Linear Actuator Power Limiting for Changing Load Geometry
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Solution Overview
Problem
Existing linear electric actuator systems fail to adequately safeguard both the actuator and the mechanical components of the application against overload, as the protection mechanisms do not account for the varying geometry and dynamic movement, leading to potential hazardous situations where the actuator can exert excessive force beyond permissible limits, even if the current draw does not exceed safety settings.
Innovation Solution
A linear electric actuator system that includes a power limiting circuit capable of adjusting its power limit values based on the position of the spindle nut on the spindle, with programmed values stored in a controller, ensuring that the power supplied does not exceed safe thresholds, even when the load direction changes relative to the actuator's force line, thus protecting both the actuator and mechanical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power limit value is increased to allow higher lifting capability, then the actuator can handle heavier loads, but the mechanical construction may be overloaded when the load is directed in the line of force
Solution Approach 1:
The patent applies local quality by implementing position-specific power limit values. Instead of using a single uniform power limit for all positions, the system programs different power limit values for different positions of the spindle nut on the spindle. This allows the power limit to be locally optimized for each position, permitting higher power when the geometry is favorable and reducing it when the mechanical construction is more vulnerable to overload.
2Reliability
If a calibration cycle is performed to determine maximum current draw, then overload protection is provided, but the protection only safeguards the linear actuator and not the mechanics of the application
Solution Approach 1:
The patent extends the calibration approach by performing calibration at multiple positions of the spindle nut on the spindle rather than at a single position. The power limiting circuit is configured to change the power limit value according to the spindle nut position based on calibrated values for each position, ensuring that the mechanics of the application are safeguarded throughout the entire range of motion, not just at one calibration point.
Data Source
AI summary
A linear electric actuator system, preferably for patient lifters, comprising at least one linear electric actuator and a controller having a power limiting circuit for limiting the power to the at least one linear electric actuator. The actuator system is arranged such that the threshold value of the maximum permissible power in the power limiting circuit may be changed, and that this change may be performed via reference to the position of the spindle nut on the spindle as a look up in a table showing a corresponding value for the power limit.