(20) In FIG. 2, a view towards the center axis 30 is shown. Here, the preferred concentric arrangement of the components is illustrated in detail. In this embodiment, the first field sensor 15 is arranged in an opening, which protrudes through the magnetic member 11 into the first stator pole shoe.

(21) In FIGS. 3, 4 and 5, the magnetic field profiles in different positions of the armature 20 relative to the stator 10 are shown. In FIG. 3, the armature 20 is shown displaced to the left relative to the center position, which is shown in FIG. 4. In FIG. 5, it is displaced to the right. Basically, a first magnetic circuit 41 is generated, starting from the first permanent magnet 21. The magnetic field goes through the first outer armature pole shoe 23 via the first field sensor 15 and the first stator pole shoe 12, respectively, continuing through the magnetic member 11, via the coil 14 and further continuing to the center armature pole shoe 24 and back to the first permanent magnet 21. Accordingly, the second magnetic circuit 42 is oriented in opposite direction.

(22) The lines 41 and 42 symbolically illustrate the magnetic field curve. In fact, the magnetic field spreads, for example, over the whole front side of the permanent magnets 21, 22. Similarly, the magnetic field spreads in radial direction out of the armature pole shoes over the surface.

(23) In FIG. 3 it can be seen that a main part of the magnetic field goes through the first field sensor 15, while the negligible part goes through the first stator pole shoe 12. The magnetic field starting from the second armature pole shoe 25 mainly goes over the second stator pole shoe 13 into the magnetic member 11. Only a minimal and negligible part will run through the second field sensor 16.

(24) In FIG. 4, a part of the magnetic field goes out of the first armature pole shoe 23, via the first field sensor 15, and parallel thereto via the first stator pole shoe 12 into the magnetic member 11. Similar holds true for the magnetic field out of the second armature pole shoe 25. Here, the field divides as well between the second field sensor 16 and the second stator pole shoe 13.

(25) In FIG. 5, the main part of the magnetic field goes out of the first armature pole shoe 23 via the first stator pole shoe 12 into the magnetic member 11, while the main part of the magnetic field out of the second armature pole shoe 25 goes through the second field sensor 16.

(26) In FIG. 6, a further embodiment is shown. In this embodiment, the stator has only one stator pole shoe 12, and the armature has only one permanent magnet 21. A first field sensor 17 and optionally a second field sensor 18 are provided. Preferably, integrated field sensors 17, 18 with smaller construction size are used, which can be integrated into the first stator pole shoe 12. Preferably, these are inserted into a recess of the first stator pole shoe 12. The field sensors 17, 18 are disposed opposite to each other, in axial direction. Preferably, they can also be arranged in different planes through the rotation axis. In this embodiment, they are arranged in the same plane, on different sides of the rotation axis. Dependent from the position of the armature 20 relative to the stator 10, the magnetic flux flows, starting from the first outer armature pole shoe 23, through one of the field sensors. In the illustrated position, a major part of the magnetic flux flows through the second field sensor 18, while the first field sensor is in a space free of fields.

(27) In the arrangement shown here, the magnetic field sensor can only lie in the magnetic field of a pole shoe. Thereby, simplified magnetic field sensors can be implemented, which deliver an output signal independent of the direction of the magnetic field. Such sensors are, for example, GMR—(Giant Magneto Resistance) sensors. In the prior art, it is often necessary to use direction-sensitive magnetic field sensors, such as Hall sensors, in order to achieve an accurate position determination. Such sensors are in most cases bigger, more expensive, and require a more complex control and evaluation circuitry.

(28) The integration of the magnetic field sensors in the stator pole shoe allows a significantly improved exploitation of space, in particular in miniature motors. This embodiment is at the same time more robust, as the magnetic field sensors are supported mechanically by the stator pole shoe. As a result, a separate housing for the magnetic field sensors can be omitted.

(29) Basically, in this embodiment of a linear drive, also an arrangement with a first magnetic field sensor 15 next to a first stator pole shoe 12, as in the embodiment of FIG. 1, may be implemented. Similarly, the embodiment of FIG. 1 may be realized with a first field sensor 17 which is integrated into the first stator pole shoe 12, according to this embodiment. Preferably, then also the second field sensor 16 of the embodiment of FIG. 1 is replaced by second field sensor 18, which is integrated into the second stator pole shoe 13.

(30) In FIG. 7, a further embodiment of the invention is shown. The armature 20 corresponds to the armature of the first embodiment, as shown, for example, in FIG. 1. Here, the stator has a first coil 14 and a second coil 19. The coils may be operated single-phased (identical current strength) or double-phased (different current strength in both coils). A stator pole shoe 12 is arranged between the two coils. The coils and the stator pole shoe are enclosed by the magnetic member 11. The field sensors 17, 18 are disposed one to another, in axial direction, and are integrated into the stator pole shoe 12, or are received by the recesses of the stator pole shoe. The magnetic field of the middle armature pole shoe 24 goes as a whole or partly—depending on the position of the armature—through the first field sensor 17 or the second field sensor 18. The output signals of the field sensors 17, 18 correspond approximately to the curves 61 and 62 of FIG. 8. Also here, a signal according to FIG. 9 can be achieved by subtraction of the signals.

(31) FIG. 8 shows the signal curve of the field sensors, for example according to the illustrations in FIGS. 3, 4 and 5. The diagram shows on the horizontal axis the distance relative to the zero position “0” in millimeters, which corresponds, for example, to FIG. 4. A deflection of −2 mm corresponds to FIG. 3, and a deflection of +2 mm corresponds to FIG. 5. On the vertical axis, the amplitudes of the sensor signals are scaled and indicated from 0-150. The curve 61 shows the signal of the first field sensor 15, while the curve 62 shows the signal curve of the second field sensor 16.

(32) Curve 61 shows on the left side, a maximal amplitude at a deflection of −2 mm, which corresponds to the maximal magnetic flux density through the first magnetic field sensor 15. This is achieved by the position of the armature as shown in FIG. 3. At the same time, the second field sensor 16 is in a nearly field free space, such that the sensor signals according to curve 62 are nearly zero. In the center position according to FIG. 4, the flux density of both field sensors is approximately equal, such that also both curves 61 and 62 have the same amplitude at position “0”. At the right position at +2 mm, the sensor signals behave in a reversed manner as in the left position. Here, the maximal magnetic flux density is through the first magnetic field sensor 16, while the first field sensor 15 lies in a nearly field free space.

(33) FIG. 9 shows the sum of curves 61 and 62 of FIG. 8 in curve 63. This curve can be well approximated by linear approximation 64. A measurement signal results, which is approximately proportional to the position of the armature. This measurement signal generally can be input into a control loop, such that the position of the armature can be kept constant, in dependence of a setpoint value.

(34) FIG. 10 shows the signals of the field sensors in an arrangement according to FIG. 6. Also here, the horizontal axis shows the displacement towards the center axis, while the vertical axis indicates the amplitude of the sensor signals. Curve 65 indicates the signal amplitude of the first field sensor 17, while the second curve 65 indicates the signal amplitude of the second field sensor 18. As a result, the exact position can be determined by evaluating which sensor outputs a signal, in combination with the signal amplitude of the sensor. In this example, only two sensors are shown. Of course, any higher number of magnetic field sensors may be used, in order to increase the resolution and/or maximal path length.

(35) FIG. 11 shows an endoscope 80, in which a linear drive 84 is implemented for adjustment of the viewing angle φ. The endoscope has a distal shaft 81 as well as a proximal ocular 83. Optionally, connections 82 for light input or for input of fluids and gases may be provided. The endoscope has an axis 88, which preferably is also the optical and/or mechanical axis. At the distal end of the shaft 81, a prism 85 is arranged pivotably around the bearing 86. The prism allows a deflection of the optical beam path, such that light entering into the distal end of the endoscope under various viewing angles φ can be detected. Adjustment of the prism is conducted by means of a linear drive 84 via a push/pull-rod 87.

(36) It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide a linear drive or linear motor and an endoscope. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

LIST OF REFERENCE NUMERALS

(37) 10 stator

(38) 11 magnetic member

(39) 12 first stator pole shoe

(40) 13 second stator pole shoe

(41) 14 coil

(42) 15 first field sensor

(43) 16 second field sensor

(44) 17 first integrated field sensor

(45) 18 second integrated field sensor

(46) 19 second coil

(47) 20 armature

(48) 21 first permanent magnet

(49) 22 second permanent magnet

(50) 23 first armature pole shoe

(51) 24 second armature pole shoe

(52) 25 third armature pole shoe

(53) 30 center axis

(54) 41 first magnetic circuit

(55) 42 second magnetic circuit

(56) 51 first lens

(57) 52 second lens

(58) 61 signal curve first field sensor

(59) 62 signal curve second field sensor

(60) 63 difference of signal curves

(61) 64 linear approximation

(62) 65 signal curve first integrated field sensor

(63) 66 signal curve second integrated field sensor

(64) 80 endoscope

(65) 81 endoscope shaft

(66) 82 connection

(67) 83 ocular

(68) 84 linear drive

(69) 85 prism

(70) 86 bearing

(71) 87 push/pull-rod

(72) 88 center axis