Stepping Motor Step-Out Detection Grace Time Control
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Solution Overview
Problem
Stepping motors in robot arm sections often experience 'step-out' conditions due to overloads or sudden speed changes, leading to synchronization issues between pulse signals and actual motor rotations, which can result in unnecessary stopping and reduced operational efficiency.
Innovation Solution
A robot arm section with a stepping motor control system that includes a step-out detection unit, encoder for position tracking, and a motor driver that postpones stopping the motor for a predetermined 'grace time' if the step-out condition does not recover within that time frame, allowing for continued operation if the issue is temporary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stepping motor is stopped immediately when a step-out is detected, then the positioning accuracy is maintained, but the operational efficiency and continuity are reduced
Solution Approach 1:
The control device dynamically adjusts the stopping decision based on real-time evaluation of step-out causes and current motor state. Instead of a static immediate-stop response, the system evaluates whether the step-out was caused by temporary factors (e.g., startup transient, brief overload) and continues operation if recovery is likely, while stopping only when necessary to maintain positioning accuracy.
Solution Approach 2:
The control device uses feedback from the encoder and step-out detection unit to continuously monitor the motor's actual position versus target position. This feedback loop enables the system to detect step-outs, evaluate their causes, and make informed decisions about whether to continue or stop operation, balancing positioning accuracy with operational continuity.
2Productivity
If the stepping motor continues operation after step-out detection, then the operational efficiency is improved, but the positioning accuracy may deteriorate
Solution Approach 1:
The encoder provides continuous feedback on the motor's actual position, allowing the control device to monitor whether the motor has recovered from the step-out condition. If the feedback shows the motor has realigned with the target position, operation continues; if the mismatch persists, the system stops to preserve positioning accuracy.
Solution Approach 2:
The system dynamically transitions between continuous operation and stopping states based on real-time evaluation of positioning accuracy. The control device adjusts its behavior adaptively, continuing operation when positioning remains acceptable and stopping only when necessary to correct positioning errors.
3Productivity
If a grace time period is implemented before stopping the motor, then unnecessary stopping is reduced, but the response time to actual errors is delayed
Solution Approach 1:
The control device performs preliminary evaluation of the step-out condition during the grace time period, analyzing the cause and severity before making a final stopping decision. This preliminary assessment allows the system to distinguish between temporary disturbances that will self-correct and serious errors requiring immediate intervention, reducing unnecessary stopping while maintaining rapid response to actual problems.
Data Source
AI summary
An object of the present invention is to prevent unnecessary driving stop of a stepping motor. A robot arm section includes a robot arm, a stepping motor 31a, a motor driver 31b, an encoder 31c and a step-out detection section 31e. The robot arm has a joint J1. The stepping motor generates power for operating the joint. The motor driver drives the stepping motor according to a target angle. The encoder outputs an encoder pulse every time a drive shaft of the stepping motor rotates by a predetermined angle. The step-out detection section detects a step-out of the stepping motor based on the target angle and a current angle of the stepping motor that is identified based on the encoder pulse. When the stepping motor does not recover from the step-out before a predetermined grace time elapses from a time at which the step-out is detected, the motor driver stops driving the stepping motor at the time point at which the grace time elapses.