Tendon Tensioning via Pulse Current Control
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Solution Overview
Problem
Dexterous robots require precise tension control of tendons to maintain gripping force, but existing systems struggle to efficiently transition and maintain tension levels, leading to inefficiencies in actuation and potential loss of grip.
Innovation Solution
A tendon tensioning system that includes a motor controller configured to apply an initial current to achieve stall tension, followed by a pulse current to boost tension, and then a holding current to maintain the boosted tension level, ensuring consistent grip force without excessive power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If continuous high current is applied to maintain tendon tension, then gripping force is maintained, but power consumption increases
Solution Approach 1:
The system applies periodic pulse currents to the actuator to maintain tendon tension. Instead of continuous high current, the controller delivers intermittent pulse currents that periodically boost the tendon tension back to the desired level after natural relaxation, significantly reducing average power consumption while maintaining gripping force.
Solution Approach 2:
The system dynamically changes the electrical current parameters applied to the actuator. The controller switches between different current levels: a baseline holding current to maintain minimal tension, and periodic pulse currents with higher amplitude to restore tension after relaxation. This parameter switching optimizes the balance between gripping force maintenance and power consumption.
2Use of energy by moving object
If tendon tension is allowed to relax, then power consumption decreases, but gripping force is lost
Solution Approach 1:
The controller implements periodic monitoring and actuation cycles. The system allows the tendon tension to naturally relax during intervals, reducing power consumption, then applies periodic pulse currents to restore tension to the required level. This periodic cycle maintains gripping force while minimizing energy usage during the relaxation intervals.
Solution Approach 2:
The system utilizes the natural elastic properties of the tendon to maintain tension during relaxation phases without active actuation. The tendon's elasticity allows it to maintain residual tension during power-saving intervals, and the actuator only intervenes periodically to restore tension when it drops below the threshold, making the system self-regulating.
3Speed
If rapid tension transition is implemented, then response speed improves, but system stability deteriorates
Solution Approach 1:
The controller uses periodic pulse delivery with carefully controlled timing and duration. Each pulse is delivered at optimal intervals to restore tension without causing overshoot or oscillation. The periodic nature of the control allows the system to achieve rapid response when needed while maintaining stability through consistent, predictable actuation cycles.
Solution Approach 2:
The system applies pulse currents that are sufficient to restore tension to the desired level but not excessive enough to cause overshoot or instability. The controller precisely controls pulse duration and amplitude to achieve just enough tension restoration, avoiding the harmful effects of excessive action while maintaining rapid response capability.
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 effectively maintains a high tension level in the tendon with reduced power usage, allowing for precise control and reliable actuation of dexterous robotic fingers, enhancing the robot's ability to interact with objects and maintain grip without slacking.
Implementation Method 1
an actuator, configured to apply a tension through the tendon in response to an electrical current... The actuator may include a drive screw and a motor
Implementation Method 2
The drive screw of the actuator may include a ball screw, with a ball nut disposed about the ball screw and coupled with the tendon
Data Source
AI summary
A tendon tensioning system includes a tendon having a proximal end and a distal end, an actuator, and a motor controller. The actuator may include a drive screw and a motor, and may be coupled with the proximal end of the tendon and configured to apply a tension through the tendon in response to an electrical current. The motor controller may be electrically coupled with the actuator, and configured to provide an electrical current having a first amplitude to the actuator until a stall tension is achieved through the tendon; provide a pulse current to the actuator following the achievement of the stall tension, where the amplitude of the pulse current is greater than the first amplitude, and return the motor to a steady state holding current following the conclusion of the pulse current.