A dual differential capacitive torque sensor

Abstract

The present invention discloses a double differential capacitive torque sensor, which is composed of a sensor outer ring, a plurality of deformation beams, a sensor inner ring, a capacitive moving electrode part, an overload protection part, a substrate, a capacitive static electrode part, etc. The capacitive moving electrode part and the capacitive static electrode part form 4 capacitors, wherein the first capacitor and the third capacitor are symmetrically distributed about the x-axis, constituting a differential structure one; the second capacitor and the fourth capacitor are symmetrically distributed about the y-axis, constituting a differential structure two; the differential structure one and the differential structure two are orthogonally distributed, constituting a double differential structure. Through the double differential structure, the sensitivity and reliability of the torque sensor can be effectively improved, the linear error can be reduced, and the interference caused by the lateral force can be offset. Applying the torque feedback information of the sensor to robot control can achieve precise torque control of the robot and improve the operation efficiency of the robot.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, relates to force sensors, and particularly relates to a double differential capacitive torque sensor. Background Art

[0002] As a structural sensor, torque sensors have been widely used in many fields that require torque measurement. According to the way of generating torque signals, torque sensors can be divided into optical, optoelectronic, capacitive, electromagnetic, and strain types, etc. Its principle is to convert the corresponding electrical signal by using the change of structural parameters. Currently, the more mature torque sensors on the market are mainly electromagnetic and strain types. The essence of the output signal of the electromagnetic torque sensor is two angular displacement signals with a phase difference. The torque information is obtained by combining and processing the signals; this sensor is a non-contact sensor without wear, but due to its large volume, it is not suitable for measuring the torque of robot joints. The strain torque sensor usually has a complex structure, difficult torque decoupling, and requires additional signal amplification circuits, A / D converters, etc.

[0003] The capacitive torque sensor is made based on the relevant laws of the electrostatic field as its theoretical basis, and has the advantages of good temperature stability, simple structure, good dynamic response, and can achieve non-contact measurement; therefore, the capacitive torque sensor has been widely used in physical measurements such as thickness, displacement, pressure, speed, and concentration in recent years. However, currently in the application of robot joints, due to the low sensitivity, poor anti-interference ability, and being easily affected by lateral forces and overload torques of the capacitive torque sensor, it is difficult to achieve precise torque control when the robot hand grasps an object or the robot end needs to complete a specific action, thus reducing the accuracy of the robot control system. Summary of the Invention

[0004] The purpose of the present invention is to propose a double differential capacitive torque sensor in view of the deficiencies of the current capacitive torque sensors; by adopting a double differential structure, the sensitivity and linearity of the torque sensor are improved, and at the same time, the influence caused by interference such as lateral forces is eliminated.

[0005] To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0006] A double differential capacitive torque sensor includes a sensor outer ring 1, several deformation beams 2, a sensor inner ring 3, a capacitive moving electrode part 4, an overload protection part 5, a substrate 6, a capacitive static electrode part 7, etc. A number of circular bosses 9 and U-shaped bosses 10 are evenly distributed on the sensor outer ring 1, and threaded holes are provided on the bosses. The threaded holes on the circular bosses 9 are used to connect the substrate 6, and the substrate 6 can be fixed to the sensor outer ring 1 through the annular groove 11 on the substrate 6; the threaded holes on the U-shaped bosses 10 are used for the connection between the sensor and the load. A number of threaded holes 8 are evenly distributed on the sensor inner ring 3 for the connection between the sensor and the reducer; the deformation beam 2 is of a trapezoidal structure, and its two ends are respectively connected to the sensor outer ring 1 and the sensor inner ring 3, playing a role in transmitting torque. A rectangular groove 12 is also provided on the substrate 6, and the capacitive static electrode part 7, the sensing elements used by the sensor, and the detection circuit are distributed. The rectangular groove 12 is used to place the capacitive moving electrode part 4.

[0007] The capacitive moving electrode part 4 includes a first moving electrode 4-1, a second moving electrode 4-2, a third moving electrode 4-3, and a fourth moving electrode 4-4; the capacitive static electrode part 7 includes a first static electrode 7-1, a second static electrode 7-2, a third static electrode 7-3, and a fourth static electrode 7-4; the first moving electrode 4-1 is perpendicular to the first static electrode 7-1, and there is a certain gap between the two electrodes, forming a first capacitor 13-1 with capacitive edge effect; the second moving electrode 4-2 is perpendicular to the second static electrode 7-2, and there is a certain gap between the two electrodes, forming a second capacitor 13-2 with capacitive edge effect; the third moving electrode 4-3 is perpendicular to the third static electrode 7-3, and there is a certain gap between the two electrodes, forming a third capacitor 13-3 with capacitive edge effect; the fourth moving electrode 4-4 is perpendicular to the fourth static electrode 7-4, and there is a certain gap between the two electrodes, forming a fourth capacitor 13-4 with capacitive edge effect; the first capacitor 13-1 and the third capacitor 13-3 are symmetrically distributed about the x-axis, forming a differential structure one; the second capacitor 13-2 and the fourth capacitor 13-4 are symmetrically distributed about the y-axis, forming a differential structure two; the differential structure one and the differential structure two are orthogonally distributed, forming a double differential structure. When the sensor works, if the electrode pitch of the first capacitor 13-1 decreases (increases) by Δh, the measured capacitance is C1, and the capacitance increase (decrease) value is ΔC1, then the electrode pitch of the third capacitor 13-3 will increase (decrease) by Δh, the measured capacitance is C3, and the capacitance decrease (increase) value is ΔC3. Taking the difference (C1 - C3) as the input signal terminal 1 for torque detection, the capacitance change is (ΔC1 + ΔC3); similarly, if the electrode pitch of the second capacitor 13-2 decreases (increases) by Δh, the measured capacitance is C2, and the capacitance increase (decrease) value is ΔC2, then the electrode pitch of the fourth capacitor 13-4 will increase (decrease) by Δh, the measured capacitance is C4, and the capacitance decrease (increase) value is ΔC4. Taking the difference (C2 - C4) as the input signal terminal 2 for torque detection, the capacitance change is (ΔC2 + ΔC4); it can be seen that the capacitance change increases, thus improving the sensitivity of the sensor. By converting the capacitance change amount (ΔC1 + ΔC3) into torque T1, and the capacitance change amount (ΔC2 + ΔC4) into torque T2, the lateral forces carried by T1 and T2 can cancel each other out, and the actual output torque is: T = (T1 + T2) / 2. Therefore, adopting the double differential structure to obtain the torque output of the sensor can not only improve the sensitivity and reliability of the sensor, reduce the linear error; at the same time, it can also effectively suppress the influence of the lateral force on the output signal, thereby improving the control accuracy of the robot's movement.

[0008] The overload protection part 5 includes an overload protection beam 14 and an overload protection block 15; the overload protection beam 14 is a cantilever beam fixedly connected to the outer edge of the inner ring 3 of the sensor, and there are bumps and countersunk screw holes 16 on the beam. The bumps are used as the second moving electrode 4-2 and the fourth moving electrode 4-4 of the capacitor; the overload protection block 15 is an L-shaped structure, which is fixed to both sides of the end of the overload protection beam 14 through the countersunk screw holes 16 by bolts. At the same time, there is a certain gap between the overload protection block 15 and the outer ring 1 of the sensor, and this gap is slightly smaller than the gap between the two electrodes of the capacitor. When overload occurs, the overload protection block 18 first contacts the outer ring 1 of the sensor, thereby preventing the contact between the moving electrode part 4 and the static electrode part 7 of the capacitor, playing a protective role. In the overload protection part 5, the moving electrode of the capacitor is arranged on the overload protection beam 14, which can not only save the internal space of the sensor, but also play a dual role of overload protection and acting as the moving electrode of the capacitor.

[0009] The features and beneficial effects of the present invention are as follows:

[0010] The present invention adopts a double differential non-contact electrode structure, in which the electrodes are orthogonally distributed. The capacitance value of the first capacitor is subtracted from the capacitance value of the third capacitor, and the capacitance value of the second capacitor is subtracted from the capacitance value of the fourth capacitor. Two sets of torque values are obtained by converting the two sets of capacitance differences, and then the average value of the two sets of torque values is taken to obtain the torque output value of the sensor. Through the double differential structure, the sensitivity and reliability of the torque sensor can be effectively improved, the linear error can be reduced, and the interference caused by the lateral force can be offset. The capacitance torque sensor of the present invention has a simple structure, is easy to assemble, does not require additional converters and sensors, reduces the cost and can achieve good results at the same time. Brief Description of the Drawings

[0011] Figure 1 is the exploded perspective view of the present invention.

[0012] Figure 2 is the schematic perspective assembly view of the present invention.

[0013] Figure 3 is Figure 2 the view from direction A of

[0014] Figure 4 is the partial enlarged view of the overload protection part of the present invention.

[0015] In the attached drawings: 1. Outer ring of the sensor; 2. Deformation beam; 3. Inner ring of the sensor; 4. Capacitive moving electrode part; 4-1. First moving electrode; 4-2. Second moving electrode; 4-3. Third moving electrode; 4-4. Fourth moving electrode; 5. Overload protection part; 6. Substrate; 7. Capacitive static electrode part; 7-1. First static electrode; 7-2. Second static electrode; 7-3. Third static electrode; 7-4. Fourth static electrode; 8. Threaded hole; 9. Circular boss; 10. U-shaped boss; 11. Ring-shaped groove; 12. Rectangular groove; 13. Capacitor; 13-1. First capacitor; 13-2. Second capacitor; 13-3. Third capacitor; 13-4. Fourth capacitor; 14. Overload protection beam; 15. Overload protection block; 16. Countersunk threaded hole. Detailed implementation manner

[0016] In order to better understand the present invention, exemplary embodiments of the present invention will be described below in conjunction with the attached drawings.

[0017] As shown Figures 1 to 4 in the figure, a dual differential capacitive torque sensor of the present invention includes an outer ring 1 of the sensor, several deformation beams 2, an inner ring 3 of the sensor, a capacitive moving electrode part 4, an overload protection part 5, a substrate 6, a capacitive static electrode part 7, etc. Several circular bosses 9 and U-shaped bosses 10 are evenly distributed on the outer ring 1 of the sensor, and threaded holes are provided on the bosses. The threaded hole on the circular boss 9 is used to connect the substrate 6, and the substrate 6 can be fixed to the outer ring 1 of the sensor through the ring-shaped groove 11 on the substrate 6; the threaded hole on the U-shaped boss 10 is used for the connection between the sensor and the load. Several threaded holes 8 are evenly distributed on the inner ring 3 of the sensor, which are used for the connection between the sensor and the reducer. The deformation beam 2 is of a trapezoidal structure, and its two ends are respectively connected to the outer ring 1 and the inner ring 3 of the sensor, playing a role in transmitting torque. The number of deformation beams in the figure is 4, but in the actual production process, the number of deformation beams can be adjusted according to the magnitude of the torque. A rectangular groove 12 is also provided on the substrate 6, and the capacitive static electrode part 7 and the sensing elements and detection circuits used by the sensor are distributed at the same time. The rectangular groove 12 is used to place the capacitive moving electrode part 4.

[0018] The capacitive moving electrode part 4 includes a first moving electrode 4-1, a second moving electrode 4-2, a third moving electrode 4-3, and a fourth moving electrode 4-4; the capacitive static electrode part 7 includes a first static electrode 7-1, a second static electrode 7-2, a third static electrode 7-3, and a fourth static electrode 7-4; the first moving electrode 4-1 is perpendicular to the first static electrode 7-1, and there is a certain gap between the two electrodes, forming a first capacitor 13-1 with capacitive edge effect; the second moving electrode 4-2 is perpendicular to the second static electrode 7-2, and there is a certain gap between the two electrodes, forming a second capacitor 13-2 with capacitive edge effect; the third moving electrode 4-3 is perpendicular to the third static electrode 7-3, and there is a certain gap between the two electrodes, forming a third capacitor 13-3 with capacitive edge effect; the fourth moving electrode 4-4 is perpendicular to the fourth static electrode 7-4, and there is a certain gap between the two electrodes, forming a fourth capacitor 13-4 with capacitive edge effect; wherein, the first capacitor 13-1 and the third capacitor 13-3 are symmetrically distributed about the x-axis, forming a differential structure one, that is, when the sensor is subjected to a moment, the capacitance of the first capacitor 13-1 increases (decreases), and the capacitance of the third capacitor 13-3 decreases (increases); the second capacitor 13-2 and the fourth capacitor 13-4 are symmetrically distributed about the y-axis, forming a differential structure two, that is, when the sensor is subjected to a moment, the capacitance of the second capacitor 13-2 increases (decreases), and the capacitance of the fourth capacitor 13-4 decreases (increases); the differential structure one and the differential structure two are orthogonally distributed, forming a double differential structure.

[0019] Its working principle is as follows: when a moment is applied, the trapezoidal beam deformable body deforms, and a small angular displacement occurs in the inner circle of the sensor. The electrode pole pitch of the first capacitor 13-1 decreases (increases) by Δh, its capacitance is C1, and the capacitance increase (decrease) value is ΔC1. Then the electrode pole pitch of the third capacitor 13-3 will increase (decrease) by Δh, its capacitance is C3, and the capacitance decrease (increase) value is ΔC3. Taking the difference of (C1 - C3) as the input signal terminal 1 for moment detection, the capacitance change amount is (ΔC1 + ΔC3); similarly, the electrode pole pitch of the second capacitor 13-2 decreases (increases) by Δh, its capacitance is C2, and the capacitance increase (decrease) value is ΔC2. Then the electrode pole pitch of the fourth capacitor 13-4 will increase (decrease) by Δh, its capacitance is C4, and the capacitance decrease (increase) value is ΔC4. Taking the difference of (C2 - C4) as the input signal terminal 2 for moment detection, the capacitance change amount is (ΔC2 + ΔC4). Analyzing its electric field distribution by electromagnetic theory, the approximate formula for the sensitivity of capacitance change caused by such capacitance distance can be obtained as follows:

[0020]

[0021] Among them, K is proportional to the change amount of capacitance and inversely proportional to the change distance.

[0022] As can be seen from the above analysis, for the double differential capacitive torque sensor, the capacitance change amounts are (ΔC1 + ΔC3) and (ΔC2 + ΔC4), while for the non-double differential capacitive torque sensor, the capacitance change amount is ΔC1 or ΔC2 or ΔC3 or ΔC4; therefore, the double differential structure increases the capacitance change amount, thereby improving the sensitivity and linearity of the sensor. At the same time, the capacitance change amount (ΔC1 + ΔC3) is converted into torque T1, and the capacitance change amount (ΔC2 + ΔC4) is converted into torque T2. The lateral forces carried by T1 and T2 can cancel each other out, and the actual output torque is: T = (T1 + T2) / 2.

[0023] The overload protection part 5 includes an overload protection beam 14 and an overload protection block 15; the overload protection beam 14 is a cantilever beam fixedly connected to the outer edge of the inner ring 3 of the sensor. There are bumps and countersunk screw holes 16 on the beam. The bumps are used as the second moving electrode 4-2 and the fourth moving electrode 4-4 of the capacitor; the overload protection block 15 is of an L-shaped structure. It is fixed to both sides of the end of the overload protection beam 14 by bolts through the countersunk screw holes 16. At the same time, there is a certain gap between the overload protection block 15 and the outer ring 1 of the sensor, and this gap is slightly smaller than the gap between the moving electrode and the static electrode of the capacitor. When an overload occurs, the overload protection block 15 first contacts the outer ring 1 of the sensor, thus preventing the contact between the moving electrode part 4 and the static electrode part 7 of the capacitor and playing a protective role. In the overload protection part 5, the second moving electrode and the fourth moving electrode are cleverly arranged on the overload protection beam 14, which not only does not require electrodes to be arranged in other positions, saving the internal space of the sensor, but also can play a dual role of overload protection and acting as a moving electrode of the capacitor.

[0024] The above is only the preferred embodiment of the present invention, and the present invention is not limited to this example. In this embodiment, two pairs of differential capacitors are used, and even pairs of differential capacitors containing more than two pairs are also within the protection scope of the present invention. It should be pointed out that within the scope of this technical field, all equivalent technical changes studied using the principle of the present invention are included in the patent scope of the present invention.

Claims

1. A double differential capacitive torque sensor, characterized in that: It at least includes a sensor outer ring (1), a plurality of deformation beams (2), a sensor inner ring (3), a capacitive moving electrode part (4), an overload protection part (5), a substrate (6) and a capacitive static electrode part (7); the capacitive moving electrode part (4) at least includes a first moving electrode (4-1), a second moving electrode (4-2), a third moving electrode (4-3), and a fourth moving electrode (4-4); the capacitive static electrode part (7) at least includes a first static electrode (7-1), a second static electrode (7-2), a third static electrode (7-3), and a fourth static electrode (7-4); the capacitive moving electrode part (4) and the capacitive static electrode part (7) form a double differential vertical electrode type capacitor (13); the double differential vertical electrode type capacitor (13) means that: the first moving electrode (4-1) is perpendicular to the first static electrode (7-1), and there is a certain gap between the two electrodes, forming a first capacitor (13-1) with capacitive edge effect; the second moving electrode (4-2) is perpendicular to the second static electrode (7-2), and there is a certain gap between the two electrodes, forming a second capacitor (13-2) with capacitive edge effect; the third moving electrode (4-3) is perpendicular to the third static electrode (7-3), and there is a certain gap between the two electrodes, forming a third capacitor (13-3) with capacitive edge effect; the fourth moving electrode (4-4) is perpendicular to the fourth static electrode (7-4), and there is a certain gap between the two electrodes, forming a fourth capacitor (13-4) with capacitive edge effect; the first capacitor (13-1) and the third capacitor (13-3) are symmetrically distributed about the x-axis, forming a first differential structure; the second capacitor (13-2) and the fourth capacitor (13-4) are symmetrically distributed about the y-axis, forming a second differential structure; the first differential structure and the second differential structure are orthogonally distributed, forming a double differential structure; the capacitance value of the first capacitor (13-1) is subtracted from the capacitance value of the third capacitor (13-3), the capacitance value of the second capacitor (13-2) is subtracted from the capacitance value of the fourth capacitor (13-4), two groups of torque values are obtained by converting the two groups of capacitance differences, and then the average value of the two groups of torque values is taken to obtain the torque output value of the sensor, which can effectively improve the sensitivity and reliability of the torque sensor, reduce the linear error, and cancel the interference caused by the lateral force; The substrate (6) is provided with an annular groove (11) and a rectangular groove (12), and the capacitive static electrode part (7) and the induction elements and detection circuits used by the sensor are distributed at the same time. The annular groove (11) is used to fix the substrate (6) on the sensor outer ring (1), and the rectangular groove (12) is used to place the capacitive moving electrode part (4).

2. The dual differential capacitive torque sensor according to claim 1, characterized in that: The differential structure one means that when the electrode pitch of the first capacitor (13-1) changes by Δh and its capacitance is C1, the electrode pitch of the third capacitor (13-3) changes by -Δh and its capacitance is C3, and the difference of (C1 - C3) is used as the input signal terminal 1 for torque detection; the differential structure two means that when the electrode pitch of the second capacitor (13-2) changes by Δh and its capacitance is C2, the electrode pitch of the fourth capacitor (13-4) changes by -Δh and its capacitance is C4, and the difference of (C2 - C4) is used as the input signal terminal 2 for torque detection.

3. The dual differential capacitive torque sensor according to claim 1, characterized in that: The overload protection part (5) at least includes an overload protection beam (14) and an overload protection block (15); the overload protection beam (14) is a cantilever beam fixedly connected to the outer edge of the inner ring (3) of the sensor, and there are bumps and threaded holes (16) on the beam, and the bumps are used as the second movable electrode (4-2) and the fourth movable electrode (4-4) of the capacitor; the overload protection block (15) is of an L-shaped structure, and it is fixed to both sides of the end of the overload protection beam (14) through the threaded holes (16), and there is a certain gap between the overload protection block (15) and the outer ring (1) of the sensor; the overload protection part (5) plays a dual role of overload protection and acting as a movable electrode of the capacitor.

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