Robot Joint Backlash Inspection Using Motor Current Feedback
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Solution Overview
Problem
Long-term use of machines with gear drive units leads to increased backlash, which existing methods struggle to effectively measure and manage, affecting the precision and reliability of the machines.
Innovation Solution
A robot mechanism with a control unit that performs periodic inspection operations on drive units with gears, calculating backlash based on motor current values during specific rotations, and notifying maintenance information to operators for proactive maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If gears are used in drive units for long-term operation, then the machine can operate continuously, but backlash increases over time affecting precision
Solution Approach 1:
The system performs preliminary inspection actions by rotating the joint through a predetermined angle range and measuring motor current before actual operation. This allows detection of backlash changes in advance, enabling maintenance scheduling that prevents precision degradation during long-term operation.
Solution Approach 2:
The system continuously monitors motor current during joint rotation and uses this feedback to calculate backlash values. The notification unit provides feedback to operators about maintenance needs based on measured backlash, creating a closed-loop system that maintains precision over time through informed maintenance decisions.
2Measurement precision
If existing backlash measurement methods are used, then some measurement capability is provided, but measurement precision and reliability are insufficient
Solution Approach 1:
The system replaces complex mechanical measurement devices with an electrical measurement approach. By measuring motor current during controlled joint rotation and calculating backlash from current characteristics, the system achieves precise and reliable measurements without requiring additional mechanical sensors or measurement apparatus.
Solution Approach 2:
The drive unit's own motor serves as the measurement sensor. The motor current, which is already being monitored for control purposes, is repurposed to detect backlash changes. This self-service approach eliminates the need for separate measurement systems while providing continuous monitoring capability.
3Reliability
If periodic inspection operations are implemented, then backlash can be monitored, but operational time is consumed
Solution Approach 1:
The inspection operation uses partial action by rotating the joint through a limited predetermined angle range rather than a full 360-degree rotation. This partial rotation is sufficient to detect backlash changes while minimizing the time consumed. The system performs only the necessary measurement portion of a complete operational cycle.
4Productivity
If maintenance is performed based on actual need rather than schedule, then maintenance resources are optimized, but positional instability may occur
Solution Approach 1:
The notification unit provides feedback to operators about the actual maintenance needs of each drive unit based on measured backlash values. This enables condition-based maintenance where resources are allocated to units that actually need them, optimizing maintenance efficiency while preventing positioning instability in units that have developed excessive backlash.
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
Enables precise measurement and management of backlash in gear drive units, allowing for timely maintenance and preventing positional instability and defects in the robot's operations.
Implementation Method 1
a target drive unit to be inspected, among the plurality of drive units, the drive unit including a motor and a gear
Data Source
AI summary
A robot including a robot mechanism including joints and drive units, a control unit controlling the drive units so that an inspection operation to inspect one target drive unit among the drive units is executed by the robot mechanism, and a notification unit notifying maintenance information of the target drive unit based on a current value of a motor of the target drive unit during the inspection operation, or on information associated with the current value, and the inspection operation includes transmitting, to the motor of the target drive unit, control command to rotate a joint as much as a predetermined rotation angle, and thereby moving a tip of the robot mechanism or a tool at the tip, close to an object at a predetermined position from a predetermined start position, to press the object, and separating the tip of the robot mechanism or the tool away from the object.