Hydraulic Motor Speed Control via Load-Based Current Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In oil pressure units with directly connected motors, large increases in oil pressure lead to increased load torque, causing motor speed control to struggle with following stepwise speed commands, resulting in potential motor speed lowering and instability due to noise components from discrete rotation speed information and physical limitations of microcomputer processing speed.
Innovation Solution
An oil pressure unit with an inverter, load sensor, rotation sensor, current command value calculation means, and correction means that adjusts the current command value based on detected load to maintain motor speed convergence, using a correction coefficient or data table to enhance motor speed followability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PI control with standard control period is used, then device complexity is kept low, but motor speed followability deteriorates when load torque drastically increases
Solution Approach 1:
The correction means performs preliminary action by calculating the correction value based on load torque before the motor speed deviation becomes significant. The system predicts the required current command value adjustment in advance using the load torque information, preventing speed lowering before it occurs rather than reacting after the deviation happens.
Solution Approach 2:
The correction value acts as an intermediary that bridges the gap between load torque changes and current command value adjustments. Instead of directly reacting to speed deviations, the system uses load torque as an intermediate parameter to predict and compensate for upcoming speed changes, improving followability without increasing control complexity.
2Speed
If microcomputer processing speed is increased to shorten control period, then motor speed followability improves, but device complexity and cost increase
Solution Approach 1:
The system replaces the need for high-speed mechanical/electronic processing with a computational approach using load torque information. Instead of increasing microcomputer processing speed to achieve faster control, the invention substitutes the processing requirement with a correction mechanism that uses load torque data to predict and compensate for speed deviations, achieving fast response without hardware upgrades.
3Speed
If load torque is estimated from differentiated rotation speed, then speed control responsiveness improves, but measurement precision deteriorates due to noise
Solution Approach 1:
Instead of estimating load torque from rotation speed (which requires differentiation and introduces noise), the system inverts the approach by directly using load torque detection to determine the correction value. This reverse approach eliminates the need for differentiation while maintaining responsiveness to load changes.
4Speed
If speed control gain is increased to improve response to load variation, then motor speed followability improves, but stability deteriorates due to oscillation
Solution Approach 1:
The correction means performs preliminary compensation based on load torque before speed deviations and oscillations occur. By calculating the required current adjustment in advance using load information, the system prevents the need for high gain that would cause oscillation, achieving both responsiveness and stability.
Solution Approach 2:
The system uses load torque feedback to continuously adjust the current command value. This feedback mechanism allows the control system to adapt to load variations smoothly without requiring high gain, maintaining stability while improving followability through continuous correction based on actual load conditions.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
In the present invention, an oil pressure unit includes an inverter 14 for supplying electric power to a motor 15; a load sensor 17 for detecting a load of the oil pressure pump 16A; a rotation sensor 19 for detecting a rotation speed of the motor 15; a current command value calculation means 12 for calculating a current command value so that a deviation between a speed command value representing a target rotation speed of the motor 15 and a rotation speed of the motor 15 converges to zero; a correction means 18A for correcting the current command value based on the load of the oil pressure pump 16A; and a control signal generation means for outputting a control signal to the inverter 14 based on a corrected current command value.