Servomotor Backlash Detection via Torque Peak Analysis
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Solution Overview
Problem
Numerical control machine tools face challenges in accurately detecting and compensating for backlash due to lost motion when the motor is reversed, leading to reduced processing precision and increased inconvenience, especially as the usage environment changes, without effective methods to adjust for varying conditions such as workpiece weight and lubrication.
Innovation Solution
A method is introduced to automatically detect backlash by stepping-transferring the output shaft of a servomotor, measuring and recording torque, and determining the backlash value based on torque peaks without additional positioning detection equipment, allowing for correction of the detected backlash value within the existing numerical control apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If pre-load of the ball screw-nut is increased to raise stiffness, then stiffness of the rotating shaft is improved, but lost motion due to friction is increased
Solution Approach 1:
The system performs preliminary action by detecting backlash before actual machining operations. The automatic backlash detection function measures the backlash value in advance under various usage conditions (different workpiece weights, lubrication states), and stores correction values that will be applied during machining to compensate for the friction-induced lost motion.
Solution Approach 2:
The invention changes parameters by dynamically adjusting the backlash correction value based on detected usage conditions. The system modifies the correction parameter according to the detected workpiece weight and other environmental factors, allowing the machine tool to adapt to varying friction conditions while maintaining the high stiffness provided by increased pre-load.
2Manufacturing precision
If manual measurement and correction of backlash is performed whenever usage environment changes, then processing precision is maintained, but operation convenience deteriorates
Solution Approach 1:
The system implements self-service by automatically detecting backlash and generating correction values without user intervention. The automatic backlash detection function continuously monitors usage conditions (workpiece weight, lubrication state) and autonomously adjusts the backlash correction parameter, eliminating the need for manual measurement and correction operations while maintaining processing precision.
Solution Approach 2:
The invention employs feedback by continuously monitoring usage conditions and automatically adjusting backlash correction based on detected changes. The system measures the actual backlash under current operating conditions and feeds this information back to update the correction value, creating a closed-loop system that maintains precision without requiring manual intervention.
3Measurement precision
If additional positioning detection equipment is added to detect backlash accurately, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses an intermediary approach by employing the existing servomotor's torque characteristics as a mediator to detect backlash. Instead of adding dedicated positioning detection equipment, the invention utilizes the torque sensor or current detector already present in the servomotor system to indirectly measure backlash through torque variations during direction reversal, achieving accurate detection without increasing device complexity.
Solution Approach 2:
The invention demonstrates multi-functionality by making the existing servomotor system serve dual purposes: both driving the ball screw and detecting backlash. The same torque sensor used for motor control is also utilized to measure backlash by detecting torque peaks during direction reversal, eliminating the need for separate detection equipment while maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and automatic detection and correction of backlash, improving processing precision and convenience without increasing the overall cost of the machine tool, as demonstrated by high accuracy in test results across various machine tool models.
Implementation Method 1
a servomotor or other rotation driving sources into linear motion by means of a power transmission mechanism
Implementation Method 2
a ground ball-nut lead screw
Implementation Method 3
the lost motion occurs due to a phenomenon that the workpiece does not immediately reach the instructed position, but only the ball screw and the coupling are wound up or twisted. The lost motion is increased as frictional force, which occurs by a relative motion with respect to a guide surface in the transfer system of the machine tool, and frictional force at the ball-nut lead screw become larger
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
According to the present invention, a torque variation of a servomotor 11, which is measured in a numerical control (NC) apparatus of an existing numerical control (NC) machine tool, is observed, and a backlash is detected by calculating a transfer distance of an output shaft 11a of the servomotor 11 at a torque peak, without adding additional positioning detection equipment, thereby detecting an accurate backlash amount without adding additional equipment.