Electric Gripper Stall Detection Using Back-EMF and Compliance
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Solution Overview
Problem
Existing electric gripper systems are costly and complex, requiring sophisticated controllers to operate, which is not cost-competitive with pneumatic grippers and lacks simplicity in control mechanisms.
Innovation Solution
A compliant stepper motor drive system with a stall-detecting controller and compliance device that uses back electromagnetic field voltage to generate predictable and repeatable force without encoders or sensors, allowing the stepper motor to operate at varying torque and speed to grip objects effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electric gripper systems use sophisticated controllers to operate, then gripping control precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses the stepper motor's own back-EMF signal for stall detection and gripping force control, eliminating the need for external sensors or complex controllers. The motor's electrical characteristics are exploited to provide self-diagnostic capability for detecting load conditions and controlling gripping force.
Solution Approach 2:
The patent replaces mechanical sensing systems (encoders, sensors, complex controllers) with an electrical field-based detection method by monitoring the back-EMF voltage of the stepper motor. This substitution simplifies the system while maintaining control precision.
2Ease of manufacture
If pneumatic grippers are used, then cost is reduced and simplicity is improved, but adaptability to non-fluid environments deteriorates
Solution Approach 1:
The patent replaces pneumatic/hydraulic actuation systems with electric stepper motor actuation. This allows electric grippers to achieve cost-competitiveness and simplicity comparable to pneumatic systems while being adaptable to environments where fluid is not optimal.
3Reliability
If stepper motors operate continuously to maintain grip force, then reliability is improved, but energy consumption increases
Solution Approach 1:
The system uses periodic pulsed operation of the stepper motor instead of continuous operation. The motor is activated only when gripping force needs to be established or adjusted, and relies on mechanical compliance and friction to maintain grip during idle periods, significantly reducing energy consumption while maintaining reliability.
Solution Approach 2:
The patent converts the traditionally harmful effect of compliance (which causes motor stall) into a beneficial feature that enables passive grip force maintenance. The compliance mechanism allows the system to hold grip without continuous power by utilizing elastic deformation and friction.
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 system provides a cost-effective and simple control mechanism for electric grippers, enabling them to compete with pneumatic grippers in terms of cost and complexity while maintaining reliable gripping force without continuous power consumption.
Implementation Method 1
The compliance device 16 deflects and, like a spring develops a force proportional to its deflection.
Implementation Method 2
The controller (control module) that may detect when the stepper motor is approaching its stall torque without using an encoder or sensor by monitoring the back electromagnetic field voltage (EMF) of the motor.
Implementation Method 3
The controller can provide further braking by shorting the motor coils, thus creating a back-EMF brake.
Data Source
AI summary
A gripping device has a body with a stepper motor positioned within the body. A lead screw is driven by the stepper motor. A gripper is coupled with the lead screw for gripping and releasing a part. A compliance enables movement of the motor with respect to the body. A controller is electrically coupled with the motor to provide motion control and maintain a set of learned positions based on sensing when the motor is approaching its stall torque.