DEVICE FOR MEASURING A CHANGE IN LENGTH

Description

[0001] The invention relates to a device for measuring a change in length according to the preamble of patent claim 1.

[0002] In automation technology, 6-axis force-torque sensors are widely used to determine the forces and torques acting in all directions. For example, such sensors can be used in the automatic joining or assembly of workpieces, in deburring, polishing or grinding, in haptic measurements, or in other applications. These sensors measure the forces (Fx, Fy, Fz) and torques (Mx, My, Mz) acting on them in and around three coordinates (x, y, z). On the one hand, such sensors should be as rigid as possible so that they themselves are not deformed by the forces or torques. On the other hand, the highest possible resolution of the measured signals should be achieved, which is generally not possible with rigid sensors. In existing sensors, strain gauges are used to determine the forces and torques, with which very small material strains can be measured.However, applying the strain gauges is very complex. Furthermore, strain gauges require high signal amplification, which leads to the high cost of such 6-axis force-torque sensors. US Pat. No. 4,544,858 describes a device used to measure weights using frequency measurement.

[0003] The object of the invention is therefore to provide a device for measuring a change in length, in particular for use in 6-axis force-torque sensors, which can achieve a high resolution of the measured signals with a high rigidity.

[0004] The object is achieved according to the invention by a device for measuring the change in length with the features of patent claim 1.

[0005] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0006] The device according to the invention for measuring a change in length with a first fastening element, a second fastening element and at least one length element arranged between the two fastening elements with a first end, a second end and a length along a longitudinal direction, wherein a force acting parallel to the longitudinal direction leads to a change in the length of the length element, is characterized in that a lever element with a first end, a second end and a pivot point is arranged transversely to the longitudinal direction, wherein the lever element has a first lever arm with a first length between the pivot point and a first lever arm end and a second lever arm with a second length between the pivot point and a second lever arm end, wherein the second length is designed to be greater than the first length,that the length element is pivotably arranged with its first end on the first lever arm end of the first lever arm and wherein the second lever arm end of the second lever arm is connected to a measuring embodiment whose movement can be detected by a scanning element.,

[0007] In other words, the basic idea of ​​the invention is to mechanically amplify the length change using a lever element and to detect the change in displacement at the free end of the longer lever arm. Such mechanical amplification is simple and cost-effective to implement. It can be used particularly in systems with high rigidity, where, despite the high rigidity, the mechanical amplification allows for a high resolution of the length change caused by a force or torque.

[0008] In a preferred embodiment of the invention, the pivot point is arranged between the first end and the second end of the lever element, and the first lever arm end of the first lever arm forms the first end of the lever element, while the second lever arm end of the second lever arm forms the second end of the lever element. In this way, a two-sided lever is formed.

[0009] In an alternative preferred embodiment of the invention, the pivot point is located at the first end of the lever element. This forms a one-sided lever.

[0010] A preferred development of the invention provides that a second element, which has a first end and a second end and which is arranged parallel to the lever element by means of a first arm and a second arm which are aligned parallel to one another, wherein the 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 makes it possible to guide the mass embodiment arranged at the second lever arm end of the second lever arm, which mass embodiment without the second element tilts against the scanning element during a pivoting movement of the lever element, aligned parallel to the longitudinal direction during a pivoting movement of the lever element by the second element.

[0011] Preferably, the mass is arranged on the second arm, preferably extending over the distance between the lever element and the second element. This allows the mass to be arranged in any position parallel to the longitudinal direction during a pivoting movement of the lever element.

[0012] Good stability of the lever arrangement can be achieved if preferably the first arm is arranged between the pivot point 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.

[0013] A particularly preferred embodiment of the invention provides for the pivotable connections to be designed in the manner of a film hinge. Such pivotable connections can be easily formed by weakening the material, even in materials with high rigidity, so that, on the one hand, the desired high rigidity of the linear element is not or only slightly impaired, while, on the other hand, the desired high resolution can be achieved through the mechanical reinforcement provided by the lever arrangement.

[0014] Preferably, the first fastening element is disk-shaped with a first plane, and the second fastening element is disk-shaped with a second plane, wherein the first plane and the second plane are arranged parallel to one another, and preferably the longitudinal direction is perpendicular to the planes. The disk-shaped design of the fastening elements enables good attachment to the components that are to be moved relative to one another, between which the forces and torques occurring are to be measured.

[0015] The arrangement of the planes perpendicular to the longitudinal direction can simplify the determination of the acting forces and torques.

[0016] A particularly preferred embodiment provides for several, in particular at least six, for example exactly six, longitudinal elements to be arranged between the first fastening element and the second fastening element. This enables the determination of the forces and torques acting between the two fastening elements in and around three axes, thus enabling the design as a 6-axis force-torque sensor.

[0017] Advantageously, the sensing element is designed as an optical, capacitive, inductive, or magnetic sensor. Optical sensors, in particular, are particularly robust and enable high-resolution sensing.

[0018] 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 torques acting between the two fastening elements from the determined length changes.

[0019] The invention is explained in detail with reference to the following figures. Figure 1 shows a perspective view of a first embodiment of a device according to the invention for measuring a change in length, Figure 2 shows a further perspective view of a part of the device according to Figure 1 , Figure 3 a longitudinal section through the device according to Figure 2 , Figure 4 a schematic representation of the lever arrangement of the device according to Figure 1 , Figure 5 is a schematic representation of a lever arrangement of an alternative embodiment of a device for measuring a change in length and Figure 6 is a perspective view of a device for measuring a change in length with six length elements according to Figure 1 to form a 6-axis force-torque sensor.

[0020] The Figures 1 to 4show various views of a first embodiment of a device 10 according to the invention for measuring a change in length ΔL on a length element 15, which 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 leads to a change in length ΔL of the length element 15. A direct measurement of this change in length ΔL on the length element 15 is complex or can often only be recorded with low resolution due to the small change in length ΔL.The device 10 shown therefore comprises a lever element 20 arranged transversely to the longitudinal direction R, having a first end 20a, a second end 20b, and a pivot point D. The lever element 20 has a first lever arm 21 with a first length a between the pivot point D and a first lever arm end 21a, and a second lever arm 22 with a second length b between the pivot point D and a second lever arm end 22b. The second length b is greater than the first length a, and the longitudinal element 15 is arranged with its first end 15a pivotably 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 a measuring embodiment 30. The pivotable arrangement between the longitudinal element 15 and the first lever arm end 21a of the first lever arm 21 can, in particular, be designed in the manner of a film hinge.The film hinge can, for example, be formed by a weakening of the material.

[0021] The device 10 further comprises a scanning element 40 which detects a movement of the measuring embodiment 30.

[0022] A force F acting parallel to the longitudinal direction R on the length element 15 and causing 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 due to the lever element 20. In particular, the change in length ΔL is amplified in the ratio b:a, the change in length Δs at the second lever arm end 22b is thus Δs = b * ΔL / a

[0023] The displacement change Δs is detected by the scanning element 40, which scans the measuring element 30 connected to the second lever arm end 22b. In particular, the measuring element 30 can be scanned optically, for which purpose, for example, the measuring element 30 can be designed to be reflective.

[0024] As in the Figures 1 to 4 As shown, the pivot point D in this embodiment is arranged between the first end 20a and the second end 20b of the lever element 20, forming a two-sided lever. In particular, the first lever arm end 21a of the first lever arm 21 forms the first end 20a of the lever element 20, and the second lever arm end 22b of the second lever arm 22 forms the second end 20b of the lever element 20.

[0025] As in Figure 5 As shown, it is possible for the pivot point D to be located at the first end 20a of the lever element 20. This creates a one-sided lever. The two lever arms 21, 22 extend from the pivot point D in the same direction, but with different lengths a and b, respectively.

[0026] The measuring scale 30 can be arranged on the end face of the lever element 20. The scanning element 40 is oriented such that it points toward the end face of the second lever arm end 22b in order to scan the measuring scale. In this case, the scanning element 40 is rigidly fixed, in particular parallel to the longitudinal direction R and rigid relative to the length element 15. However, upon movement of the lever element 20, the measuring scale 30 pivots around the pivot point D on a circular path, which can lead to corrupted measurement signals in the scanning element 40.

[0027] Therefore, regardless of whether the lever element is designed as a one-sided or two-sided lever, a second element 50 is preferably provided which has a first end 50a and a second end 50b and which is arranged parallel to the lever element by means of a first arm 51 which has a first end 51a and a second end 51b and a second arm 52 which is aligned parallel to the first arm 51 and has a first end 52a and a second end 52b. In particular, the first end 51a of the first arm 51 is connected to the pivot point 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, while 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.The arrangements between the second element 50 and the first arm 51, the second element 50 and the second arm 52, the lever element 20 and the first arm 51, and between the lever element 20 and the second arm 52 are pivotable, in particular in the manner of a film hinge. The film hinge can be formed, for example, by a weakened material.

[0028] The mass embodiment 30 can be arranged on the second arm 52 and preferably extend over the distance between the lever element 20 and the second element 50. This arrangement ensures that the mass embodiment 30 remains connected to the lever element 20, but preferably pivotably, so that when the lever element 20 moves due to a force F acting on the length element 15, the mass embodiment 30 continues to move in accordance with the transmission ratio, but the guidance of the second element causes a parallel displacement, so that the mass embodiment 30 remains aligned relative to the scanning element 40 during its movement.

[0029] The scanning element 40 may comprise an evaluation unit 60 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 determined length changes Dl.

[0030] In order to be able to arrange the scanning element 30 rigidly relative to the longitudinal element 15, two cross members 17a, 17b are arranged on the longitudinal element 15 at the first end 15a and the second end 15b, which cross members 17a, 17b are guided past the lever arrangement formed by the lever element and optionally the second element and the two arms 51, 52, in particular encompassing them on both sides, so that the scanning element can be arranged at the ends of the cross members 17a, 17b facing away from the longitudinal element 15.

[0031] In order to determine the change in length DL when a force acts between two components, the length element 15 is connected at its first end 15a to a first fastening element 11 and at its second end 15b to a second fastening element 12. If the first fastening element 11 is connected to a first component (not shown) and the second fastening element 12 is connected to a second component (not shown), the forces acting upon movement of the two components relative to one another can be determined. The first fastening element 11 can be formed by the first cross member 17a, and the second fastening element 12 can be formed by the second cross member 17b.

[0032] Figure 6 shows a perspective view of a device 10' for measuring a change in length ΔL, which comprises six length elements 15 according to the method shown in the Figures 1 to 4illustrated embodiment. The device 10' has a first fastening element 11' and a second fastening element 12', wherein the cross members 17a of the six longitudinal elements 15 are connected to the first fastening element 11' and the cross members 17b of the six longitudinal elements 15 are connected to the second fastening element 12'. The fastening elements 11', 12' are disc-like, for example disc-ring-like, with a first plane E1 and a second plane E2, respectively, wherein the planes E1 and E2 are arranged parallel to one another and in particular perpendicular to the longitudinal direction R of the longitudinal elements 15. The longitudinal elements 15 are arranged uniformly distributed over the circumference of the fastening elements 11', 12' and in particular form a 6-axis force-torque sensor.For this purpose, the signals detected by all six scanning elements 40 are fed to the evaluation unit 60, from which the forces Fx, Fy, Fz and torques Mx, My, Mz acting between the two fastening elements 11', 12' can be calculated with appropriate calibration. List of reference symbols

[0033] 10Device 10'Device 11, 11'First fastening element 12, 12'Second fastening element 15Length element 15aFirst end 15bSecond end 20Lever element 20aFirst end 20bSecond end 21First lever arm 21aFirst lever arm end 22Second lever arm 22aSecond lever arm end 30Measuring standard 40Scanning element 50Second element 50aFirst end 50bSecond end 51First arm 51aFirst end 51bSecond end 52Second arm 52aFirst end 52bSecond end 60Evaluation unit LLength ΔLLength change RLongitudinal direction FForce MTorque DPivot point sDistance ΔsDistance change aFirst length or side length E1First plane E2Second plane

Claims

1. Device (10, 10') for measuring a length change (ΔL), comprising a first fastening element (11, 11'), a second fastening element (12, 12'), and at least one length element (15) that is arranged between the two fastening elements (11, 11', 12, 12') and has a first end (15a), a second end (15b) and a length (L) along a length direction (R), wherein a force (F) acting in parallel with the length direction (R) leads to a length change (ΔL) of the length element (15), characterised in that a lever element (20) having a first end (20a), a second end (20b) and a fulcrum (D) is arranged transversely to the length direction (R), wherein the lever element (20) comprises a first lever arm (21) of a first length (a) between the fulcrum (D) and a first lever arm end (21a), and a second lever arm (22) of a second length (b) between the fulcrum (D) and a second lever arm end (22b), wherein the second length (b) is greater than the first length (a), wherein the length element (15) is arranged with its first end (15a) pivotably on the first lever arm end (21a) of the first lever arm (21), and wherein the second lever arm end (22b) of the second lever arm (22) is connected to an material measure(30), wherein the device (10) comprises a scanning element (40) which detects the movement of the material measure(30).

2. Device according to any of the preceding claims, characterised in that the fulcrum (D) is arranged between the first end (20a) and the second end (20b) of the lever element (20), and the first lever arm end (21a) of the first lever arm (21) forms the first end (20a) of the lever element (20), and the second lever arm end (22b) of the second lever arm (22) forms the second end (20b) of the lever element (20).

3. Device according to any of the preceding claims, characterised in that the fulcrum (D) is arranged at the first end (20a) of the lever element (20).

4. Device according to any of the preceding claims, characterised in that a second element (5) which comprises a first end (50a) and a second end (50b) and which is arranged in parallel with the lever element (20) by means of a first arm (51) and a second arm (52) oriented in parallel with one another, wherein the arrangement is 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 (30) and the first arm (51), and between the lever element (20) and the second arm (52).

5. Device according to any of the preceding claims, characterised in that the material measure(30) is arranged on the second arm (52) and preferably extends over the spacing between the lever element (20) and the second element (50).

6. Device according to any of the preceding claims, characterised in that 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 (50bb) of the second element (50).

7. Device according to any of the preceding claims, characterised in that the pivotable connections are formed in the manner of a film hinge.

8. Device according to any of the preceding claims, characterised in that the first fastening element (11, 11') is configured in a wafer-like manner having a first plane (E1), and the second fastening element (12, 12') is configured in a wafer-like manner having a second plane (E2), wherein the first plane (E1) and the second plane (E2) are arranged in parallel with one another and the length direction (R) is preferably arranged perpendicularly to the planes (E1, E2).

9. Device according to any of the preceding claims, characterised in that a plurality of, in particular six, length elements (15) are arranged between the first fastening element (11') and the second fastening element (12').

10. Device according to any of the preceding claims, characterised in that the scanning element (40) is configured as an optically, capacitively, inductively or magnetically scanning sensor.

11. Device according to any of the preceding claims, characterised in that an evaluation unit (60) is provided, which evaluates the signals detected by the at least one scanning element (40), and in particular calculates the forces and torques acting between the two fastening elements, from the determined length changes.