Device for measuring changes in length

Abstract

The present invention relates to a device (10, 10') for measuring a change in length (ΔL). The device includes a first fixed element (11, 11'), a second fixed element (12, 12'), and at least one length element (15) disposed between the two fixed elements (11, 11', 12, 12'). The at least one length element (15) has a first end (15a), a second end (15b), and a length (L) along a longitudinal direction (R). A force (F) acting parallel to the longitudinal direction (R) causes a change in length (ΔL) of the at least one length element (15). A lever element (20) has a first end (20a), a second end, and a fulcrum (D) and is disposed transverse to the longitudinal direction (R). The lever element (20) has a first lever arm (21) and a second lever arm (22), the first lever arm (21) having a first length (a) between a fulcrum (D) and a first lever arm end (21a), and the second lever arm (22) having a second length (b) between the fulcrum (D) and a second lever arm end (22b), the second length (b) being greater than the first length (a). At least one length element (15) has its first end (15a) pivotally disposed on the first lever arm end (21a) of the first lever arm. The second lever arm end (22b) of the second lever arm (22) is connected to the material measuring unit (30), and its movement is detectable by a scanning element (40).

Description

[Technical Field]

[0001] The present invention relates to a device for measuring changes in length according to the generic term of claim 1. [Background technology]

[0002] In automation technology, six-axis force-torque sensors are frequently used to measure forces and moments in all directions. Such sensors can be used in a variety of fields, such as automated joining or assembly of workpieces, deburring, polishing and grinding, and tactile measurements. These sensors measure forces (Fx, Fy, Fz) and moments (Mx, My, Mz) with respect to three coordinates (x, y, z). On the one hand, such sensors must be as rigid as possible to prevent the sensor itself from being deformed by the forces and moments. On the other hand, they must be able to achieve the highest possible resolution of the measured signal, which is generally impossible with rigid sensors. In the case of known sensors, strain gauges are used to measure forces and moments, and these strain gauges can measure very small material strains. However, the application of strain gauges is quite complex. Furthermore, the strain gauges require significant signal amplification, which leads to the high cost of such six-axis force-torque sensors. Summary of the Invention [Problem to be solved by the invention]

[0003] It is therefore an object of the present invention to provide an apparatus for measuring changes in length, in particular for use in a six-axis force-torque sensor, which is able to achieve a high resolution of the measurement signal due to its high stiffness. [Means for solving the problem]

[0004] The above problem is solved by a device for measuring changes in length with the features of claim 1. Advantageous embodiments and further developments of the invention are set forth in the dependent claims.

[0005] A device for measuring changes in length according to the present invention includes a first fixed element, a second fixed element, and at least one length element disposed between the two fixed elements, the at least one length element having a first end, a second end, and a length along the longitudinal direction. A force acting parallel to the longitudinal direction causes a change in the length of the at least one length element. In such a device, a lever element has a first end, a second end, and a fulcrum and is disposed transverse to the longitudinal direction. The lever element includes a first lever arm and a second lever arm, the first lever arm having a first length between the fulcrum and the first lever arm end, and the second lever arm having a second length between the fulcrum and the second lever arm end, the second length being greater than the first length. The at least one length element has a first end pivotally disposed on the first lever arm end of the first lever arm. The second lever arm end of the second lever arm is connected to a material measuring unit, and its movement is detectable by a scanning element.

[0006] In other words, the basic idea of ​​the present invention is to mechanically amplify the change in length by means of a lever element and detect the path change at the free end of the longer lever arm. This type of mechanical amplification is simple and inexpensive to implement. It can be used in particular for systems with high stiffness, and despite the stiffness, the mechanical amplification allows a high resolution of the change in length caused by a force or moment to be achieved.

[0007] In a preferred embodiment of the invention, the fulcrum is located between the first and second ends of the lever element, with the first lever arm end of the first lever arm forming the first end of the lever element and the second lever arm end of the second lever arm forming the second end of the lever element, thus forming a double-sided lever.

[0008] In an alternative preferred embodiment of the present invention, the fulcrum is located at the first end of the lever element, thus forming a single-sided lever. A preferred further development of the invention provides a second element having a first end and a second end and arranged parallel to the lever element by a first arm and a second arm aligned parallel to one another. This arrangement is pivotable between the second element and the first arm, between the second element and the second arm, between the lever element and the first arm, and between the lever element and the second arm. In this way, a parallelogram is formed, which allows the material measuring part arranged at the second arm end of the second lever arm to be inclined relative to the scanning element when the lever element is pivoted without the second element, and to be guided in alignment parallel to the longitudinal direction when the lever element is pivoted by the second element.

[0009] Preferably, the material measuring part is arranged on the second arm and preferably extends over the distance between the lever element and the second element, so that upon pivoting of the lever element the material measuring part can be aligned in any position parallel to the longitudinal direction.

[0010] Good stability of the lever arrangement can preferably be achieved when the first arm is arranged between the fulcrum and the first end of the second element, and the second arm is arranged between the second end of the lever element and the second end of the second element.

[0011] In a particularly preferred embodiment of the invention, the pivotable connection is in the form of a film hinge. Even with very stiff materials, such a pivotable connection can easily be formed by weakened material regions, so that on the one hand it does not affect or only minimally affects the desired high stiffness of the length element, and on the other hand the desired high resolution can be achieved by mechanical reinforcement via the lever arrangement.

[0012] Preferably, the first fixation element is disc-shaped with a first plane and the second fixation element is disc-shaped with a second plane, the first and second planes being arranged parallel to each other and the longitudinal direction preferably being perpendicular to these planes. The disc-shaped design of the fixation elements allows for good fixation to components that move relative to each other and allows for measurement of forces and moments occurring therebetween.

[0013] The placement of the plane perpendicular to the longitudinal direction can facilitate measurement of applied forces and moments. In a particularly preferred embodiment, several, in particular at least six, e.g., precisely six length elements are arranged between the first and second fixing elements, which allows for measuring forces and moments acting in three axes between the two fixing elements, thus forming a six-axis force-torque sensor.

[0014] Advantageously, the scanning element is implemented as an optical, capacitive, inductive or magnetic scanning sensor, optical sensors in particular being very robust and allowing high resolution scanning. Preferably, an evaluation unit is provided which evaluates the signals detected by the at least one scanning element and in particular calculates the forces and moments exerted between the two fixation elements due to the change in length.

[0015] The present invention will now be described in detail with reference to the following figures. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows a perspective view of a first embodiment of a device for measuring changes in length according to the invention; [Figure 2] 2 shows a further perspective view of a part of the device according to FIG. 1; [Figure 3] 3 shows a longitudinal section of the device according to FIG. 2. [Figure 4] 2 shows a schematic diagram of the lever arrangement of the device according to FIG. 1; [Figure 5]10 shows a schematic diagram of a lever arrangement of an alternative embodiment of a device for measuring changes in length. [Figure 6] 2 shows a perspective view of an apparatus for measuring changes in length using six length elements according to FIG. 1 to form a six-axis force-torque sensor; DETAILED DESCRIPTION OF THE INVENTION

[0017] 1-4 show different views of a first embodiment of an apparatus 10 according to the present invention for measuring a change in length ΔL relative to a length element 15. The length element has a first end 15a, a second end 15b, and a length L along a longitudinal direction R. A force F acting parallel to the longitudinal direction R results in a change in length ΔL of the length element 15. Direct measurement of this change in length ΔL relative to the length element 15 is often expensive or can only be detected with low resolution because the change in length ΔL is so small. Accordingly, the illustrated apparatus 10 includes a lever element 20 disposed transverse to the longitudinal direction R and having a first end 20a, a second end 20b, and a fulcrum D. The lever element 20 has a first lever arm 21 and a second lever arm 22. The first lever arm 21 has a first length a between the fulcrum D and the first lever arm end 21a, and the second lever arm 22 has a second length b between the fulcrum D and the second lever arm end 22b. The second length b is configured to be greater than the first length a. The length element 15 has its first end 15a pivotably arranged on the first lever arm end 21a of the first lever arm 21, while the second lever arm end 22b of the second lever arm 22 is connected to the material measuring unit 30. The pivotable arrangement between the length element 15 and the first lever arm end 21a of the first lever arm 21 can also be realized, in particular, in the form of a film hinge. The film hinge can be formed, for example, by a weakened material region.

[0018] The apparatus 10 further comprises a scanning element 40 capable of detecting movement of the material measuring portion 30 . A force F acting on the length element 15 parallel to the longitudinal direction R and resulting in a change in length ΔL at the lever arm end 21a of the short lever arm 21 causes a change in path Δs at the second lever arm end 22b of the long lever arm 22 by the lever element 20. The change in length ΔL is then amplified in particular in the ratio b:a and thus at the second lever arm end 22b. route The change Δs in is Δs=b*ΔL / a.

[0019] The change in path Δs is detected by a scanning element 40 which scans the material measuring part 30 connected to the second lever arm end 22b. The material measuring part 30 can in particular be scanned optically, for which purpose, for example, the material measuring part 30 can be embodied so as to be reflective.

[0020] 1 to 4, in this embodiment, a double-sided lever is formed with a fulcrum D disposed between the first end 20a and the second end 20b of the lever element 20. In this way, the first lever arm end 21a of the first lever arm 21 particularly forms the first end 20a of the lever element 20, and the second lever arm end 22b of the second lever arm 22 particularly forms the second end 20b of the lever element 20.

[0021] As shown in Figure 5, a fulcrum D can be located at a first end 20a of a lever element 20. This forms a single-sided lever. Two lever arms 21, 22 extend in the same direction from the fulcrum D, but have different lengths a or alternatively lengths b.

[0022] The material measuring part 30 can be arranged in front of the lever element 20. The scanning element 40 is aligned towards the end face of the second lever arm end 22b so as to be able to scan the material measuring part. In this case, the scanning element 40 is particularly rigidly fixed, in particular parallel to the longitudinal direction R and fixed relative to the length element 15. However, when the lever element 20 moves, the material measuring part 30 rotates about the fulcrum D along a circular path, which can distort the measurement signal of the scanning element 40.

[0023] Therefore, regardless of whether the lever element is implemented as a single-sided or double-sided lever, it is preferable to provide a second element 50 having a first end 50a and a second end 50b, and the second element is preferably arranged parallel to the lever element by a first arm 51 having a first end 51a and a second end 51b and a second arm 52 having a first end 52a and a second end 52b. The first end 51a of the first arm 51 is in particular connected to the fulcrum D of the lever element 20, and the second end 51b of the first arm 51 is connected to the first end 20a of the second element 50. Meanwhile, the first end 52a of the second arm 52 is connected to the second end 20b of the lever element 20, and the second end 52b of the second arm 52 is connected to the second end 50b of the second element 50. In this case, the arrangements between the second element 50 and the first arm 51, between the second element 50 and the second arm 52, between the lever element 20 and the first arm 51, and between the lever element 20 and the second arm 52 are implemented so as to be pivotable, in particular in the form of film hinges, which can be formed, for example, by weakened material regions.

[0024] The material measuring part 30 is arranged on the second arm 52, and preferably the material measuring part may extend over the distance between the lever element 20 and the second element. With this arrangement, the material measuring part 30 remains connected to the lever element 20, but preferably pivotally, so that when the lever element 20 moves due to the force F acting on the length element 15, the material measuring part 30 continues to move according to the transmission ratio. However, the guidance of the second element causes a translational movement such that the material measuring part 30 maintains its orientation relative to the scanning element 40 as it moves.

[0025] The scanning element 40 may include or be connected to an evaluation unit 60 which evaluates the signals detected by the scanning element 40 and in particular calculates the force F acting on the length element 15 from the change in the measured length Dl.

[0026] In order to enable the scanning element 30 to be fixedly positioned relative to the length element 15, two cross members 17a, 17b are arranged at the first end 15a and the second end 15b of the length element 15, which cross members are guided over and engage around the lever arrangement formed by the lever element and optionally the second element and the two arms 51, 52, in particular on both sides, so that the scanning element is positioned at the end of the cross members 17a, 17b facing away from the length element 15.

[0027] To be able to measure the change in length ΔL when a force is applied between the two components, length element 15 is connected at its first end 15a to first fixation element 11 and at its second end 15b to second fixation element 12. If first fixation element 11 is connected to a first component (not shown) and second fixation element 12 is connected to a second component (not shown), it is possible to measure the force applied when the two components move relative to each other. First fixation element 11 may be formed by first cross member 17a and second fixation element 12 may be formed by second cross member 17b.

[0028] FIG. 6 shows a perspective view of a device 10′ for measuring a change in length ΔL, which includes six length elements 15 according to the example embodiment shown in FIGS. 1 to 4. In this case, the device 10′ includes a first fixing element 11′ and a second fixing element 12′, with the cross members 17a of the six length elements 15 connected to the first fixing element 11′ and the cross members 17b of the six length elements 15 connected to the second fixing element 12′. The fixing elements 11′, 12′ are formed in a disk-like, e.g., disk-ring-like, manner with a first plane E1 or alternatively a second plane E2, which are arranged parallel to each other and, in particular, perpendicular to the longitudinal direction R of the length elements 15. The length elements 15 are uniformly distributed around the circumference of the fixing elements 11′, 12′, forming, in particular, a six-axis force-torque sensor. For this purpose, the signals detected by all six scanning elements 40 are sent to an evaluation unit 60, from which the forces Fx, Fy, Fz and moments Mx, My, Mz applied between the two fixing elements 11', 12' can be calculated by appropriate calibration. [Explanation of symbols]

[0029] 10...device, 10'...device, 11, 11'...first fixing element, 12, 12'...second fixing element, 15...length element, 15a...first end, 15b...second end, 20...lever element, 20a...first end, 20b...second end, 21...first lever arm, 21a...first lever arm end, 22...second lever arm, 22a...second lever arm end, 30...material measuring unit, 40...scanning element, 50...second element, 50a...first end, 50b...second end, 51...first arm, 51a...first end, 51b...second end, 52...second arm, 52a...first end, 52b...second end, 60...evaluation unit, L...length, ΔL...change in length, R...longitudinal direction, F...force, M...moment, D...fulcrum, s...path, Δs...change in path, a...first length, b...second length, E1...first plane, E2...second plane.

Claims

1. A device (10, 10') for measuring a change in length (ΔL), comprising: A device comprising a first fixing element (11'), a second fixing element (12'), and at least two length elements (15) arranged between the two fixing elements (11', 12'), the at least two length elements (15) having a first end (15a), a second end (15b), and a length (L) along a longitudinal direction (R), wherein a force (F) acting parallel to the longitudinal direction (R) causes a change in length (ΔL) of the at least two length elements (15), a lever element (20) having a first end (20a), a second end (20b), and a fulcrum (D) disposed transversely to a longitudinal direction (R); The lever element (20) has a first lever arm (21) and a second lever arm (22), the first lever arm (21) having a first length (a) between a fulcrum (D) and a first lever arm end (21a), and the second lever arm (22) having a second length (b) between the fulcrum (D) and a second lever arm end (22b); the second length (b) is greater than the first length (a); At least two length elements (15) have their first ends (15a) pivotally arranged on the first lever arm end (21a) of the first lever arm (21); a second lever arm end (22b) of the second lever arm (22) is connected to a material measuring portion (30), and movement of the material measuring portion (30) is detectable by a scanning element (40); At least two length elements (15) are arranged between the first fixing element (11') and the second fixing element (12'); and providing an evaluation unit (60) for evaluating the signals detected by at least one scanning element (40) and for calculating the forces and moments exerted between the two fixation elements due to the change in length.

2. 2. The device according to claim 1, characterized in that the fulcrum (D) is arranged between the first end (20a) and the second end (20b) of the lever element (20), the first lever arm end (21a) of the first lever element (21) forming the first end (20a) of the lever element (20) and the second lever arm end (22b) of the second lever arm (22) forming the second end (20b) of the lever element (20).

3. 3. The device according to claim 1 or 2, characterized in that the second element (50) has a first end (50a) and a second end (50b) and is arranged parallel to the lever element (20) with a first arm (51) and a second arm (52) aligned parallel to each other, said arrangement being pivotable between the second element (50) and the first arm (51), between the second element (50) and the second arm (52), between the lever element (20) and the first arm (51), and between the lever element (20) and the second arm (52).

4. 4. Device according to claim 3, characterized in that the material measuring part (30) is arranged on the second arm (52).

5. 4. Device according to claim 3, characterized in that the material measuring part (30) extends over the distance between the lever element (20) and the second element (50).

6. 6. The device according to claim 3, wherein the first arm (51) is arranged between the fulcrum (D) and the first end (50a) of the second element (50), and the second arm (52) is arranged between the second end (20b) of the lever element (20) and the second end (50b) of the second element (50).

7. 7. Device according to any one of claims 1 to 6, characterized in that the pivotable connection is implemented in the manner of a film hinge.

8. 8. Device according to any one of claims 1 to 7, characterized in that the first fixing element (11') is disc-shaped with a first plane (E1) and the second fixing element (12') is disc-shaped with a second plane (E2), the first plane (E1) and the second plane (E2) being arranged parallel to each other.

9. 8. A device according to any one of claims 1 to 7, characterized in that the first fixing element (11') is disc-shaped with a first plane (E1) and the second fixing element (12') is disc-shaped with a second plane (E2), the first plane (E1) and the second plane (E2) being arranged parallel to one another and the longitudinal direction (R) being perpendicular to these planes (E1, E2).

10. Device according to any one of the preceding claims, characterized in that the scanning element (40) is configured as an optical, capacitive, inductive or magnetic scanning sensor.

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