Optical sensor, in particular for a cylinder, and application

Abstract

A sensor (S) is provided for determining the stroke of the piston rod (6) of a fluid cylinder, particularly a hydraulic or pneumatic cylinder. The sensor includes a lighting unit for illuminating a code applied on the surface of the piston rod and differing from said surface by color, a first camera unit with a first lens system for recording a first image of the illuminated code in a first scanning window, an evaluation unit for evaluating output signals of the first camera unit, and an interface for issuing the evaluated output signals as information regarding the position of the piston rod. Additionally, a second redundant camera unit is provided with a second lens system, which serves for recording a second image of the illuminated code in a second scanning window. According to the invention the second camera unit is arranged such that the second scanning window is spaced apart in the direction of the extension of the piston rod by a predetermined value from the first scanning window of the first camera unit. The output signals of the second camera unit are evaluated in an evaluation unit as information about the respective position by forming a difference, with in case of said difference being consistent with a predetermined value the output signal being considered information about the stroke of the piston rod, and in case of inconsistency of the difference with the predetermined value an error message being issued.

Claims

1. A sensor (S) for determining a stroke of a piston rod (6) of a fluid cylinder (8), the sensor (S) comprising: a lighting unit for illuminating a code applied on a surface of the piston rod (6) and differing therefrom in color, a first camera unit (1a, 3a) with a first lens system (1a) for recording a first image of the illuminated code in a first scanning window (12), an evaluation unit for evaluating output signals of the first camera unit (1a, 3a), an interface for emitting an evaluated output signal as information regarding a position of the piston rod (6), and a second camera unit (1b, 3b) with a second lens system (1b) for recording a second image of the illuminated code in a second scanning window (13), wherein the second camera unit (1b, 3b) being arranged such that the second scanning image (13) is spaced apart in a direction of extension of the piston rod (6) by a predetermined value (L) from the first scanning window (12) of the first camera unit (1a, 3a), and output signals of the second camera unit (1, 3b) being evaluated in the evaluation unit as information regarding a respective position when forming a difference, with in case the difference is consistent with the predetermined value (L) the output signal is provided as information regarding the stroke of the piston rod (6), and in case the difference is not consistent with the predetermined value (L) an error message is issued.

2. The sensor according to claim 1, wherein the first lens system and the second lens system are arranged in a common optic housing (2).

3. The sensor according to claim 1, wherein the first camera unit (1a, 3a) and the second camera unit (1b, 3b) each comprise a photosensitive sensor element (3a, 3b), with the two sensor elements (3a, 3b) being arranged on a common circuit board (4).

4. The sensor according to claim 1, wherein the second camera unit (1b, 3b) is arranged such that the first and the second scanning window (12, 13) overlap each other.

5. The sensor according to claim 1, wherein the code is at least one of embodied as a continuous, unambiguous binary barcode, or has a code structure absolutely illustrating the actual stroke of the piston rod (6).

6. The sensor according to claim 1, wherein a change of the position of the piston rod (6) by maximally a width of one bar of the code leads to an unambiguous code word and intermediate positions, which are smaller than the width of the bars of the code is determined by way of interpolation.

7. The sensor according to claim 1, further comprising at least a third camera unit arranged radially in reference to the direction of extension of the piston rod (6).

8. The sensor according to at least claim 3, wherein the circuit board (4) is arranged essentially parallel in reference to a longitudinal axis of the piston rod (6), or arranged inclined in reference to the longitudinal axis of the piston rod (6) by approximately 20 degrees.

9. The sensor according to claim 1, wherein the first camera unit (1a, 3a) and the second camera unit (1b, 3b) are arranged in a common sensor housing (5).

10. A cylinder/piston aggregate comprising: a fluid cylinder (8), a piston (9) longitudinally mobile in the fluid cylinder, a piston rod (6) supported thereby, with a code being applied on a surface thereof differing therefrom in color, and a sensor (S) according to claim 1.

11. A method for determining a stroke or length of a piston rod (6) of a fluid cylinder of a work machine, construction machine, or agricultural machine, comprising: providing a sensor according to claim 1; and evaluating output signals of the first and second camera units to determine the stroke or benefit of the piston rod.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) As already explained above, there are various options to advantageously implement the teaching of the present invention and to further develop it. For this purpose, additional embodiments, features, and advantages of the present invention are explained in greater detail based on the exemplary embodiments illustrated in FIGS. 1A to 3B.

(2) Shown are:

(3) FIG. 1A in a schematic illustration of the concept, a first exemplary embodiment for the sensor according to the invention, which operates based on the principle of absolute length measurement of the present invention;

(4) FIG. 1B in a schematic illustration of the concept, an enlarged illustration of a second exemplary embodiment for the sensor according to the present invention, which operates according to the principle of absolute length measurement of the present invention;

(5) FIG. 1C a detail of FIG. 1A, which shows the sensor with the two redundant camera units in an enlarged illustration;

(6) FIG. 2 a schematic illustration of the concept, visualizing the safety principle implemented in the present invention;

(7) FIG. 3A in a schematic illustration of the concept, an exemplary embodiment for arranging the sensor of FIG. 1A or FIG. 1B in reference to a piston rod provided with a continuous and unambiguous binary barcode;

(8) FIG. 3B in a schematic illustration of the concept, an exemplary embodiment for the arrangement of the sensor of FIG. 1A or FIG. 1B and FIG. 3A in the undercarriage of a mobile crane, and

(9) FIG. 4 a third exemplary embodiment of a second circuit board, inclined in reference to the camera circuit board, with a LED as the light soured.

(10) Identical or similar embodiments, elements, and features are provided with identical reference characters in FIGS. 1A to 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) A preferred exemplary embodiment of the present invention is illustrated based on FIG. 1A.

(12) The sensor S comprises a lighting unit and two camera units, in addition to an integrated or allocated evaluation unit, particularly an evaluation electronic, which may be realized for example via a DSP or CPU. Each of the two camera units, essentially arranged linearly in reference to the longitudinal extension of a piston rod 6, comprises a lens system 1 and a photosensitive sensor element 3 arranged on a circuit board 4, with the lens system 1 and the sensor element 3 being provided in an optic housing 2. Optic housings 2 and circuit boards 4 are in turn arranged in a housing 5. The sensor elements 3 are particularly embodied as CCD-image sensors (CCD: charge-coupled device), which comprise a matrix of light-sensitive elements, such as photodiodes, and which can record a two-dimensional image.

(13) The two cameras arranged axially at a distance from each other by a distance L detect the absolute barcode on the piston rod 6 (located underneath thereof in FIG. 1A) and this way they determine the presently given position of the piston rod 6 independently from each other.

(14) In the exemplary illustration according to FIG. 1A the circuit board 4 is arranged at least essentially parallel in reference to the longitudinal extension of the piston rod 6.

(15) According to an alternative embodiment of the present invention, illustrated in FIG. 1B, the circuit board 4 can be arranged inside the housing 5 in an inclined fashion in reference to the longitudinal extension of the piston rod 6 (not shown in FIG. 1B for reasons of clarity of the illustration), for example inclined by approximately twenty degrees (FIG. 1B showing only one camera unit for reasons of clarity of the illustration).

(16) Such a diagonal design, i.e. angled position of the circuit board 4 in reference to the piston rod 6, allows measuring the apex of the piston rod 6, this means the stroke of the piston rod 6 is determined independently from its diameter.

(17) FIG. 1C shows the sensor illustrated in FIG. 1A once more in an enlarged fashion for better understanding. Here, the sensor element of the first camera unit abutting the cylinder head of the fluid cylinder 8 is marked with the reference character 3a and the sensor element of the second, redundant camera unit is marked with the reference character 3b. Accordingly, the right lens system at the right in FIG. 1C is marked 1a and the left lens system is marked 1b. The dot-dash lines show schematically the radiation path of the optical illustration generated by the respective lens system 1a, 1b. The lens system 1a forms the detection range 12 on the image sensor 3a, which is equivalent therefore to the scanning window of the first camera unit. Accordingly, the second lens system 1b displays the detection range 13 on the image sensor 3b. This is therefore equivalent to the scanning window of the second camera unit.

(18) The distance L is equivalent to the distance of the two scanning windows 12, 13 and can be measured in the center of the scanning window or also its respectively right or left edge. Due to the fact that the two sensor elements 3a, 3b are also located in the optic axis of the lens systems 1a, 1b and are thus also offset on the circuit board 4 by the distance L (measured e.g., in the respective center of the two otherwise identical sensor elements 3a, 3b). The optic housing 2, in which the two lens systems 1a, 1b are arranged in appropriate seats, is fastened above the two sensor elements 3a, 3b on the circuit board 4. The gasket 10a, located about the piston rod 6, and preferably allocated to the sensor housing 5, prevents the penetration of contaminants into the sensor housing 5.

(19) An essential advantage of the redundant sensor S, here comprising various integrated plausibility checks, according to FIG. 1 or according to FIG. 1B therefore also results from a safety analysis according to FIG. 2 (here, indicating recognized position camera picture flawless code gap defective code if recognizable as position distance between sensors failure detected).

(20) If for example values measured successively deviate from each other in a non-plausible fashion, an error message is generated and issued. For safety-critical applications, for example for braking or steering systems, this way of checking is frequently insufficient, though.

(21) For this purpose, the redundant system according to the invention is available in which the two sensor units are integrated in the same housing 5. The housing 5 is only slightly greater in the sensor S according to the invention showing two or more sensors than in the one-channel sensor. For this purpose the overall system is considerably more space-saving and here no increased expense is required for wiring.

(22) Both sensors are arranged side-by-side in the longitudinal direction. Based on this arrangement the two sensors scan the same code bars, however at different locations and at a fixed predetermined distance L. If the two measurements fail to reflect this distance L, this fact is detected as an error.

(23) Scanning the barcode at two axially offset points increases the safety of the sensor S.

(24) If for example a bar is too wide or too narrow due to a faulty marking on the piston rod 6, it could happen that the respective point is misinterpreted and this way a false measurement is issued.

(25) However, if the code is evaluated at two different points, almost all faulty codes can be detected. This way the occurrence of undetectable dangerous errors can be excluded almost entirely.

(26) Furthermore for some errors it is possible to correct such errors, which increases the availability.

(27) Here, the distance L of the two sensors is selected fixed in reference to each other. This way, the requirement must be fulfilled at all times that the two detected positions always deviate from each other by said distance L. If this condition is not met, at least one measurement must have been detected erroneously. This is possible for example when the code is false, soiled, or damaged.

(28) This increases the safety of the issued measurement, because here potential scanning errors are reliably detected. In order for the sensor S to issue a false value, both partial sensors had to detect the false value each simultaneously, and both values detected falsely had to show precisely the distance L from each other. This is very improbable in a suitably designed barcode.

(29) The barcode, which the piston rod 6 is provided with, is evaluated in the longitudinal direction of the piston rod 6 in case of the redundant system according to the present invention simultaneously at two different positions using the evaluation electronic, here for example at the position X and at the position Y=X+L.

(30) If here a position is detected incorrectly, for example by a code applied in a flawed or damaged fashion, (cf. defective code in the lower half of FIG. 2), it is immediately detected in a plausibility check.

(31) Due to its design, the reliability of its components, and its safety measures the sensor is suited to meet the requirements according to the European standard (EN) ISO 13849-1.

(32) From the schematic illustration in FIG. 3A it is discernible, for example, that the sensor S can be considered an external sensor, which however is largely integrated in the construction of the fluid cylinder, particularly the hydraulic or pneumatic cylinder, and with its installation potentially being adjusted to the respective application.

(33) Based on its compact dimensions the sensor is particularly suited for the mobile use in machines for agriculture and construction. For example, the sensor according to the present invention can be used in the undercarriage of mobile cranes (cf. FIG. 3B).

(34) The sensor is integrated in the telescopic cylinders of support arms in order to measure the width of said support arm, allowing the determination of the tipping load of the crane.

(35) Based on the embodiment shown in FIG. 1B, FIG. 4 illustrates another exemplary embodiment in which a light emitting diode 16 is arranged, serving as a lighting unit on a second circuit board 15. The second circuit board is inclined in the opposite direction compared to the circuit board 4, namely preferably by the same angle as the circuit board 4, so that the radiation path of the incident angle between the light emitting diode 16 and the surface of the piston rod 6 is equivalent to the emergent angle between the piston rod 6 and the camera unit.

(36) Similar to FIG. 1B, FIG. 4 also shows only one camera unit. The second one is arranged offset in the drawing plane and covered by the first one.