Electromechanical Actuator Wear Detection by Force-Current Monitoring
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Solution Overview
Problem
Actuator systems in safety-critical applications, such as patient lifters, face risks due to wear-related failures, particularly in the spindle nut, worm drive, and bearing, leading to efficiency decreases and potential catastrophic failures, as they fail to maintain load-bearing capabilities, causing accidents or injuries.
Innovation Solution
Incorporating a load cell or piezoelement to measure force and monitor power consumption, calculating the efficiency ratio (force/current) to detect impending failures, enabling preventive replacement and reducing the risk of accidents through online service requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If actuator components are used without monitoring, then device complexity is reduced, but reliability deteriorates due to undetected wear leading to sudden failure
Solution Approach 1:
The patent implements feedback by continuously monitoring current consumption and comparing it against reference values to detect efficiency changes. The control unit receives current signals from the motor, calculates efficiency ratios, and generates alerts when wear is detected, creating a closed-loop monitoring system that improves reliability without requiring complex additional hardware.
Solution Approach 2:
The actuator system performs self-diagnosis by monitoring its own current consumption patterns. The control unit within the actuator calculates efficiency ratios and detects wear conditions internally, allowing the system to monitor itself without requiring external monitoring equipment or complex additional sensors.
2Reliability
If efficiency monitoring is implemented, then reliability is improved through early defect detection, but device complexity increases due to additional sensors and control systems
Solution Approach 1:
The system uses feedback by continuously measuring current consumption and comparing it to reference values stored in memory. The control unit calculates efficiency ratios and generates maintenance alerts when deviations exceed thresholds, enabling predictive maintenance through software-based monitoring rather than complex hardware additions.
Solution Approach 2:
The patent replaces complex mechanical monitoring systems with electrical current measurement and software-based efficiency calculation. Instead of using additional sensors, actuators, or mechanical wear indicators, the system uses the existing motor's current consumption data processed by the control unit to detect wear conditions.
3Productivity
If actuator is operated until failure, then productivity is maintained, but loss of time increases due to unexpected downtime and accidents
Solution Approach 1:
The system performs preliminary action by detecting efficiency degradation before actual failure occurs. The control unit monitors current consumption patterns and generates maintenance alerts in advance, allowing operators to schedule replacements during planned maintenance windows rather than experiencing unexpected downtime.
Solution Approach 2:
Through continuous feedback on current consumption and efficiency ratios, the system provides early warning signs of impending failure. This enables proactive maintenance scheduling that prevents unexpected breakdowns and maintains productivity by avoiding unplanned downtime and potential accidents.
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
The monitoring system effectively anticipates and prevents actuator failures by identifying efficiency changes, allowing for timely replacement, thereby ensuring safety and minimizing downtime in safety-critical applications.
Implementation Method 1
For measuring the force on the rear mounting, a load cell, here a piezoelement 13, may be incorporated in connection with this.
Data Source
Figure 1
AI summary
Today, electromechanical actuator systems are used in a variety of applications, of which some are more safety critical than others. Likewise, they are used in a wide range of applications where the safety of persons often to a higher or lesser extent depends on that the actuators remains safe both during normal use and in the fault conditions, which may occur. By an actuator comprising a DC motor (2) equipped with a worm drive and a spindle (4), the typical wearing components are the bearing, which carries the spindle (4), the spindle nut (5) and the worm wheel (9) in the worm drive. Common to the described defect situations is that they in the time leading up to the occurrence of the defect will show a decrease in the ratio of efficiency. Whether it is the spindle bearing, the worm drive, the spindle nut (5) or for that matter the motor, which is getting worn, the proportion between the current which the motor absorbs and the force the actuator performs will change. The purpose of the present invention is thus to monitor the ratio of efficiency of the actuator. When this begins to change, becomes worse, it is time to replace the actuator before it becomes defective. For this purpose a load cell can for instance be incorporated in the actuator, for measuring the force on the rear mounting. This force is compared with the power consumption and an indicator for the ratio of efficiency can thus be calculated as force/current.