JP7546438B2 - Correction system, correction device, and correction method - Google Patents

Description

This invention relates to a correction system, a correction device, and a correction method for correcting the position error of a strain wave gear reducer.

When the input side (wave generator) of a wave gear reducer is fixed and torque is applied to the output side (flexspline), a torsion proportional to the torque is generated on the output side. As shown in FIG. 5, when this torque is applied up to the rated value and then returned to zero, the torsion does not become completely zero but remains slightly due to the influence of internal friction and the like. This is called hysteresis loss. The torsion angle is the cause of position errors in wave gear reducers. The torsional stiffness (spring constant) represents the relationship between the torsion angle and the torque, and is divided into three categories according to the torque range. Note that FIG. 5 shows the case where torque is applied while changing the value in the order of 0, +T ₀ , 0, -T ₀ , 0, +T _0, and shows that the torsion angle changes in the order of 0, A, B, A', B', A. Also, in FIG. 5, HL represents hysteresis loss.

Conventionally, the following countermeasures have been taken to address position errors caused by the torsion angle (see, for example, Patent Documents 1 and 2). For example, the torsion angle caused by torque is measured in advance, or a characteristic (hysteresis characteristic) indicating the torsion angle is obtained from the manufacturer of the strain wave gear reducer, and the position error is corrected (first countermeasure). For example, an angular rotation position detector is attached to the output side of the strain wave gear reducer, and the position is directly detected by this angular rotation position detector, and the position error is corrected (second countermeasure). For example, the output torque is estimated from the motor current value of the actuator that drives the strain wave gear reducer, and the position error is corrected (third countermeasure).

Japanese Patent Application Publication No. 10-164879 JP 2018-36097 A

In the first measure, for example, a hysteresis characteristic as shown in FIG. 6 can be obtained. The hysteresis characteristic shown in FIG. 6 shows the same content as that shown in FIG. 5. In FIG. 6, reference numeral 601 indicates the hysteresis characteristic. Reference numeral 602 indicates the spring constant (theoretical line). Furthermore, T ₀ indicates the rated torque. If the torque (torque at the time of stopping) applied to the output side of the strain wave gear reducer is known from this hysteresis characteristic, the torsion angle generated on the output side can also be grasped. However, this hysteresis characteristic shows the characteristic when the torque is applied to the output side of the strain wave gear reducer up to the rated value. And, if the torque is not applied to the output side of the strain wave gear reducer up to the rated value, the hysteresis characteristic changes. Therefore, in the first measure, there are cases where the amount of position error due to the torsion angle cannot be accurately estimated.

Furthermore, the second measure requires an expensive high-resolution angle/rotation position detector, and it may be difficult to provide the angle/rotation position detector due to reasons such as the installation location and calibration.
Furthermore, in the third measure, the motor current value is easily affected by electrical noise, Joule heat, and the temperature characteristics of the motor torque constant, and the estimation accuracy is low.

This invention was made to solve the above problems, and aims to provide a correction system that can correct the position error of a strain wave gear reducer more easily and with higher accuracy than conventional configurations, even when torque is not applied to the output side of the strain wave gear reducer up to the rated value.

The correction system according to the present invention is characterized by comprising a rotational position detector that detects the rotational position of an actuator that drives a strain wave gear reducer, a sensor that detects the torque applied to the output side of the strain wave gear reducer, a calculation unit that calculates the hysteresis characteristics within the fluctuation range of the torque based on the hysteresis characteristics within the rated torque range for the strain wave gear reducer and the torque detected by the sensor, and calculates the torsion angle generated on the output side of the strain wave gear reducer, and a control unit that controls the actuator based on the rotational position detected by the rotational position detector and the torsion angle calculated by the calculation unit.

According to this invention, because of the above configuration, even if the rated torque is not applied to the output side of the strain wave gear reducer, it is possible to correct the position error of the strain wave gear reducer more easily and with higher accuracy than with conventional configurations.

FIG. 1 is a diagram illustrating a configuration example of a correction system according to a first embodiment. FIG. 2 is a diagram showing a configuration example of a strain wave gear reducer. 5 is a flowchart showing an example of the operation of the correction device according to the first embodiment. 4A and 4B are diagrams for explaining an example of the operation of the calculation unit in the first embodiment, where FIG. 4A is a diagram for explaining a conventional method and FIG. 4B is a diagram for explaining the method of the first embodiment. FIG. 1 is a diagram showing an example of a torsion angle generated by a torque applied to the output side of a strain wave gear reducer. FIG. 11 is a diagram showing an example of hysteresis characteristics in the range of rated torque for a strain wave gear reducer.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
Embodiment 1.
FIG. 1 is a diagram showing an example of the configuration of a correction system 1 according to the first embodiment.
The correction system 1 corrects the position error of the strain wave gear reducer 2. As shown in Fig. 1, the correction system 1 includes a rotational position detector 11, a sensor 12, a storage unit 13, a calculation unit 14, and a control unit 15. The calculation unit 14 and the control unit 15 constitute a correction device. This correction device is realized by a processing circuit such as a system LSI (Large Scale Integration), or a CPU (Central Processing Unit) that executes a program stored in a memory or the like. In addition to the correction system 1, Fig. 1 also shows a strain wave gear reducer 2 and an actuator 3.

The strain wave gear reducer 2 is a reducer that utilizes the differential between an ellipse and a perfect circle. As shown in FIG. 2, the strain wave gear reducer 2 has a circular spline 21, a wave generator 22, and a flexspline 23.

The circular spline 21 is a ring-shaped rigid part. The circular spline 21 has teeth on its inner circumference, and has two more teeth than the flexspline 23. The circular spline 21 is usually fixed to the casing.

The wave generator 22 is a component that combines a thin-walled ball bearing with the outer periphery of an elliptical cam. In a ball bearing, the inner ring is fixed to the cam, but the outer ring is elastically deformed via the balls. The wave generator 22 is usually attached to the input shaft (actuator 3).

The flexspline 23 is a thin-walled, cup-shaped elastic metal part. The flexspline 23 has teeth cut into the outer periphery of its opening. The bottom of the flexspline 23 is called the diaphragm, and is usually attached to the output shaft (e.g., a robot arm).

The flexspline 23 is bent into an elliptical shape by the wave generator 22, and the teeth of the circular spline 21 mesh with those of the major axis, while the teeth are completely separated from each other on the minor axis.

When the wave generator 22 is rotated clockwise with the circular spline 21 fixed, the flexspline 23 elastically deforms, and the meshing position of the teeth with the circular spline 21 moves sequentially. When the wave generator 22 rotates once clockwise, the flexspline 23 moves counterclockwise by an amount corresponding to the difference in the number of teeth (two teeth).
The same applies when the wave generator 22 is rotated counterclockwise with the circular spline 21 fixed, and the flexspline 23 elastically deforms, and the meshing position of the teeth with the circular spline 21 moves sequentially. When the wave generator 22 makes one rotation counterclockwise, the flexspline 23 moves clockwise by an amount corresponding to the difference in the number of teeth (two teeth).

The actuator 3 drives the strain wave gear reducer 2 (wave generator 22). This actuator 3 drives in response to commands from a controller (not shown).

The rotational position detector 11 detects the rotational position of the actuator 3. An encoder, for example, can be used as the rotational position detector 11.

The sensor 12 detects the torque applied to the output side (flexspline 23) of the strain wave gear reducer 2. For example, a torque sensor can be used as the sensor 12.

The memory unit 13 stores various information handled by the correction system 1. This memory unit 13 stores information indicating the hysteresis characteristics within the range of the rated torque for the strain wave gear reducer 2. The memory unit 13 is configured with a HDD (Hard Disk Drive), a DVD (Digital Versatile Disc), memory, etc.

Information indicating the hysteresis characteristics can be obtained, for example, from the manufacturer of the strain wave gear reducer 2. Information indicating the hysteresis characteristics can also be obtained in advance, for example, by applying torque of varying values to the output side of the strain wave gear reducer 2 and measuring the torsion angle at that time. Note that even for the same torque value, the torsion angle changes depending on the direction in which the torque increases or decreases (see Figures 5 and 6, etc.). For this reason, advance measurements are performed taking into account the direction in which the torque increases or decreases. In addition, when the strain wave gear reducer 2 is attached to a robot arm, information indicating the hysteresis characteristics can also be obtained by measuring the deviation of each axis of the robot arm from the position of the tip of the robot arm and performing comparative learning with the torque.

Note that FIG. 1 illustrates a case where the memory unit 13 is provided inside the correction system 1. However, this is not limited to the above, and the memory unit 13 may be provided outside the correction system 1.

The calculation unit 14 calculates the hysteresis characteristics within the fluctuation range of the torque based on the hysteresis characteristics within the rated torque range for the strain wave gear reducer 2 and the torque detected by the sensor 12, and calculates the torsion angle generated on the output side of the strain wave gear reducer 2. Note that the calculation unit 14 reads out the hysteresis characteristics within the rated torque range for the strain wave gear reducer 2 from the memory unit 13.

At this time, the calculation unit 14 first calculates a hysteresis characteristic (hysteresis characteristic in the torque fluctuation range) similar to the hysteresis characteristic in the rated torque range for the strain wave gear reducer 2 from the ratio between the torque fluctuation range detected by the sensor 12 and the rated torque range. More specifically, the calculation unit 14 compares the torque fluctuation range with the rated torque range, and calculates the hysteresis characteristic in the torque fluctuation range without changing the spring constant (slope of the curve) of the strain wave gear reducer 2. Then, the calculation unit 14 calculates the torsion angle generated on the output side of the strain wave gear reducer 2 from the hysteresis characteristic in the torque fluctuation range and the torque (stop torque) detected by the sensor 12. The torsion angle obtained at this time is the torsion angle when the torque increase/decrease direction is the increase direction, and the torsion angle when the torque increase/decrease direction is the decrease direction. Therefore, the calculation unit 14 calculates one of the two torsion angles as the torsion angle based on the direction of increase or decrease in the torque detected by the sensor 12. The torsion angle calculated by the calculation unit 14 corresponds to the position error of the strain wave gear reducer 2.

The control unit 15 controls the actuator 3 based on the rotational position detected by the rotational position detector 11 and the torsion angle calculated by the calculation unit 14. At this time, the control unit 15 controls the actuator 3 after taking into account the position error due to the torsion angle to the rotational position. This control unit 15 corrects the position error of the strain wave gear reducer 2.

Next, an example of the operation of the correction device according to the first embodiment shown in FIG. 1 will be described with reference to FIG. 3. The memory unit 13 stores information indicating the hysteresis characteristics within the range of the rated torque for the strain wave gear reducer 2 as shown in FIG. 6.

The rotational position detector 11 detects the rotational position of the actuator 3. The sensor 12 detects the torque applied to the output side (flexspline 23) of the strain wave gear reducer 2. The detection of the rotational position by the rotational position detector 11 and the detection of the torque by the sensor 12 are performed continuously.

In an example of the operation of the correction device according to the first embodiment shown in FIG. 1, as shown in FIG. 3, the calculation unit 14 first calculates a hysteresis characteristic (the hysteresis characteristic in the torque fluctuation range) similar to the hysteresis characteristic in the rated torque range for the strain wave gear reducer 2 from the ratio between the torque fluctuation range detected by the sensor 12 and the rated torque range (step ST301). More specifically, the calculation unit 14 compares the torque fluctuation range with the rated torque range, and calculates the hysteresis characteristic in the torque fluctuation range without changing the spring constant (slope of the curve) of the strain wave gear reducer 2. The calculation unit 14 reads out the hysteresis characteristic in the rated torque range for the strain wave gear reducer 2 from the memory unit 13.

Then, the calculation unit 14 calculates the torsion angle generated on the output side of the strain wave gear reducer 2 from the hysteresis characteristic in the torque fluctuation range and the torque (stop torque) detected by the sensor 12 (step ST302). The torsion angles obtained at this time are two torsion angles: one when the torque increase/decrease direction is an increase direction, and the other when the torque increase/decrease direction is a decrease direction. Therefore, the calculation unit 14 calculates one of the two torsion angles as the torsion angle based on the torque increase/decrease direction detected by the sensor 12. The torsion angle calculated by the calculation unit 14 corresponds to the position error of the strain wave gear reducer 2.

Here, in the past, as shown in FIG. 4A for example, if the torque (torque at rest) applied to the output side of the strain wave gear reducer 2 is known from the hysteresis characteristics in the range of the rated torque for the strain wave gear reducer 2, it is possible to calculate the theoretical torsion angle (theoretical torsion angle) generated on the output side, and this can be regarded as a position error. The theoretical torsion angle can be calculated by torque at rest/spring constant. The spring constant is obtained from the hysteresis characteristics in the range of the rated torque. However, this theoretical torsion angle is calculated from the hysteresis characteristics in the range of the rated torque, and if the torque applied to the output side of the strain wave gear reducer 2 is not up to the rated value, an error will occur in the actual torsion angle.
4A and 4B, reference numeral 401 indicates the hysteresis characteristic in the range of the rated torque. Reference numeral 402 indicates the spring constant (theoretical line). Furthermore, _T0 indicates the rated torque, _T1 indicates the torque at the time of stopping, and _φ1 indicates the theoretical torsion angle. Furthermore, HL indicates the hysteresis loss.

In contrast, in the calculation unit 14 in embodiment 1, as shown in FIG. 4B, a hysteresis characteristic similar to the hysteresis characteristic in the rated torque range is calculated based on the ratio between the fluctuation range of the torque applied to the output side of the strain wave gear reducer 2 and the rated torque range, and the torsion angle is calculated from this hysteresis characteristic.

At this time, the calculation unit 14 calculates the similar hysteresis characteristic without changing the spring constant (slope of the curve) of the strain wave gear reducer 2. In other words, the hysteresis characteristic in an arbitrary torque fluctuation range is similar to the hysteresis characteristic in the rated torque range because the spring characteristic of the strain wave gear reducer 2 is constant with respect to the hysteresis characteristic in the rated torque range and due to the relationship between the arbitrary torque fluctuation range and the rated torque range.
4B, even if the torque has the same value, the torsion angle changes depending on the direction of increase or decrease of the torque, and two torsion angles (a first torsion angle and a second torsion angle) exist. Therefore, the calculation unit 14 calculates one of the two torsion angles as the torsion angle based on the direction of increase or decrease of the torque detected by the sensor 12.
In Fig. 4B, reference numeral 403 denotes the similar hysteresis characteristic (the hysteresis characteristic in the above torque fluctuation range). In Fig. 4B, φ ₁ ' denotes the first torsion angle, and φ ₁ '' denotes the second torsion angle.

As a result, the calculation unit 14 in embodiment 1 is able to estimate a torsion angle equivalent to the actual torsion angle even when torque is not applied up to the rated value to the output side of the strain wave gear reducer 2.
The difference between the two twist angles (first twist angle-second twist angle) is the amount of hysteresis loss.

Next, the control unit 15 controls the actuator 3 based on the rotational position detected by the rotational position detector 11 and the torsion angle calculated by the calculation unit 14 (step ST303). At this time, the control unit 15 controls the actuator 3 by taking into account the position error due to the torsion angle in relation to the rotational position. The control unit 15 corrects the position error of the strain wave gear reducer 2.
By the above operations, the correction system 1 according to the first embodiment is able to correct the position error of the strain wave gear reducer 2.

As described above, according to this embodiment 1, the correction system 1 includes a rotational position detector 11 that detects the rotational position of the actuator 3 that drives the strain wave gear reducer 2, a sensor 12 that detects the torque applied to the output side of the strain wave gear reducer 2, a calculation unit 14 that calculates the hysteresis characteristics in the fluctuation range of the torque based on the hysteresis characteristics in the range of the rated torque for the strain wave gear reducer 2 and the torque detected by the sensor 12, and calculates the torsion angle generated on the output side of the strain wave gear reducer 2, and a control unit 15 that controls the actuator 3 based on the rotational position detected by the rotational position detector 11 and the torsion angle calculated by the calculation unit 14. As a result, the correction system 1 according to embodiment 1 can correct the position error of the strain wave gear reducer 2 even if the torque applied to the output side of the strain wave gear reducer 2 is not up to the rated value. Moreover, the correction system 1 according to embodiment 1 can correct the position error of the strain wave gear reducer 2 with a simpler configuration than the conventional configuration. In other words, the correction system 1 according to the first embodiment does not require an expensive angle rotation position detector as in the conventional second measure, and is not affected by electrical noise, Joule heat, and the temperature characteristics of the motor torque constant as in the conventional third measure, improving the estimation accuracy.

In addition, any of the components of the embodiments of the present invention may be modified or omitted within the scope of the invention.

REFERENCE SIGNS LIST 1 Correction system 2 Harmonic gear reducer 3 Actuator 11 Rotational position detector 12 Sensor 13 Memory unit 14 Calculation unit 15 Control unit 21 Circular spline 22 Wave generator 23 Flexspline

Claims (5)

a rotational position detector that detects a rotational position of an actuator that drives the strain wave gear reducer;
a sensor for detecting a torque applied to an output side of the strain wave gear reducer;
a calculation unit that calculates a hysteresis characteristic within a fluctuation range of the torque based on the hysteresis characteristic within a rated torque range for the strain wave gear reducer and the torque detected by the sensor, and calculates a torsion angle generated on the output side of the strain wave gear reducer;
a control unit that controls the actuator based on the rotational position detected by the rotational position detector and the torsion angle calculated by the calculation unit. The correction system according to claim 1, characterized in that the calculation unit calculates a hysteresis characteristic in the torque fluctuation range detected by the sensor, which is similar to a hysteresis characteristic in the rated torque range for the strain wave gear reducer, from a ratio between the torque fluctuation range detected by the sensor and a rated torque range, and calculates a torsion angle from the hysteresis characteristic in the torque fluctuation range and the torque detected by the sensor. 3. The correction system according to claim 1, wherein the calculation unit calculates a torsion angle based on a direction of increase or decrease in the torque detected by the sensor. a calculation unit that calculates a torsion angle generated on the output side of the strain wave gear reducer based on a hysteresis characteristic within a rated torque range for the strain wave gear reducer and a torque detected by a sensor that detects the torque applied to the output side of the strain wave gear reducer; and
a control unit that controls the actuator based on a rotational position detected by a rotational position detector that detects a rotational position of an actuator that drives the strain wave gear reducer, and on the torsion angle calculated by the calculation unit. a calculation unit calculating a hysteresis characteristic within a fluctuation range of the torque based on the hysteresis characteristic within a rated torque range for the strain wave gear reducer and the torque detected by a sensor that detects the torque applied to the output side of the strain wave gear reducer, and calculating a torsion angle generated on the output side of the strain wave gear reducer;
and a control unit controls the actuator based on a rotational position detected by a rotational position detector that detects the rotational position of an actuator that drives the strain wave gear reducer, and on the torsion angle calculated by the calculation unit.

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