Actuator Cam Follower Positioning Rate-Based Control
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Solution Overview
Problem
Existing two-position actuators, such as those disclosed in U.S. application Ser. No. 14/009,120, are susceptible to improvements in accurately identifying the positioning of a follower on a cam profile, particularly on a lift portion, due to limitations in sensing and control methodologies.
Innovation Solution
An actuator device incorporating a cam and follower assembly with a rotatable cam defining first and second cam surfaces and a lift portion, coupled to an output member, utilizes two sensors and a controller to identify the follower's position on the lift portion based on the rate of change in the output member's position along the output member axis as a function of the cam's rotational position, enabling precise positioning and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If voltage-based sensing methodology is used to determine cam rotational position, then the system is simple to implement, but positioning accuracy deteriorates due to susceptibility to power supply variations and motor speed changes
Solution Approach 1:
The patent replaces the electrical/voltage-based sensing methodology with a rate-based methodology that calculates follower position by measuring the rate of change of cam rotational position. This substitution eliminates dependence on voltage signals that are susceptible to power supply variations and motor speed changes, thereby improving positioning accuracy while maintaining system simplicity through the use of standard rotational position sensors.
Solution Approach 2:
The patent changes the parameter used for position determination from absolute voltage level to rate of change of rotational position. By using the derivative (rate of change) rather than the absolute value, the system becomes insensitive to variations in motor speed and power supply, resolving the contradiction between simplicity and accuracy.
2Speed
If absolute position sensing is used, then the system responds quickly to position changes, but accuracy deteriorates on curved surfaces like the lift portion where position is not uniquely defined
Solution Approach 1:
The patent transitions from static absolute position sensing to dynamic rate-based sensing. By measuring the rate of change of rotational position over time, the system can accurately determine follower position on the lift portion regardless of the cam's rotational speed, maintaining both fast response and high accuracy.
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors the rate of change of cam rotational position and uses this information to determine follower position. This feedback approach allows the system to adapt to varying motor speeds and maintain accurate positioning on the lift portion, resolving the contradiction between response speed and positioning accuracy.
Data Source
AI summary
An actuator device having a motor driven cam, a follower coupled to an output member and driven by the cam, and a controller for controlling operation of the motor. The cam has a first cam surface, a second cam surface and a lift portion between the first and second cam surfaces. The controller is configured to identify a predetermined point on the lift portion as the follower is moved relative to the cam along the lift portion toward the second cam surface. The controller identifies the predetermined point based on a rate of change in the position of the output member along an output member axis as a function of the rotational position of the cam about a cam axis. The controller controls operation of the motor based on the predetermined point to position the follower on the second cam surface.