Performance testing device for micro-torque precision speed reducer

Abstract

The utility model provides a micro-torque precision speed reducer performance testing device, and belongs to the technical field of speed reducer performance testing. Comprising a first installation support body, a tested piece support body, a second installation support body and a load support body which are horizontally and longitudinally arranged on a workbench base in sequence, a tested speed reducer is detachably installed on the tested piece support body, and a first torque sensor and a first grating angle encoder are arranged on the first installation support body side by side; the input end of the first torque sensor and the input end of the first grating angle encoder are connected with a first servo drive motor and a second servo drive motor respectively, and a second torque sensor and a second grating angle encoder are arranged on the second installation support side by side. And a load motor connected with the second torque sensor is arranged on the load bracket body. When transmission error detection is carried out, the second grating angle encoder is independently connected with the tested speed reducer, the friction torque influence of the torque sensor is eliminated, and the effect of improving the test precision of the tested speed reducer is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of speed reducer performance testing, in particular to a micro-torque precision speed reducer performance testing device. Background Art

[0002] Industrial robots are widely used in the fields of automobiles, aerospace, electronics, food, new energy, etc. Harmonic reducers are currently one of the most widely used reduction devices in industrial robot joints. Harmonic reducers have the advantages of large speed ratio, smooth movement, simple structure and high efficiency. They are joint reduction devices with superior performance. When manufacturing harmonic reducers, it is necessary to test the performance of harmonic reducers.

[0003] The patent with announcement number CN209910970U discloses a harmonic reducer test mechanism, including a base plate, a motor support, an input torque support, an input angular support, a harmonic reducer support, an output angular support, an output torque support, a magnetic powder brake, a servo motor, an input torque sensor, an input angular displacement sensor, an output angular displacement sensor and an output torque sensor. More performance data of the harmonic reducer can be tested at the same time, such as torque, load, rigidity, repeated positioning error and backlash performance data.

[0004] In the field of tiny signal harmonic reducers, due to the characteristics of small size, high precision and very small torque, ordinary reducer testing equipment is difficult to meet the installation of tiny reducers and the testing requirements of their tiny torque. Therefore, it is necessary to design a device that can be used for performance testing of tiny torque precision reducers based on the test difficulties. Utility Model Content

[0005] In view of the above problems, the utility model provides a micro-torque precision reducer performance testing device.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the utility model is as follows:

[0007] Provided is a micro-torque precision reducer performance test device, comprising a workbench base, on which a first mounting bracket body, a test piece bracket, a second mounting bracket body and a load bracket body are arranged in sequence horizontally and vertically, and a test piece bracket body can be detachably mounted with a test reducer;

[0008] A first torque sensor and a first grating angle encoder are arranged side by side on the first mounting bracket body, an input end of the first torque sensor and an input end of the first grating angle encoder are respectively connected to a first servo drive motor and a second servo drive motor, and a driving transverse feed system for alternately aligning the first torque sensor and the first grating angle encoder with the reducer under test, and a driving longitudinal feed system for making the first mounting bracket body approach / move away from the test piece bracket are arranged on the workbench base;

[0009] A second torque sensor and a second grating angle encoder are arranged side by side on the second mounting bracket body, a load bracket body is arranged on the second mounting bracket body, a load motor connected to the second torque sensor is arranged on the load bracket body, a load lateral feed system for alternately aligning the second torque sensor and the second grating angle encoder with the reducer under test, and a load longitudinal feed system for making the second mounting bracket body approach / move away from the test piece bracket are arranged on the workbench base.

[0010] Further, the driving transverse feed system includes a first sliding seat, a first handle and a first screw rod, the first sliding seat is horizontally and transversely slidably arranged on the workbench base, the first screw rod is horizontally and transversely arranged and rotatably connected to the workbench base, the first handle is connected to one end of the first screw rod, and the first screw rod is threadedly connected to the first sliding seat;

[0011] The driving longitudinal feed system includes a second handle and a second screw rod. The first mounting bracket body is arranged on the first sliding seat along the horizontal longitudinal sliding direction. The second screw rod is arranged along the horizontal longitudinal direction and is rotatably connected to the first sliding seat. The second screw rod is threadedly connected to the first mounting bracket body. The second handle is rotatably connected to the first sliding seat and is transmission connected to the second screw rod.

[0012] Further, the load lateral feeding system comprises a second sliding seat, a third handle and a third screw rod, the second sliding seat is horizontally and laterally slidably arranged on the workbench base, the third screw rod is horizontally and laterally arranged and rotatably connected to the workbench base, the third handle is connected to one end of the third screw rod, and the third screw rod is threadedly connected to the second sliding seat;

[0013] The load longitudinal feeding system includes a fourth handle and a fourth screw. The second mounting bracket body is arranged on the second sliding seat along the horizontal longitudinal sliding, the fourth screw is arranged along the horizontal longitudinal and is rotatably connected to the second sliding seat, the fourth screw is threadedly connected to the second mounting bracket body, and the fourth handle is rotatably connected to the first sliding seat and is transmission connected to the fourth screw.

[0014] Further, the load motor includes a first load servo motor and a second load servo motor arranged side by side, the first load servo motor and the second load servo motor have different powers, and the second mounting bracket body is provided with a transposition lateral feed system for driving the first load servo motor and the second load servo motor to alternately align with the second torque sensor, and a transposition longitudinal feed system for making the load bracket body approach / move away from the second mounting bracket body;

[0015] The transposition lateral feeding system comprises a third sliding seat, a fifth handle and a fifth screw rod, the third sliding seat is horizontally and laterally slidably arranged on the second mounting bracket body, the fifth screw rod is horizontally and laterally arranged and rotatably connected to the second mounting bracket body, the fifth handle is connected to one end of the fifth screw rod, and the fifth screw rod is threadedly connected to the third sliding seat;

[0016] The transposition longitudinal feed system includes a sixth handle and a sixth screw rod. The load bracket body is set on the third sliding seat along the horizontal longitudinal sliding direction. The sixth screw rod is set along the horizontal longitudinal direction and is rotatably connected to the third sliding seat. The sixth screw rod is threadedly connected to the sixth mounting bracket body. The sixth handle is rotatably connected to the third sliding seat and is transmission connected to the sixth screw rod.

[0017] Furthermore, the first sliding seat, the driving bracket body, the second sliding seat, the second bracket body, the third sliding seat and the load bracket body are all provided with a manual locking mechanism for limiting their own sliding.

[0018] Furthermore, a brake and a third torque sensor are sequentially connected between the second servo drive motor and the first grating angle encoder.

[0019] The beneficial effects of the utility model are as follows: by arranging the first grating angle encoder and the first torque sensor and the second grating angle encoder and the second torque sensor side by side, when performing a transmission error test on a micro-torque precision reducer, the driving end and the output end of the reducer to be tested are respectively connected to the first grating angle encoder and the second grating angle encoder, and the second grating angle encoder directly detects and obtains the tiny torque at the output end of the reducer to be tested, thereby avoiding the friction torque of the torque sensor affecting the rigid deformation of the micro reducer and improving the test accuracy of the micro-torque precision reducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the overall structure of the micro-torque precision reducer performance testing device according to an embodiment of the present application.

[0021] Figure 2 This is a front structural schematic diagram of the micro-torque precision reducer performance testing device according to an embodiment of the present application.

[0022] Figure 3It is a left view schematic diagram of the micro-torque precision reducer performance testing device according to an embodiment of the present application.

[0023] Figure 4 It is a right view schematic diagram of the micro-torque precision reducer performance testing device according to an embodiment of the present application.

[0024] Among them, 1. workbench base; 11. first mounting bracket body; 12. measured piece bracket; 13. second mounting bracket body; 10. measured reducer; 21. first torque sensor; 22. first grating angle encoder; 23. first servo drive motor; 24. second servo drive motor; 25. drive lateral feed system; 26. drive longitudinal feed system; 27. first sliding seat; 31. second torque sensor; 32. second grating angle encoder; 33. load lateral feed system; 34. load longitudinal feed system; 35. second sliding seat; 41. load bracket body; 42. first load servo motor; 43. second load servo motor; 44. transposition lateral feed system; 45. transposition longitudinal feed system; 46. third sliding seat; 5. manual locking mechanism; 6. brake; 7. third torque sensor. DETAILED DESCRIPTION

[0025] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0026] The present application discloses a micro-torque precision reducer performance test device, referring to Figure 1 , Figure 2 , Figure 3 and Figure 4 , including a workbench base 1, on which a first mounting bracket body 11, a test piece bracket 12, a second mounting bracket body 13 and a load bracket body 41 are sequentially arranged from right to left along the horizontal longitudinal direction. The test piece bracket 12 is used to install the test reducer 10. Specifically, a plurality of mounting holes are arranged at intervals along the horizontal lateral direction on the test piece bracket 12, and a flange mold can be detachably mounted at the mounting holes by bolts. The test reducer 10 is mounted on the flange mold. By replacing flange molds of different sizes, different types of test reducers 10 can be installed in the mounting holes.

[0027] The first torque sensor 21 and the first grating angle encoder 22 are installed side by side horizontally on the first mounting bracket body 11, and the output ends of the first torque sensor 21 and the first grating angle encoder 22 are both at the same height as the axis of the mounting hole on the measured object bracket 12. The first servo drive motor 23 and the second servo drive motor 24 are also fixedly installed side by side on the edge of the first mounting bracket body 11 away from the measured bracket body, and the first servo drive motor 23 and the second servo drive motor 24 are connected to the input shafts of the first torque sensor 21 and the first grating angle encoder 22 respectively.

[0028] A driving lateral feed system 25 is arranged on the workbench base 1 for alternately aligning the first torque sensor 21 and the first grating angle encoder 22 with the measured reducer 10. The driving lateral feed system 25 includes a first sliding seat 27, a first handle and a first screw. The first sliding seat 27 is horizontally and laterally slidingly arranged on the workbench base 1. The first screw is horizontally and laterally arranged and rotatably connected to the workbench base 1. The first handle is connected to one end of the first screw. A screw sleeve adapted to the first screw is fixedly installed at the bottom of the first sliding seat 27. The first screw is inserted into the screw sleeve and is threadedly connected to the screw sleeve. It also includes a driven longitudinal feed system 26 for making the first mounting bracket body 11 approach / move away from the test piece bracket 12. The driven longitudinal feed system 26 includes a second handle and a second screw. The first mounting bracket body 11 is set on the first sliding seat 27 along the horizontal longitudinal sliding. The second screw is set along the horizontal longitudinal direction and is rotatably connected to the first sliding seat 27. A screw sleeve is fixedly installed at the bottom of the first mounting bracket body 11. The second screw is threadedly connected to the screw sleeve at the bottom of the first mounting bracket body 11. The second handle is rotatably connected to the first sliding seat 27. The second handle and the second screw can be connected through a bevel gear transmission.

[0029] The second torque sensor 31 and the second grating angle encoder 32 are arranged side by side on the second mounting bracket body 13, and the load bracket body 41 is arranged on the second mounting bracket body 13, and the load bracket body 41 is arranged on the load motor for connecting with the second torque sensor 31. The workbench base 1 is provided with a load lateral feed system 33 for aligning the second torque sensor 31 and the second grating angle encoder 32 alternately with the measured reducer 10, and the load lateral feed system 33 includes a second sliding seat 35, a third handle and a third screw rod, the second sliding seat 35 is arranged on the workbench base 1 in a horizontal and lateral sliding manner, the third screw rod is arranged in a horizontal and lateral direction and is rotatably connected to the workbench base 1, the third handle is connected to one end of the third screw rod, and the third screw rod is threadedly connected to the second sliding seat 35. It also includes a load longitudinal feed system 34 for making the second mounting bracket body 13 approach / move away from the test piece bracket 12. The load longitudinal feed system 34 includes a fourth handle and a fourth screw. The second mounting bracket body 13 is set on the second sliding seat 35 along the horizontal longitudinal sliding. The fourth screw is set along the horizontal longitudinal and is rotatably connected to the second sliding seat 35. The fourth screw is threadedly connected to the second mounting bracket body 13. The fourth handle is rotatably connected to the first sliding seat 27 and is transmission-connected to the fourth screw.

[0030] By flexibly adjusting the first mounting bracket and the second mounting bracket to slide horizontally on the workbench base 1, the first torque sensor 21, the first grating angle encoder 22, the second torque sensor 31 and the second grating angle encoder 32 can be flexibly aligned with the reducer 10 under test on the test piece bracket 12, and then the first mounting bracket and the second mounting bracket are driven to slide horizontally and longitudinally on the workbench base 1, and the reducer 10 under test can be selectively connected to the first torque sensor 21 / first grating angle encoder 22 and the second torque sensor 31 / second grating angle encoder 32 on both sides or selectively unloaded, so as to realize different types of performance test assembly of the reducer.

[0031] Different from the traditional method of coaxially connecting the grating angle encoder and the torque sensor, and performing transmission error or friction test and efficiency test under the common equipment, in the embodiment of the present application, when performing the transmission error test, the first grating angle encoder 22 and the second grating angle encoder 32 are simultaneously moved to align with the reducer 10 under test, and connected to the reducer 10 under test. Since the reducer 10 under test is a micro-precision reducer, the output torque at the output end is small, and the use of a single second grating angle encoder 32 can ensure that the friction torque at the output end is small, and reduce the accuracy change caused by the rigid deformation of the micro-reducer. In the embodiment of the present application, the second grating angle encoder 32 uses a real axis high-precision grating.

[0032] Further, the load motor includes a first load servo motor 42 and a second load servo motor 43 arranged side by side, and the first load servo motor 42 and the second load servo motor 43 have different powers. The second mounting bracket body 13 is provided with a transposition lateral feed system 44 for driving the first load servo motor 42 and the second load servo motor 43 to alternately align with the second torque sensor 31, and the transposition lateral feed system 44 includes a third sliding seat 46, a fifth handle and a fifth screw rod, the third sliding seat 46 is horizontally and laterally slidably arranged on the second mounting bracket body 13, the fifth screw rod is horizontally and laterally arranged and rotatably connected to the second mounting bracket body 13, the fifth handle is connected to one end of the fifth screw rod, and the fifth screw rod is threadedly connected to the third sliding seat 46. The third sliding seat 46 is provided with a transposition longitudinal feed system 45 for making the load support body 41 approach / move away from the second mounting support body 13. The transposition longitudinal feed system 45 includes a sixth handle and a sixth screw rod. The load support body 41 is arranged on the third sliding seat 46 along the horizontal longitudinal sliding direction. The sixth screw rod is arranged along the horizontal longitudinal direction and is rotatably connected to the third sliding seat 46. The sixth screw rod is threadedly connected to the sixth mounting support body. The sixth handle is rotatably connected to the third sliding seat 46 and is transmission connected to the sixth screw rod.

[0033] According to the different load capacities of the speed reducer 10 under test, when testing the load and other related items of the speed reducer 10 under test, load motors with different powers can be selected to connect the speed reducer 10 under test through the second torque sensor 31, thereby increasing its applicable speed reducer detection range. In the embodiment of the present application, the motor and the torque sensor, the torque sensor and the speed reducer 10 under test, and the grating angle sensor and the speed reducer 10 under test can be connected by keyways and key bars.

[0034] Furthermore, a manual locking mechanism 5 for limiting the sliding movement of the first sliding seat 27, the driving support body, the second sliding seat 35, the second support body, the third sliding seat 46 and the load support body 41 are all provided. Specifically, the manual locking mechanism 5 includes a locking bolt, a handle, a mounting block and a slider. The slider is slidably mounted on the relative sliding body along the sliding direction of the sliding body. The mounting block is fixedly mounted on the sliding body. The mounting block is vertically penetrated with a through hole. The slider is provided with a screw hole adapted to the locking bolt. The handle is fixed on the top of the locking bolt. The bolt passes through the through hole on the mounting block and is threadedly connected with the screw hole on the slider. By tightening the handle, the locking bolt presses down the mounting block and the slider has a tendency to move upward relative to the sliding body, thereby fixing the sliding body and the relative sliding body. After the first sliding seat 27, the driving support body, the second sliding seat 35, the second support body, the third sliding seat 46 and the load support body 41 are moved into place, they can be fixed and positioned to improve the stability of each structure on the test process device and ensure the accuracy of the test results.

[0035] Furthermore, a brake 6 and a third torque sensor 7 are connected in sequence between the second servo drive motor 24 and the first grating angle encoder 22 .

[0036] In the embodiments of the present application, the following performance tests may be performed:

[0037] In the no-load friction test, the first servo drive motor 23 is connected to the first torque sensor 21 and then connected to the reducer 10 under test. The load end is not connected to any structure. The reducer 10 under test is driven to rotate by the first servo drive motor 23 to test the no-load friction force of the reducer under test at different speeds.

[0038] In the starting friction test, the first servo drive motor 23 is connected to the first torque sensor 21 and then connected to the reducer 10 under test. The load end is not connected to any structure. The first servo drive motor 23 is started to gradually increase the force applied to the reducer 10 under test until the reducer 10 under test rotates under the force, which is considered to be the start of the reducer 10 under test. The maximum force applied to cause the reducer 10 under test to start is the start force of the reducer 10 under test.

[0039] In the efficiency test, the first servo drive motor 23 is connected to the first torque sensor 21, which is connected to the reducer 10 under test. The load end is connected to the second torque sensor 31 and a load motor. A suitable load motor is selected according to the output power of the reducer 10 under test. The efficiency of the reducer 10 under test is obtained by dividing the power at the output end of the reducer 10 under test by the power at the drive end and multiplying by 100%. The load of the load motor is gradually increased under the constant speed drive of the first servo drive motor 23, and the efficiency curve of the reducer 10 under test is drawn.

[0040] In the transmission error test, the second servo drive motor 24 is connected to the first grating angle encoder 22, connected to the reducer 10 under test, and the load end is connected to the second grating angle encoder 32. The numerical values ​​are obtained from the second servo drive motor 24 and the first grating angle encoder 22 at the driving end of the reducer 10 under test, and the theoretical parameters of the output end of the reducer 10 under test are obtained by calibrating the parameters of the reducer 10 under test, and the values ​​are subtracted from the values ​​obtained from the second grating angle encoder 32 to obtain the actual transmission error of the reducer 10 under test;

[0041] Repeated positioning test, using the second servo drive motor 24 connected to the first grating angle encoder 22, connected to the reducer 10 under test, the load end is connected to the second grating angle encoder 32, the drive end of the reducer 10 under test repeatedly rotates forward and reverse for the same number of circles, and the transmission error value at multiple points is recorded, and the repeated positioning parameters of the reducer 10 under test are calculated according to the national standard;

[0042] In the stiffness test, the second servo drive motor 24, the brake 6, the third torque sensor 7, the first grating angle encoder 22, the reducer 10 under test, the second grating angle encoder 32, and the load motor are connected. The driving end of the reducer 10 under test is locked by the brake 6. The load motor at the load end repeatedly rotates forward and reverse and gradually applies force to the rated parameter value of the reducer 10 under test. A closed curve is drawn with reference to the numerical values ​​of the first grating angle encoder 22 and the second grating angle encoder 32, and data such as the stiffness value is obtained.

[0043] It should be understood by those skilled in the art that, although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A micro-torque precision reducer performance test device, characterized in that: The invention comprises a workbench base (1), on which a first mounting bracket body (11), a test piece bracket (12), a second mounting bracket body (13) and a load bracket body (41) are arranged in sequence in the horizontal and longitudinal directions, and a test piece bracket (12) is detachably mounted with a test reducer (10); A first torque sensor (21) and a first grating angle encoder (22) are arranged side by side on the first mounting bracket body (11); an input end of the first torque sensor (21) and an input end of the first grating angle encoder (22) are respectively connected to a first servo drive motor (23) and a second servo drive motor (24); a driving transverse feed system (25) for alternately aligning the first torque sensor (21) and the first grating angle encoder (22) with the reducer (10) to be measured, and a driving longitudinal feed system (26) for moving the first mounting bracket body (11) closer to / away from the measured component bracket (12) are arranged on the workbench base (1); A second torque sensor (31) and a second grating angle encoder (32) are arranged side by side on the second mounting bracket body (13); a load bracket body (41) is arranged on the second mounting bracket body (13); a load motor for connecting to the second torque sensor (31) is arranged on the load bracket body (41); a load transverse feed system (33) for alternately aligning the second torque sensor (31) and the second grating angle encoder (32) with the reducer (10) to be measured, and a load longitudinal feed system (34) for moving the second mounting bracket body (13) closer to / away from the measured component bracket (12) are arranged on the workbench base (1).

2. The micro-torque precision reducer performance test device according to claim 1 is characterized in that: The driving transverse feed system (25) comprises a first sliding seat (27), a first handle and a first screw rod, wherein the first sliding seat (27) is horizontally and transversely slidably arranged on the workbench base (1), the first screw rod is horizontally and transversely arranged and rotatably connected to the workbench base (1), the first handle is connected to one end of the first screw rod, and the first screw rod is threadedly connected to the first sliding seat (27); The driving longitudinal feed system (26) comprises a second handle and a second screw rod, the first mounting bracket body (11) is slidably arranged on a first sliding seat (27) along a horizontal longitudinal direction, the second screw rod is arranged along a horizontal longitudinal direction and is rotatably connected to the first sliding seat (27), the second screw rod is threadedly connected to the first mounting bracket body (11), and the second handle is rotatably connected to the first sliding seat (27) and is transmission-connected to the second screw rod.

3. The micro-torque precision reducer performance testing device according to claim 2 is characterized in that: The load lateral feed system (33) comprises a second sliding seat (35), a third handle and a third screw rod, wherein the second sliding seat (35) is horizontally and laterally slidably arranged on the workbench base (1), the third screw rod is horizontally and laterally arranged and rotatably connected to the workbench base (1), the third handle is connected to one end of the third screw rod, and the third screw rod is threadedly connected to the second sliding seat (35); The load longitudinal feed system (34) comprises a fourth handle and a fourth screw, the second mounting bracket body (13) is slidably arranged on the second sliding seat (35) along the horizontal longitudinal direction, the fourth screw is arranged along the horizontal longitudinal direction and is rotatably connected to the second sliding seat (35), the fourth screw is threadedly connected to the second mounting bracket body (13), and the fourth handle is rotatably connected to the first sliding seat (27) and is transmission-connected to the fourth screw.

4. The micro-torque precision reducer performance testing device according to claim 3 is characterized in that: The load motor comprises a first load servo motor (42) and a second load servo motor (43) arranged side by side, the first load servo motor (42) and the second load servo motor (43) have different powers, and the second mounting bracket body (13) is provided with a transposition lateral feed system (44) for driving the first load servo motor (42) and the second load servo motor (43) to alternately align with the second torque sensor (31), and a transposition longitudinal feed system (45) for making the load bracket body (41) approach / move away from the second mounting bracket body (13); The transposition lateral feed system (44) comprises a third sliding seat (46), a fifth handle and a fifth screw rod, wherein the third sliding seat (46) is horizontally and laterally slidably arranged on the second mounting bracket body (13), the fifth screw rod is horizontally and laterally arranged and rotatably connected to the second mounting bracket body (13), the fifth handle is connected to one end of the fifth screw rod, and the fifth screw rod is threadedly connected to the third sliding seat (46); The transposition longitudinal feed system (45) comprises a sixth handle and a sixth screw rod, the load support body (41) is arranged on the third sliding seat (46) along the horizontal longitudinal sliding, the sixth screw rod is arranged along the horizontal longitudinal direction and is rotatably connected to the third sliding seat (46), the sixth screw rod is threadedly connected to the sixth mounting support body, and the sixth handle is rotatably connected to the third sliding seat (46) and is transmission-connected to the sixth screw rod.

5. The micro-torque precision reducer performance testing device according to claim 4 is characterized in that: The first sliding seat (27), the driving bracket body, the second sliding seat (35), the second bracket body, the third sliding seat (46) and the load bracket body (41) are all provided with a manual locking mechanism (5) for limiting their own sliding.

6. The micro-torque precision reducer performance test device according to any one of claims 1 to 5, characterized in that: A brake (6) and a third torque sensor (7) are connected in sequence between the second servo drive motor (24) and the first grating angle encoder (22).

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