Robot Wrist Axis Encoder Contact Detection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing methods for instructing robots to accurately position large-sized semiconductor wafers or glass substrates are skill-dependent and prone to errors due to deformation and unwanted particle generation, leading to reduced accuracy.

Innovation Solution

A robot with a wrist axis drive unit and encoder system that sets the control loop gain to zero before contact, allowing the end effector to detect angular displacement and determine the target position without deformation or particle generation, using a motor and encoder to rotate the wrist axis and control the robot arm's movement in X, Y, and Z directions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the robot is moved at a very low speed to avoid deformation and particle generation, then deformation and particle generation are prevented, but measurement precision deteriorates due to fluctuation factors

Engineering Contradiction:

Improvedeformation and particle generationVSAvoidpositional detection accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent changes the control parameter by setting the control loop gain to zero before contact, transitioning the wrist axis drive unit from a controlled state to a free state. This allows the system to operate without active control interference during the critical contact detection phase, eliminating the trade-off between speed and accuracy.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional torque/speed-based contact detection method with an encoder-based angular displacement detection method. By using the encoder to directly measure the angular position of the wrist axis, the system achieves high-precision contact detection without relying on low-speed operation, thus eliminating deformation and particle generation while maintaining measurement accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Difficulty of detecting and measuring

If conventional torque and speed detection methods are used to detect contact, then contact point can be detected, but deformation and unwanted particles are generated

Engineering Contradiction:

Improvecontact point detectionVSAvoiddeformation and particle generation

Core Design Contradiction:

Difficulty of detecting and measuringVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes the mechanical torque/speed detection method with an encoder-based angular displacement detection system. The encoder directly measures the angular position of the wrist axis, providing contact point detection without requiring forceful contact that causes deformation and particle generation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces the encoder as an intermediary measurement device between the wrist axis and the detection system. Instead of directly measuring torque and speed that require significant contact force, the encoder provides an indirect but accurate measurement of contact through angular displacement, eliminating harmful contact effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If high speed operation is used to improve productivity, then productivity increases, but contact detection accuracy deteriorates due to fluctuation factors

Engineering Contradiction:

Improveoperation speedVSAvoidcontact detection accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent replaces the torque/speed-based detection system with an encoder-based angular displacement detection system. This substitution allows contact detection to be performed accurately regardless of operation speed, as the encoder provides direct angular position measurement without being affected by the fluctuation factors that plague high-speed torque and speed measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 method enables high-accuracy detection of the target position without deforming the end effector or generating unwanted particles, reducing the impact of fluctuation factors and ensuring precise positional data for real operational conditions.

Implementation Method 1

an encoder is provided to the motor, and the robot control unit detects an angular displacement of the wrist axis by changes of a position of the encoder

Methodology Applied

Scientific EffectEncoder position detection:

Data Source

PatentEP2308657B1Robot and its teaching method

Publication Date: 2019.09.04 KAWASAKI JUKOGYO KK

Figure 1
Figure 2~3
Figure 4

AI summary

A robot of the invention includes a robot arm (28) having a distal end to which a wrist axis (27) is rotatably provided; arm drive unit (29, 30), each configured to move the robot arm (28); a wrist axis drive unit (31) configured to rotate the wrist axis (27); and a robot control unit (40) configured to control the arm drive unit (29, 30) and wrist axis drive unit (31). The robot control unit (40) is configured to control the arm drive unit (29, 30) to move the distal end of the robot arm (28) to bring a contact member (50) attached to the wrist axis (27) into contact with an instruction target (51), thereby detecting a posture of the robot arm (28) and an angular position of the wrist axis (27) when the wrist axis (27) begins to be angularly displaced due to the contact between the contact member (50) and the instruction target (51), thus determining a position of an instruction point.