A vibration suppression method and control system for a dual-encoder flexible joint

Abstract

The present invention discloses a vibration suppression method and control system for a dual-encoder flexible joint. The vibration suppression method is aimed at a joint system in which a flexible joint is equipped with sensors at both the motor end and the load end to obtain kinematic information (angular displacement or angular velocity) of the motor end and the load end respectively. The motor end and load end sensors of the flexible joint described in the embodiment of the present invention are encoders. The method measures the motor end speed and the load end speed respectively through the motor end encoder and the load end encoder, and obtains the rigid body speed by weighted summation of the motor end speed and the load end speed. The error between the obtained rigid body speed and the motor end speed (or the error between the rigid body speed and the load end speed) is fed back to the input of the speed controller after passing through a frequency filter. By correcting the input signal of the speed controller, vibration suppression of the controlled system is achieved. The present invention effectively solves the vibration suppression problem of the dual-encoder flexible joint, and at the same time provides an effective new method for vibration suppression of the flexible joints of collaborative robots.

Description

Technical Field

[0001] The present invention belongs to the technical field of vibration suppression of dual-encoder flexible joints, and in particular relates to a vibration suppression method and control system for dual-encoder flexible joints, which is applied to vibration suppression of dual-encoder flexible joints of collaborative robots, and is also applicable to other flexible joint systems that can directly or indirectly measure kinematic information of the motor end and the load end. Background Art

[0002] With the development of social science and technology, human-machine collaborative robots have gradually entered the industry, service industry and people's daily life. However, "vibration" has always been the core problem of human-machine collaborative robots. For collaborative robots with dual encoder flexible joints, the basis of vibration suppression is mainly to suppress the vibration of their joints. In the prior art, based on the vibration suppression method of equivalent rigid body velocity, the rigid body velocity of its control system is equivalently obtained by the input torque of the joint motor. However, for some flexible joints whose joint motor input end is not equipped with a corresponding torque sensor, this method cannot obtain the input torque of the joint motor, and thus cannot achieve the solution of the rigid body velocity, making the method based on equivalent rigid body velocity unable to be applied to flexible joints without input end torque sensors. This problem needs to be solved urgently. In view of the above shortcomings, the method proposed in the present invention is based on the kinematic information of the flexible joint motor end and the load end to obtain the equivalent rigid body velocity by weighted summation. On the basis of the rigid body velocity, the input of the speed controller is corrected by the error feedback between the rigid body velocity and the vibration velocity, so as to increase the damping of the controlled system to suppress vibration. Summary of the Invention

[0003] The main purpose of the present invention is to provide a vibration suppression method and control system for a dual-encoder flexible joint to overcome the deficiencies in the prior art.

[0004] In order to achieve the aforementioned object of the invention, the present invention adopts the following technical solutions:

[0005] An embodiment of the present invention provides a vibration suppression method for a dual-encoder flexible joint, characterized in that the vibration suppression method includes:

[0006] Measure the motor end speed and load end speed based on sensors;

[0007] The rigid body velocity is calculated based on the rigid body velocity solver according to the motor end velocity and the load end velocity measured by the sensor;

[0008] Based on the frequency filter, the error between the motor end speed or the load end speed and the rigid body speed is subjected to frequency filtering to obtain a pure vibration speed in a specific frequency range, and the pure vibration speed is fed back to the input of the speed controller;

[0009] Based on the motor-end speed or load-end speed feedback of the speed controller, the pure vibration speed fed back by the frequency filter is used to correct the input signal of the speed controller, thereby obtaining the corrected speed controller output, i.e., the motor input torque, which is then used as the input of the dual-encoder flexible joint;

[0010] The vibration suppression method realizes vibration suppression of the flexible joint by correcting the input signal of the speed controller.

[0011] An embodiment of the present invention further provides a vibration suppression system for a dual-encoder flexible joint, characterized in that the vibration suppression system includes: a sensor for measuring the motor end speed and the load end speed, a rigid body velocity solver, a frequency filter, and a velocity controller;

[0012] The rigid body velocity solver is used to calculate the rigid body velocity according to the motor end velocity and the load end velocity measured by the sensor;

[0013] The frequency filter is used to obtain a pure vibration velocity in a specific frequency range after frequency filtering the error between the motor end velocity or the load end velocity and the rigid body velocity, and feed the pure vibration velocity back to the input of the speed controller;

[0014] The speed controller, based on the motor-end speed or load-end speed feedback of the speed controller, uses the pure vibration velocity fed back by the frequency filter to correct the input signal of the speed controller, thereby obtaining a corrected speed controller output, i.e., the motor input torque, and using the motor input torque as the input of the dual-encoder flexible joint;

[0015] The system suppresses vibration of the flexible joint by modifying the input signal of the speed controller.

[0016] Compared with the prior art, the advantages of the present invention include:

[0017] (1) The embodiments of the present invention provide a vibration suppression method for a flexible joint of a dual-encoder dual-mass system. Based on the dual-encoder structural characteristics of the joint, an incremental encoder at the motor end and an absolute encoder at the load end are used to calculate the equivalent rigid body velocity, without the need for additional sensors.

[0018] (2 On the one hand, the embodiment of the present invention provides a vibration suppression method for a flexible joint of a dual-encoder dual-mass system. The controller is simple in design. On the basis of ensuring that the system control bandwidth is not lost, only one control parameter is added to further effectively suppress the vibration, which is convenient for engineering application and implementation.

[0019] (3) On the one hand, an embodiment of the present invention provides a vibration suppression method for a flexible joint of a dual-encoder dual-mass system, which requires identification of the system's dynamic model. At the same time, the accuracy of the system model identification determines the vibration suppression effect of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a control algorithm flow in a typical implementation case of the present invention;

[0021] Figure 2 Schematic diagram of a rigid body velocity solver in a typical embodiment of the present invention;

[0022] Figure 3 is a schematic diagram of a frequency filter in a typical embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of a motor-end speed feedback method in a typical implementation case of the present invention;

[0024] Figure 5 This is a schematic diagram of a load-end speed feedback method in a typical implementation case of the present invention;

[0025] Figure 6 This is a comparison diagram of the control effects of speed feedback control and the method of the present invention in a typical implementation case of the present invention (motor end speed vibration suppression based on the motor end speed feedback control method);

[0026] Figure 7 This is a comparison diagram of the control effects of speed feedback control and the method of the present invention in a typical implementation case of the present invention (load-end speed vibration suppression based on the motor-end speed feedback control method).

[0027] Figure 8 This is a comparison diagram of the control effects of speed feedback control and the method of the present invention in a typical implementation case of the present invention (motor end speed vibration suppression based on the load end speed feedback control method);

[0028] Figure 9 This is a comparison diagram of the control effects of speed feedback control and the method of the present invention in a typical implementation case of the present invention (load-end speed vibration suppression based on the load-end speed feedback control method). DETAILED DESCRIPTION

[0029] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The main purpose is to propose a method and control system for suppressing vibration of a dual-encoder flexible joint. The vibration suppression method uses the feedback of a pure vibration signal to correct the input of the speed controller to increase the damping of the controlled system to achieve vibration suppression (such as Figure 1The vibration suppression method includes: measuring the angular displacement signals of the motor end and the load end through the motor end encoder and the load end encoder respectively, and then obtaining the angular velocity of the motor end and the load end after differential processing (hereinafter referred to as the motor end angular velocity and the load end angular velocity respectively as the motor end velocity and the load end velocity); passing the motor end velocity and the load end velocity through the rigid body velocity solver to obtain the rigid body velocity (as shown in FIG. Figure 2 The error between the obtained rigid body velocity and the motor end velocity, or the error between the rigid body velocity and the load end velocity, is passed through a frequency filter to obtain the pure vibration velocity in a specific frequency range (such as Figure 3 As shown in Figure 2) is fed back to the input of the speed controller, and the input signal of the speed controller is modified to increase the damping of the controlled system, thereby achieving vibration suppression. In the present invention, the motor end speed feedback (as shown in Figure 2) is respectively proposed. Figure 4 as shown) and based on load-side speed feedback (as shown) Figure 5 Vibration suppression method shown in Figure 2.

[0030] This invention provides an effective new method for vibration suppression in dual-encoder flexible joints of collaborative robots. This method can be extended to any joint where both motor-side and load-side speeds can be measured. The following further explains this technical solution, its implementation, and its principles.

[0031] On the one hand, an embodiment of the present invention provides a vibration suppression method for a dual-encoder flexible joint, characterized in that the vibration suppression method includes:

[0032] Measure the motor end speed and load end speed based on sensors;

[0033] The rigid body velocity is calculated based on the rigid body velocity solver according to the motor end velocity and the load end velocity measured by the sensor;

[0034] Based on the frequency filter, the error between the motor end speed or the load end speed and the rigid body speed is subjected to frequency filtering to obtain a pure vibration speed in a specific frequency range, and the pure vibration speed is fed back to the input of the speed controller;

[0035] Based on the motor-end speed or load-end speed feedback of the speed controller, the pure vibration speed fed back by the frequency filter is used to correct the input signal of the speed controller, thereby obtaining the corrected speed controller output, i.e., the motor input torque, which is then used as the input of the dual-encoder flexible joint;

[0036] The vibration suppression method realizes vibration suppression of the flexible joint by correcting the input signal of the speed controller.

[0037] Furthermore, the controlled object joint is equipped with sensors at both the motor end and the load end. The sensor refers to any sensor that can directly or indirectly measure the kinematic information of the motor end and the load end. The kinematic information refers to the angular displacement or angular velocity of the joint.

[0038] Furthermore, the rigid body velocity is obtained by weighted summation of the motor end velocity and the load end velocity, the weight of the motor end velocity is the ratio of the motor end inertia to the total inertia, and the weight of the load end velocity is the ratio of the load end inertia to the total inertia, and the total inertia is the sum of the motor end inertia and the load end inertia.

[0039] Furthermore, the frequency filter includes a high-pass filter, a low-pass filter and a gain adjuster; the cutoff frequencies of the high-pass filter and the low-pass filter are set within a certain range of the vibration frequency that needs to be suppressed, so that the high-pass filter and the low-pass filter form a band-pass filter; the gain adjuster is used to adjust the amplitude ratio of the formed band-pass filter, so that the amplitude ratio of the vibration frequency that needs to be suppressed is ensured to be around 0db, and at the same time its phase has no lead or lag, so that the frequency components in the pure vibration signal screened out mainly correspond to the vibration frequency around 0db.

[0040] Furthermore, when the speed controller is based on the motor end speed feedback, the transfer function P from input to output is m The expression of (s) is as follows:

[0041]

[0042] When the speed controller is based on load-side speed feedback, the transfer function from input to output is P l The expression of (s) is as follows:

[0043]

[0044] Where C is the control parameter of the speed controller; ω r is the system resonance frequency of the controlled object, that is, the system resonance frequency of the dual encoder flexible joint; ω a is the system anti-resonance point frequency of the controlled object, that is, the system anti-resonance point frequency of the dual-encoder flexible joint; s is the variable of the transfer function in the Laplace domain; K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

[0045] On the other hand, an embodiment of the present invention provides a vibration suppression system for a dual-encoder flexible joint, characterized in that the vibration suppression system includes: a sensor for measuring the speed of the motor end and the speed of the load end, a rigid body velocity solver, a frequency filter, and a speed controller;

[0046] The rigid body velocity solver is used to calculate the rigid body velocity according to the motor end velocity and the load end velocity measured by the sensor;

[0047] The frequency filter is used to obtain a pure vibration velocity in a specific frequency range after frequency filtering the error between the motor end velocity or the load end velocity and the rigid body velocity, and feed the pure vibration velocity back to the input of the speed controller;

[0048] The speed controller, based on the motor-end speed or load-end speed feedback of the speed controller, uses the pure vibration velocity fed back by the frequency filter to correct the input signal of the speed controller, thereby obtaining a corrected speed controller output, i.e., the motor input torque, and using the motor input torque as the input of the dual-encoder flexible joint;

[0049] The system suppresses vibration of the flexible joint by modifying the input signal of the speed controller.

[0050] Furthermore, the controlled object joint is equipped with sensors at both the motor end and the load end. The sensor refers to any sensor that can directly or indirectly measure the kinematic information of the motor end and the load end. The kinematic information refers to the angular displacement or angular velocity of the joint.

[0051] Furthermore, the rigid body velocity is obtained by weighted summation of the motor end velocity and the load end velocity, the weight of the motor end velocity is the ratio of the motor end inertia to the total inertia, and the weight of the load end velocity is the ratio of the load end inertia to the total inertia, and the total inertia is the sum of the motor end inertia and the load end inertia.

[0052] Furthermore, the frequency filter includes a high-pass filter, a low-pass filter and a gain adjuster; the cutoff frequencies of the high-pass filter and the low-pass filter are set within a certain range of the vibration frequency that needs to be suppressed, so that the high-pass filter and the low-pass filter form a band-pass filter; the gain adjuster is used to adjust the amplitude ratio of the formed band-pass filter, so that the amplitude ratio of the vibration frequency that needs to be suppressed is ensured to be around 0db, and at the same time its phase has no lead or lag, so that the frequency components in the pure vibration signal screened out mainly correspond to the vibration frequency around 0db.

[0053] Furthermore, when the speed controller is based on the motor end speed feedback, the transfer function P from input to output is m The expression of (s) is as follows:

[0054]

[0055] When the speed controller is based on load-side speed feedback, the transfer function from input to output is P l The expression of (s) is as follows:

[0056]

[0057] Where C is the control parameter of the speed controller; ω r is the system resonance frequency of the controlled object, that is, the system resonance frequency of the dual encoder flexible joint; ω a is the system anti-resonance point frequency of the controlled object, that is, the system anti-resonance point frequency of the dual-encoder flexible joint; s is the variable of the transfer function in the Laplace domain; K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

[0058] (1) Controller design:

[0059] Compared with the traditional speed controller, the method based on motor-end speed feedback in the present invention is to feed back the pure vibration speed in the motor-end speed (the pure vibration speed is the difference between the motor-end speed and the ideal rigid body speed) to the input of the speed controller on the basis of motor-end speed feedback, thereby correcting the input signal of the speed controller, increasing the damping term of the system, and effectively suppressing vibration.

[0060] The difference between traditional speed feedback control alone and the method of the present invention is illustrated here through the transfer function of the two. The input of the transfer function is the error between the desired speed and the motor end speed, and the output is the motor end speed. The transfer function here is expressed in the Laplace domain after Laplace transformation.

[0061] The transfer function from the input to the output using conventional velocity feedback control alone is p m (s) as formula (1):

[0062]

[0063] The transfer function P from the input to the output of the method based on the motor end speed feedback in the present invention is m (s) as formula (2):

[0064]

[0065] Where C is the control parameter of the speed controller, ω r is the system resonance frequency of the controlled object (here is the dual encoder flexible joint), ω a is the system anti-resonance point frequency of the controlled object (here is the dual-encoder flexible joint), s is the variable of the transfer function in the Laplace domain, and K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

[0066] From the transfer functions (1) and (2), it can be seen that the method based on motor-end speed feedback in the present invention increases the system damping term K·C·(ω r 2 / ω a 2 -1)·s, that is, it further suppresses vibration by increasing the system damping.

[0067] Similarly, comparing the conventional speed controller with the load-end speed feedback method of the present invention, the input of the transfer function is the error between the desired speed and the load-end speed, and the output is the load-end speed.

[0068] The transfer function from the input to the output using conventional velocity feedback control alone is p l (s) as formula (3):

[0069]

[0070] The method based on load end speed feedback in the present invention is a transfer function P from the input to the output. l (s) as formula (4):

[0071]

[0072] Where C is the control parameter of the speed controller, ω r is the system resonance frequency of the controlled object (here, the dual-encoder flexible joint), s is the variable of the transfer function in the Laplace domain, and K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

[0073] It can be seen from the transfer functions (3) and (4) that the method based on load-end speed feedback in the present invention adds a system damping term -K·C·s compared to the traditional speed feedback control method. When K is negative, the feedback method also suppresses vibration by increasing the system damping.

[0074] (2) Rigid body velocity solver design:

[0075] The essential difference between the method of the present invention and the traditional speed control method is that the feedback of the pure vibration signal is added, and the input signal of the speed controller can be corrected. Then the key to solving the pure vibration signal is to solve the rigid body velocity first. Therefore, how to obtain the rigid body velocity is another key point of this method. In an embodiment of the present invention, the joint structure contains a motor end encoder and a load end encoder. Here, the rigid body velocity is obtained by weighted summation of the motor end velocity (measured by the motor end encoder) and the load end velocity (measured by the load end encoder). The weight of the motor end velocity is the ratio of the motor end damping to the total damping, and the weight of the load end velocity is the ratio of the load end damping to the total damping. The total damping is the sum of the motor end damping and the load end damping. The schematic diagram is shown as follows. Figure 2 .

[0076] (3) Frequency filter design:

[0077] Frequency filter such as Figure 3 As shown, it includes a high-pass filter, a low-pass filter, and a gain adjuster. The cutoff frequencies of the high-pass filter and the low-pass filter are set within a certain range of the resonant frequency of the controlled system (here, the dual-encoder flexible joint system). In this embodiment, the cutoff frequencies are set within the range of ±2 Hz of the resonant frequency, thereby forming a band-pass filter. The gain adjuster is used to adjust the amplitude ratio of the constructed band-pass filter to adjust the amplitude ratio of the vibration frequency to be suppressed to 0 dB, while ensuring that the phase of the vibration frequency has no lead or lag. In this way, the pure vibration signal only contains frequency components around 0 dB, that is, the specific frequency range.

[0078] (IV) Comparison of control effects:

[0079] Using motor end speed feedback, compared with the traditional speed feedback control method ( Figure 6-7 The dotted line in the figure) and the control method of the present invention ( Figure 6-7 Under the premise of ensuring the same control bandwidth for both, the vibration of the load end speed is suppressed to a vibration range within 10% of the expected step speed ( Figure 6-7 The stabilization time of the method of the present invention can be reduced by 40% compared with the time used by the traditional speed feedback control method, indicating that the vibration suppression effect is effectively improved.

[0080] Using load end speed feedback, compared with the traditional speed feedback control method ( Figure 8-9 The dotted line in the figure) and the control method of the present invention ( Figure 8-9 Under the premise of ensuring the same control bandwidth for both, the vibration of the load end speed is suppressed to a vibration range within 10% of the expected step speed ( Figure 8-9The stabilization time of the method of the present invention can be reduced by 60% compared with the time used by the traditional speed feedback control method, indicating that the vibration suppression effect is effectively improved.

[0081] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A vibration suppression method for a dual-encoder flexible joint, characterized in that: The vibration suppression method comprises: Measure the motor end speed and load end speed based on sensors; The rigid body velocity is calculated based on the rigid body velocity solver according to the motor end velocity and the load end velocity measured by the sensor; Based on the frequency filter, the error between the motor end speed or the load end speed and the rigid body speed is subjected to frequency filtering to obtain a pure vibration speed in a specific frequency range, and the pure vibration speed is fed back to the input of the speed controller; Based on the motor-end speed or load-end speed feedback of the speed controller, the pure vibration speed fed back by the frequency filter is used to correct the input signal of the speed controller, thereby obtaining the corrected speed controller output, i.e., the motor input torque, which is then used as the input of the dual-encoder flexible joint; The vibration suppression method realizes vibration suppression of the flexible joint by correcting the input signal of the speed controller; The rigid body velocity is obtained by weighted summation of the motor end velocity and the load end velocity, where the weight of the motor end velocity is the ratio of the motor end inertia to the total inertia, and the weight of the load end velocity is the ratio of the load end inertia to the total inertia, and the total inertia is the sum of the motor end inertia and the load end inertia; When the speed controller is based on motor end speed feedback, the transfer function from input to output is P m The expression of (s) is as follows: When the speed controller is based on load-side speed feedback, the transfer function from input to output is P l The expression of (s) is as follows: Where C is the control parameter of the speed controller; ω r is the system resonance frequency of the controlled object, that is, the system resonance frequency of the dual encoder flexible joint; ω a is the system anti-resonance point frequency of the controlled object, that is, the system anti-resonance point frequency of the dual-encoder flexible joint; s is the variable of the transfer function in the Laplace domain; K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

2. According to the method described in claim 1, the controlled object joint is equipped with sensors at both the motor end and the load end, and the sensor refers to any sensor that can directly or indirectly measure the kinematic information of the motor end and the load end, and the kinematic information refers to the angular displacement or angular velocity of the joint.

3. According to the method according to claim 1, the frequency filter includes a high-pass filter, a low-pass filter and a gain adjuster; the cutoff frequencies of the high-pass filter and the low-pass filter are set to be within a certain range of the vibration frequency to be suppressed, so that the high-pass filter and the low-pass filter form a band-pass filter; the gain adjuster is used to adjust the amplitude ratio of the formed band-pass filter, so that the amplitude ratio of the vibration frequency to be suppressed is ensured to be around 0db, and at the same time its phase has no lead or lag, so that the frequency components in the pure vibration signal screened out mainly correspond to the vibration frequency around 0db.

4. A vibration suppression system for a dual-encoder flexible joint, characterized in that: The vibration suppression system includes: a sensor for measuring the motor end speed and the load end speed, a rigid body velocity solver, a frequency filter and a velocity controller; The rigid body velocity solver is used to calculate the rigid body velocity according to the motor end velocity and the load end velocity measured by the sensor; The frequency filter is used to obtain a pure vibration velocity in a specific frequency range after frequency filtering the error between the motor end velocity or the load end velocity and the rigid body velocity, and feed the pure vibration velocity back to the input of the speed controller; The speed controller, based on the motor-end speed or load-end speed feedback of the speed controller, uses the pure vibration velocity fed back by the frequency filter to correct the input signal of the speed controller, thereby obtaining a corrected speed controller output, i.e., the motor input torque, and using the motor input torque as the input of the dual-encoder flexible joint; The system suppresses vibration of the flexible joint by correcting the input signal of the speed controller; The rigid body velocity is obtained by weighted summation of the motor end velocity and the load end velocity, where the weight of the motor end velocity is the ratio of the motor end inertia to the total inertia, and the weight of the load end velocity is the ratio of the load end inertia to the total inertia, and the total inertia is the sum of the motor end inertia and the load end inertia; When the speed controller is based on motor end speed feedback, the transfer function from input to output is P m The expression of (s) is as follows: When the speed controller is based on load-side speed feedback, the transfer function from input to output is P l The expression of (s) is as follows: Where C is the control parameter of the speed controller; ω r is the system resonance frequency of the controlled object, that is, the system resonance frequency of the dual encoder flexible joint; ω a is the system anti-resonance point frequency of the controlled object, that is, the system anti-resonance point frequency of the dual-encoder flexible joint; s is the variable of the transfer function in the Laplace domain; K is the gain adjuster in the frequency filter, that is, the feedback gain of the pure vibration signal.

5. According to the system of claim 4, the controlled object joint is equipped with sensors at both the motor end and the load end, and the sensor refers to any sensor that can directly or indirectly measure the kinematic information of the motor end and the load end, and the kinematic information refers to the angular displacement or angular velocity of the joint.

6. According to the system of claim 4, the frequency filter includes a high-pass filter, a low-pass filter and a gain adjuster; the cutoff frequencies of the high-pass filter and the low-pass filter are set to be within a certain range of the vibration frequency to be suppressed, so that the high-pass filter and the low-pass filter form a band-pass filter; the gain adjuster is used to adjust the amplitude ratio of the formed band-pass filter, so as to ensure that the amplitude ratio of the vibration frequency to be suppressed is close to 0db, and at the same time its phase has no lead or lag, so that the frequency components in the pure vibration signal screened out mainly correspond to the vibration frequency close to 0db.

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