Servo Feedforward Compensation for Corner Tracking and Vibration
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Solution Overview
Problem
Existing servo control devices face challenges in independently designing gain and phase characteristics for feedforward compensation, leading to vibration and trajectory errors, especially at corners and sudden changes in reference trajectory directions.
Innovation Solution
A servo control device with a feedforward compensation unit that uses a transfer function with unstable zeros, allowing for independent design of gain and phase characteristics, and includes a feedforward characteristics setting unit to determine parameters that minimize trajectory errors and vibration by shaping the position, velocity, and torque feedforward signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is used to smooth the command signal locally on a time basis to suppress machine vibration, then vibration is suppressed, but a trajectory error such as an inward turning error occurs because the response trajectory deviates from the reference trajectory
Solution Approach 1:
The invention applies preliminary action by estimating the future end effector position at a predetermined sampling time ahead and using this estimated position to calculate the correction amount in advance. This allows the correction to be applied proactively before the trajectory error occurs, rather than reactively after the error has manifested. The feedforward compensation unit calculates the correction amount based on the estimated future position, enabling the system to anticipate and correct trajectory deviations before they affect the actual position.
Solution Approach 2:
The invention implements feedback by using the estimated end effector position to calculate a correction amount that is fed back to adjust the command position. The feedforward compensation unit continuously estimates the future position, calculates the deviation from the reference trajectory, and generates a correction signal that is applied to the command position. This closed-loop estimation and correction mechanism ensures that trajectory errors are systematically compensated while maintaining vibration suppression.
2Device complexity
If the gain characteristic and phase characteristic of feedforward compensation are designed together, then the design process is simpler, but it is impossible to independently optimize both characteristics to minimize both trajectory error and vibration
Solution Approach 1:
The invention applies segmentation by separating the feedforward compensation transfer function into independent gain and phase characteristic components. The feedforward compensation unit is designed with distinct parameters for gain characteristic (affecting trajectory accuracy) and phase characteristic (affecting vibration suppression). This segmentation allows each characteristic to be optimized independently through separate parameter adjustments, enabling simultaneous minimization of both trajectory error and vibration without compromising design simplicity.
3Manufacturing precision
If correction amount is calculated using a perpendicular from estimated end effector position to reference trajectory, then trajectory error can be minimized, but in cases where multiple perpendiculars exist (e.g., at corner portions), the correction amount cannot be uniquely determined and may change sharply causing vibration
Solution Approach 1:
The invention applies dynamics by using a dynamic estimation model that continuously predicts the future end effector position based on the system's response characteristics. Instead of using static geometric perpendicular calculations that may yield multiple solutions at corner portions, the dynamic estimation provides a unique, continuous correction amount that smoothly varies with the reference trajectory. This dynamic approach ensures that even at corner portions where multiple perpendiculars could exist, the correction amount remains uniquely determined and changes smoothly, preventing vibration while minimizing trajectory error.
Data Source
AI summary
A servo control device for controlling an end effector of a machine to follow a set reference trajectory by driving the machine using an actuator includes a feedforward compensation unit that performs feedforward compensation by outputting a feedforward signal for controlling the actuator on the basis of a position command signal inputted thereto, wherein input-output characteristics represented in a continuous-time system of the feedforward compensation unit are expressed by a transfer function having unstable zeros, and a step response of the feedforward compensation unit has an initial undershoot.