Electro-pneumatic Controller Slew Limiting for Position Accuracy

Solution Overview

Problem

Electro-pneumatic controllers exhibit asymmetric control responses due to high inductance in solenoids and noise in control and feedback signals, leading to position control accuracy degradation in pneumatic actuators.

Innovation Solution

Implementing a noise detector and drive current slew limiter to determine a slew limit based on noise levels, comparing the difference between calculated and previous drive values, and adjusting the drive value to ensure changes do not exceed this limit, thereby correcting asymmetric control responses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the controller responds quickly to control signals, then the response speed is improved, but position control accuracy deteriorates due to asymmetric control responses caused by high inductance and noise

Engineering Contradiction:

Improveresponse speedVSAvoidposition control accuracy

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The slew limit is dynamically adjusted based on the absolute value of the previous drive value. When the previous drive value is large, a larger slew limit is applied; when it is small, a smaller slew limit is applied. This dynamic adjustment allows the controller to respond quickly when large position changes are needed while maintaining accuracy when small adjustments are required

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The controller changes the slew limit parameter based on operating conditions (previous drive value magnitude). This parameter adaptation resolves the contradiction by allowing different response characteristics depending on the current state, enabling both fast response and high accuracy under different conditions

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the controller allows large changes in drive value, then the productivity is improved, but control precision deteriorates due to asymmetric control responses and noise

Engineering Contradiction:

Improveoperation speedVSAvoidposition control accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The slew limit is dynamically adjusted based on the absolute value of the previous drive value. When the previous drive value is large, a larger slew limit is applied; when it is small, a smaller slew limit is applied. This dynamic adjustment allows the controller to respond quickly when large position changes are needed while maintaining accuracy when small adjustments are required

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

Different slew limit values are applied based on the local operating condition (magnitude of previous drive value). This local quality approach allows large drive value changes when needed for productivity while restricting small changes to maintain precision, resolving the contradiction between productivity and precision

Inventive Principle:

Principle #3Local quality

3Device complexity

If the controller uses fixed slew limit, then the device complexity is reduced, but control accuracy deteriorates due to inability to compensate for noise and asymmetric responses

Engineering Contradiction:

Improvecontrol algorithm complexityVSAvoidposition control accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The controller changes the slew limit parameter based on operating conditions (previous drive value magnitude). This parameter adaptation resolves the contradiction by allowing different response characteristics depending on the current state, enabling both fast response and high accuracy under different conditions

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9063540B2Methods and apparatus to limit a change of a drive value in an electro-pneumatic controller

Publication Date: 2015.06.23 FISHER CONTROLS INT LLC

AI summary

Example methods and apparatus to limit a change of a drive value in an electro-pneumatic controller are disclosed. A disclosed example method includes determining a slew limit of a controller based on noise in at least one of a control signal or a feedback signal, calculating a drive value based on the control signal and the feedback signal, and changing the calculated drive value if a difference between the drive value and a previous drive value is greater than the slew limit of the controller.