Method for suppressing variation in the rotational speed of an actuator

Abstract

The drive control (1) of an actuator (2) first measures a positioning error of an actuator output shaft (7), caused by the angular transmission error of a wave gear (5), and stores it as correction data (C). In a feedback control loop, a speed feedback value (ωf) is calculated using the measured positioning feedback value θf of the actuator output shaft (7) after it has been corrected by the correction data (C), and a current command (Ir) is calculated using this value to control the drive of a motor (3). Since a speed component caused by the angular transmission error of the wave gear (5) has been added to the speed of a motor with respect to the speed feedback value (ωf), a variation in the speed of the actuator output shaft (7) caused by the angular transmission error of the wave gear (5) can be effectively suppressed.

Description

Technical area

[0001] The present invention relates to a method for suppressing variation in the speed of an actuator, in which variation in the speed of an actuator output shaft caused by an angular transmission error of a wave gear is suppressed in an actuator equipped with the wave gear. The present invention also relates to a drive control of an actuator in which this method for suppressing variation in the speed is applied. State of the art

[0002] Known actuators include designs in which the output rotation speed of a motor is reduced by a wave gear mechanism and a load-side part is held at a target position. The wave gear mechanism is equipped with an annular fixed internally toothed gear, an annular flexible externally toothed gear, and a wave generator. In a typical wave gear mechanism, a state is created in which the flexible externally toothed gear is bent into an elliptical shape by the wave generator, and the outer tooth portions located at both ends of this elliptical shape in the direction of the major axis are engaged with corresponding portions of the inner toothing of the fixed internally toothed gear.Once the motor causes the wave generator to rotate, the meshing positions of the two gears move circumferentially and a relative rotation between the two gears according to the difference 2n (where n is a positive integer) in the number of teeth between the two gears is generated.

[0003] Generally, the difference in the number of teeth between the two gears is two. The fixed internal gear is fixed, and the flexible external gear rotates as one element to output rotation at a reduced speed. The load-side element, connected to the flexible external gear, is driven to rotate at a low speed. The reduction ratio i in this case is represented by the following equation: i=1 / R=(Zc−Zf) / Zf R gear ratio Zf Number of teeth of the flexible, externally toothed gear Zc Number of teeth of the fixed, internally toothed gear

[0004] For example, if Zf = 100 and Zc = 102, then the reduction ratio i=1 / 50 and the output rotation moves in the direction opposite to the direction of rotation of the motor.

[0005] The drive control of an actuator with this design generally controls the actuator's positioning through feedback control. In this case, an angular transmission error occurs in the wave gear. Due to this angular transmission error, an error occurs between the target position and the actual position of the actuator output shaft (the output shaft of the wave gear). The positioning accuracy of the actuator equipped with the wave gear could be improved if this error could be compensated.

[0006] Methods for correcting the positioning error of an actuator are proposed in Patent Documents 1 and 2, which correct the positioning error caused by the angular transmission error of the wave gear and perform precise positioning. Positioning accuracy is improved in Patent Document 1 by adding a correction amount to the positioning feedback, and in Patent Document 2 by adding a correction amount to the positioning command.

[0007] However, due to the effects of an error component in the wave gear, variations in the speed of the actuator output shaft occur in actuators equipped with a wave gear. Such speed variations cannot be suppressed using conventional positioning error correction methods. Patent document 1: JP 2002 - 175 120 A Patent document 2: JP 2003 - 223 225 A Disclosure of the invention

[0008] In view of the problems described above, it is an object of the present invention to propose a method for suppressing variations in the rotational speed of an actuator, which is capable of effectively suppressing variations in the rotation of an actuator output shaft caused by an angular transmission error of a wave gear. It is also an object to propose a drive control system for an actuator in which this method is applied.

[0009] To achieve the above-described objectives, in the present invention, a positioning error of an actuator output shaft caused by an angular transmission error of a wave gear in an actuator equipped with a wave gear is measured in advance; the rotational speed of the actuator output shaft is calculated in a corresponding speed-controlling feedback loop using the result of correcting detected positioning information of the actuator output shaft using the positioning error; and this information is used as a speed feedback value. Alternatively, the result of using the detected positioning error to correct the rotational speed calculated from the detected positioning information is used as the speed feedback value.

[0010] DE 102 06 747 A1 describes a method for position error correction in an actuator having a motor and a shaft gear reduction drive which transmits an output torque of the motor to a load at a reduced speed, comprising the steps of: measuring a position error with respect to an absolute position of an actuator output shaft in order to generate error correction data with respect to a rotational position of the motor shaft; determining a rotational position of the motor shaft; generating rotational position correction information by adding error correction values ​​associated with the rotational position information to the determined rotational position information in the error correction data; and using the generated rotational position error information as position feedback information for controlling the position of the output shaft.

[0011] In other words, in the method for suppressing variation in the rotational speed of an actuator according to the present invention, an absolute position of one revolution of the motor rotation shaft is used as a reference to measure a positioning error of each rotational angular position of an actuator output shaft and calculate error correction data for the actuator output shaft for each of the rotational angular positions of the motor rotation shaft. During drive control, a rotational position of the motor rotation shaft is detected, the error correction data is used to determine an error correction value associated with the detected rotational position, and the rotational speed of the motor rotation shaft is calculated from a value obtained by using the error correction value to correct the rotational position.Alternatively, the speed of the motor rotation shaft calculated from the rotation position is corrected based on the error correction value, and the thus determined speed is used as the speed feedback value for the feedback control of the actuator output shaft.

[0012] In the present invention, the absolute position of one revolution of the motor rotation shaft is used as a reference to measure the positioning error of the actuator output shaft for at least one revolution of the actuator output shaft and to generate error correction data.

[0013] In this case, the positioning errors in the measured rotational positions are averaged, and error correction data representing the error correction values ​​for each of the rotational positions of one revolution of the motor rotation shaft can be generated.

[0014] The error correction data may be generated as a correction pulse data sequence acting as error correction information for each of the rotational positions of one revolution of the motor rotation shaft, or may be generated as a coefficient sequence for an approximate formula representing errors in each of the rotational positions of one revolution of the motor rotation shaft.

[0015] The present invention also relates to a drive controller for an actuator for suppressing variation in rotational speed using the above-described method, the drive controller being characterized by comprising an error correction data storage section in which error correction data is stored; a position detector attached to the motor rotational shaft; and a feedback control section for performing feedback control that causes the actuator output shaft to arrive at a target position determined by position command information that uses, as a rotational speed feedback value, a detection position of the motor rotational shaft detected by the position detector and a rotational speed of the motor rotational shaft calculated based on the error correction data.

[0016] The feedback control section may also perform feedback control so that the actuator output shaft reaches a target speed determined by speed command information.

[0017] In the speed feedback values ​​used for actuator feedback control in the present invention, a speed component generated by the wave gear angular transmission error is added to the speed calculated from the detected position of the motor rotation shaft. Feedback is therefore used to control the speed, and variations in the actuator output shaft speed caused by the wave gear angular transmission error can be effectively suppressed. Short description of the drawings Fig. 1 is a schematic block diagram showing an example of a drive control of an actuator in which the present invention is used; Fig. 2 is a diagram to illustrate the method for generating correction data in the drive control according to Fig. 1 to describe; Fig. 3 is a diagram showing a correspondence table of the correction data that are generated; and Fig. 4 is a schematic block diagram showing another example of a drive control of an actuator in which the present invention is used. List of reference symbols 1.1A drive control 2 actuators 3 Engine 4 Motor rotation shaft 5 wave gears 6 Position detector 7 Actuator output shaft 8 rotation position information 11 Feedback control area 12 Correction data storage area 13 Position control range 14 Speed ​​control range 15 Speed ​​calculation range 16 Current gain range C Error correction data θf position feedback value ωf speed feedback value θr position command ωr speed command Ir current command Best mode for carrying out the invention

[0018] An embodiment of a drive control of an actuator in which the method according to the present invention is used will be described below with reference to the drawings.

[0019] Fig. 1 is a schematic structural diagram showing a drive controller of an actuator according to the present example. An actuator 2 of the present example, driven by the drive controller 1, includes a motor 3, a wave gear 5 connected to a motor rotating shaft 4, and a position detector 6 capable of detecting the rotational position of the motor rotating shaft 4. The output shaft, i.e., the actuator output shaft 7 of the wave gear 5, is connected to a load (not shown). The position detector 6 is a rotary encoder, potentiometer, or other position detector capable of detecting an absolute position.

[0020] The drive controller 1 for controlling the actuator 2 includes a feedback control section 11 for performing feedback control so that the actuator 2 assumes a target position determined by a position command θr from a higher-level device, and a correction data storage section 12 in which error correction data C representing position errors caused by an angular transmission error of the wave gear 5 is stored. In the feedback control section 11, a speed command ωr is calculated in the position control section 13 based on the difference between the position command θr and a position feedback value θf from the position detector 6 and provided to the speed control section 14.In the speed control section 14, a current command Ir is calculated based on the difference between the speed command ωr and a speed feedback value wf provided by a speed calculation section 15 and supplied to a current amplification section 16. A motor drive current is supplied to the motor 3 through the current amplification section 16.

[0021] In the speed calculation section 15, the position feedback value θf provided by the position detector 6 is corrected based on the correction data C, and the speed feedback value ωf is calculated from the corrected value. The corrected value is determined, for example, by adding or subtracting correction data C relative to the position feedback value θf, and the speed feedback value ωf is calculated from the corrected value. The equation for calculating the speed in this case is as follows, where Δt is the sample period: ωf=((θf(t)+C(t))*(θ(t−1)+C(t−1))) / Δt (Correction data)

[0022] The correction data C of the present example is generated as follows. First, the positioning error of the motor rotation shaft 4 in the actuator 2 is reduced by a factor of the reduction ratio of the wave gear 5 due to the reduction of the wave gear 5 connected to the motor rotation shaft. For example, when the gear ratio of the wave gear 5 is 50 or 100, the positioning error of the motor itself is compressed to 1 / 50 or 1 / 100, respectively. Therefore, the positioning error of the actuator is essentially caused by the angular transmission error of the wave gear 5, and therefore, the positioning error of the actuator 2 in a single direction is determined by the angular transmission error of the wave gear 5.

[0023] Positioning is performed continuously in a single rotation direction, and the difference between the actual rotation angle and the intended rotation angle using reference positions is determined for each position. The positioning accuracy in a single direction is the maximum of these values ​​over the course of one rotation.

[0024] The positioning accuracy in a single direction of actuator 2 in this example, i.e., the positioning error of actuator 2, is measured for one revolution of the actuator output shaft 7 based on the absolute position of the motor rotation shaft. For example, if the gear ratio of the strain wave gear 5 is 1 / 50, the output shaft 7 rotates once for every 50 revolutions of the motor rotation shaft 4.

[0025] The positioning error is measured, for example, for every 3° of rotation of the motor rotation shaft 4 on the basis of the output value of the position detector 6, as shown in Fig. 2. In this case, the measurement of the motor rotation shaft 4 is performed at 120 points (360° / 3°), and for the actuator output shaft 7, these 120 points are multiplied by the gear ratio.

[0026] The measured data are essentially the same even when the angular transmission accuracy of the wave gear is used instead of the positioning accuracy in a single direction. It should also be clear that the measurement can be performed not only for one revolution, but also for one or more revolutions of the actuator output shaft 7.

[0027] The error data for each measured point, ie, the error data for 120 places, are averaged and correction data C for one revolution of the motor shaft 4 is generated, as shown in the last row of the table in Fig. 2 shown.

[0028] The format of the generated correction data C can be a correction pulse number for error correction for each of the rotation angle positions in one revolution of the motor rotation shaft 4. Correction pulse numbers, which, as above, have been measured, for example, for every 3°, can be entered into a correspondence table for assigning the rotation positions for every 3° of the rotation of the motor shaft 4, as in Fig. 3 shown.

[0029] Alternatively, the correction data for one revolution of the motor rotation shaft 4 can be developed into a Fourier series, and an approximate curve can be determined. The coefficients of the Fourier series represented by the approximate curve can be stored and saved as correction data C. In this case, an initialization process can be performed when the drive power of the drive controller 1 is turned on, in which the stored coefficients are inserted into the approximate formula to calculate the correction data, and correction pulse data sequences are generated, as shown in Fig. 3 shown.

[0030] In the drive controller 1 of an actuator of the present example described above, a positioning error generated by an angular transmission error of the wave gear 5 is measured in advance, and correction data C representing the positioning error of the rotational positions of the motor rotation shaft 4 is generated. In the feedback control loop for controlling the motor, error correction values ​​for the rotational positions are determined from the correction data C based on the absolute position of the motor rotation shaft 4. The speed feedback value ωf is calculated taking these error correction values ​​into account, and the current command Ir for driving the motor is calculated using this speed feedback value ωf.In the calculated speed feedback value, the speed component caused by the angular transmission error of the wave gear 5 is added to the speed of the motor rotating shaft 4, and the speed is feedback-controlled. Variations in the speed of the actuator output shaft 7 caused by the angular transmission error of the wave gear 5 can thus be effectively suppressed.

[0031] Feedback control is performed in this example based on the position command θr from a higher-level device, but feedback control can also be performed based on the speed command ωr from a higher-level device.

[0032] Fig. 4 is a schematic structural diagram showing an example of a drive control of an actuator in such cases. As in Fig. 4, the position control section 13 is omitted in this drive control 1A, but the rest of the structure is identical to the drive control 1. The same designations are therefore used for the corresponding sections of the Fig. 4 is used. With this design, an operating result can be achieved that is identical to that of the previously described drive control 1.

Claims

[1] Method for suppressing variation in the speed of an output shaft (7) of an actuator (2) which is equipped with a motor (3) and a wave gear (5), wherein the method for suppressing variation in the speed of an actuator (2) characterized by is that it has: Using an absolute position of one revolution of the motor rotation shaft (4) as a reference to measure, for each rotation angle position of the motor rotation shaft (4), a positioning error of each rotation angle position of the actuator output shaft (7) and to generate error correction data (C) for the actuator output shaft (7); Detecting a rotational position of the motor rotation shaft (4); Using the error correction data (C) to determine an error correction value associated with the detected rotation position; Calculating the rotational speed of the motor rotation shaft (4) from a value obtained by using the error correction value to correct the rotational position, or alternatively correcting the rotational speed of the motor rotation shaft (4) calculated from the rotational position on the basis of the error correction value; and Using the determined speed as a speed feedback value for feedback control of the speed of the actuator output shaft (7). [2] Method for suppressing variation in the speed of an actuator (2) according to claim 1, characterized by that it includes using the absolute position of one revolution of the motor rotation shaft (4) as a reference to measure the positioning error of the actuator output shaft (7) for at least one revolution of the actuator output shaft (7) and to generate error correction data (C). [3] Method for suppressing variation in the speed of an actuator (2) according to claim 2, characterized by that it includes averaging the positioning errors of the measured rotational positions and generating error correction data (C) representing error correction values for each of the rotational positions of one revolution of the motor rotation shaft (4). [4] A method for suppressing variation in the rotational speed of an actuator (2) according to claim 3, wherein the method for suppressing variation in the rotational speed of an actuator (2) characterized by is that the error correction data (C) is a correction pulse data sequence serving as error correction information for each of the rotational positions of one revolution of the motor rotation shaft (4), or a coefficient sequence for an approximate formula representing errors in each of the rotational positions of one revolution of the motor rotation shaft (4). [5] Drive control (1, 1A) of an actuator (2) for suppressing variation in the rotational speed using the method according to one of claims 1 to 4, wherein the drive control (1, 1A) of an actuator (2) characterized by is that it has: an error correction data (C) storage area (12) in which error correction data (C) is stored; a position detector (6) mounted on the motor rotation shaft (4); and a feedback control section (11) for performing feedback control to cause the actuator output shaft (7) to arrive at a target position determined from position command information, using as a speed feedback value a detection position of the motor rotation shaft (4) detected by the position detector (6) and a speed of the motor rotation shaft (4) calculated based on the error correction data (C). [6] Drive control (1, 1A) of an actuator (2) for suppressing variation in the rotational speed using the method according to one of claims 1 to 4, wherein the drive control (1, 1A) of an actuator (2) characterized by is that it has: an error correction data (C) storage area (12) in which error correction data (C) is stored; a position detector (6) mounted on the motor rotation shaft (4); and a feedback control section (11) for performing feedback control so as to cause the actuator output shaft (7) to reach a target rotational speed determined by rotational speed command information, wherein, as the rotational speed feedback value, a detection position of the motor rotational shaft (4) detected by the position detector (6) and a rotational speed of the motor rotational shaft (4) calculated based on the error correction data (C) are used.

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