Servo Control Apparatus with Proportional Term Filter
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Solution Overview
Problem
In servo control systems, the difference in processing periods for proportional and integral terms leads to oscillations in the command values, particularly when the speed command value is updated, causing disturbances such as 500 Hz, 1 kHz, or 2 kHz oscillations.
Innovation Solution
A servo control apparatus that includes an internal division processing unit to divide the first command value by the period of the proportional term creation unit, and optionally incorporates a timing adjustment unit to advance the timing of the feedforward term, thereby reducing oscillations by synchronizing the calculation periods and adjusting for delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the proportional term is calculated at a shorter period than the integral term, then the responsiveness of the servo control is improved, but oscillations occur in the command values due to period mismatch
Solution Approach 1:
The command value is divided by the ratio of calculation periods in advance before being used in the proportional term calculation. This preliminary division synchronizes the effective sampling rate of the proportional term with the integral term update rate, preventing oscillations while maintaining high-speed calculation capability.
Solution Approach 2:
The calculation period of the proportional term is changed to be shorter than the integral term period, but the command value is scaled by dividing it by the period ratio. This parameter transformation allows the system to benefit from faster calculation while eliminating the harmful oscillation effect.
2Measurement precision
If the calculation period for the proportional term is shortened, then the control accuracy is improved, but the command value oscillates depending on the update period
Solution Approach 1:
The command value is pre-divided by the period ratio before entering the proportional control calculation. This preliminary action ensures that the proportional term contributes to control accuracy without generating oscillations, as the division synchronizes the effective update rate with the integral term.
Solution Approach 2:
The period ratio division acts as an intermediary transformation of the command value. This intermediary step decouples the beneficial effect (faster calculation) from the harmful effect (oscillation), allowing the system to achieve high accuracy without instability.
3Productivity
If different calculation periods are used for proportional and integral terms, then processing efficiency is improved, but synchronization problems arise causing oscillations
Solution Approach 1:
The control calculation is segmented into two distinct processes: the integral term calculated at a longer period and the proportional term calculated at a shorter period. The command value division by period ratio serves as a synchronization mechanism that allows these segmented calculations to work together without causing oscillations.
Solution Approach 2:
The command value parameter is transformed by dividing it by the period ratio, which adjusts its effective frequency content to match the integral term update rate. This parameter change enables efficient multi-rate processing while maintaining signal stability.
Data Source
AI summary
A servo control apparatus includes a subtractor configured to calculate a difference between a first command value for controlling a servo motor, and a first detection value from the servo motor; an integral term creation unit configured to create an integral term based on an output of the subtractor; an internal division processing unit configured to internally divide the first command value; a subtractor configured to calculate a difference between an output of the internal division processing unit and the first detection value; a proportional term creation unit configured to create a proportional term based on the subtractor; and a adder configured to add an output of the integral term creation unit and an output of the proportional term creation unit, in which a calculation period calculated by the proportional term creation unit is shorter than a calculation period calculated by the integral term creation unit.