Electrostatic Clutch-Based Mechanical Multiplexer with Increased Force Capability

TL;DR

This paper tackles the high actuator count problem in high-DoF robots by introducing an electrostatic capstan clutch-based mechanical multiplexer that supports both SIMO and SISO control from a single motor. It combines JRCC-based electrostatic clutches with leadscrews, enabling four outputs to be driven either concurrently or sequentially through tiling units along shared input shafts. The approach yields substantial performance gains, including up to 212 N per output, a 4.09× increase in vertical grip, and a 354% increase in horizontal carrying capacity, demonstrated on a four-DoF tendon-driven robotic hand and with a drill task. The work demonstrates a viable path to reducing actuator count and weight in complex robotic systems, with potential impact on cable-driven robots, haptic displays, and scalable actuation networks, while noting limitations in backdrivability and velocity control that guide future optimization.

Abstract

Robotic systems with many degrees of freedom (DoF) are constrained by the demands of dedicating a motor to each joint, and while mechanical multiplexing reduces actuator count, existing clutch designs are bulky, force-limited, or restricted to one output at a time. The problem addressed in this study is how to achieve high-force, multiplexing that supports both simultaneous and sequential control from a single motor. Here we show an electrostatic capstan clutch-based transmission that enables both single-input-single-output (SISO) and single-input-multiple-output (SIMO) multiplexing. We demonstrated these on a four-DoF tendon-driven robotic hand where a single motor achieved output forces up to 212 N, increased vertical grip strength by 4.09 times, and raised horizontal carrying capacity by 354\% over manufacturer specifications. These results demonstrate that electrostatic multiplexing provides versatile actuation, overcoming the limitations of prior systems.

Figures (9)

• Figure 1: In this work, we show how our novel multiplexing architecture enables a single motor to: A) Increase horizontal holding capacity 354% to 111.2 N, compared to the robot hand manufacture's specified capability. B) Increase vertical grip strength over traditional architectures by up to a factor of 4.09 to 22.2 N with SISO multiplexing. C) Demonstrate the functionality of our system by using SIMO multiplexing to grasp a drill, SISO multiplexing to increase vertical grip strength from 55.1 N to 118.76 N, and to actuate a modified trigger.
• Figure 2: Implementation of electrostatic capstan clutch described in Amish-2024-JRCC. A stainless steel band is wrapped around a conductive input shaft with a layer of PBI (labeled "dielectric"). When a voltage is applied between the clutch electrode and input shaft, the clutch electrode electrostatically adheres to the input shaft and rotates along with it. Input voltage was limited to 1000 V to avoid dielectric breakdown at 1200 V. The measured maximum static holding torque before the clutch would slip was 1.84 N·m (144.9 N holding force) and consumes 2.4 mW.
• Figure 3: Implementation of a single unit controlling one DoF of a slider capable of rightward translation, leftward translation and holding position. A single motor continuously rotates one input shaft CW and counter rotates the second input shaft through a gear. When the right translation clutch is engaged, it couples the CCW rotating shaft to rotate the leadscrew clockwise, causing a rightward translation. The left translation clutch couples the leadscrew to the CW rotating clutch, resulting in leftward translation. The leadscrew is not backdrivable and maintains position when neither clutch is engaged.
• Figure 4: The full multiplexer is comprised of four single units to separately control four outputs, depicted in Fig. \ref{['fig:single-unit']}, tiled in parallel and sharing the same input shafts. Two clutches operate a single lead screw. By clutching to the bottom input shaft, the output slider will be actuated to the right. Engaging the top clutch will cause a leftward translation. When neither clutch is activated, position is maintained as the leadscrew is non-backdrivable.
• Figure 5: In SISO operation, a single motor is clutched to different outputs, each individually in time. The top circles indicate which output is selected. As clutches are individually activated, the corresponding 2.27 kg weight is lifted 50 mm. The average output power for lifting the weight between all outputs was 0.77 W. The multiplexer transmission efficiencies for each output is recorded in table \ref{['tab:SISO-Eff']}.