Actuators that interact with the environment and humans require a variable reduction ratio to maintain high motor efficiency over various output loads. Actively controlled continuous variable transmission optimizes motor efficiency by changing the gear ratios at the desired time. This study presents the modeling, design, and characterization of a transmission capable of actively controlling the reduction ratio for robotic applications. Power transmission through the proposed compression mechanism using a compression spring without an external energy source enabled a compact design. The transmission ratio range (1:1 and 4.2:1) is determined through kinematic analysis of the toroidal drive design. The reduction ratio shifting module enabled a low power consumption during shifting (approximately 3.5 W) and static condition (approximately 0.2 W) through the nonbackdrivability and self-locking features of the worm gear. The characterization results showed good power transmission efficiency of 75% across the entire operating range. The system was equipped with overload protection features for slipping between the disk and roller, exhibiting a torque capacity of 2.4 N·m. Finally, we compare the performance of our proposed variable transmission with that of the existing system to demonstrate the applicability of our design to robot actuators.

Tactile sensing can enhance robotic grasping by providing contact information unavailable from vision or control signals alone. However, implementing tactile sensing in robotic hands is often constrained by external wiring, data-acquisition hardware, power requirements, and limited fingertip space. This study presents a self-contained capacitive tactile fingertip module for adding wireless multi-point contact sensing to robotic grippers. The module integrates a 3 × 1 array of thin flexible capacitive sensors, a capacitance-to-digital converter, a Bluetooth-enabled microcontroller, and an onboard battery within a compact fingertip-shaped housing. It can be mounted in place of an existing fingertip and operates independently of the robotic hand controller. Individual sensors characterized before module integration responded near-linearly to normal compression up to 2.5 N, with an approximately 8% relative capacitance change at 2.5 N and R² = 0.99, and were evaluated over 100 repeated compression cycles. In proof-of-concept grasping tests with an empty PET bottle, a water-filled PET bottle, and a water-filled aluminum tumbler, the assembled module produced distinguishable capacitance changes at the mid- and proximal-position sensors, providing relative information on contact location and local loading rather than calibrated force. These results demonstrate the feasibility of wireless tactile sensing in robotic grasping using a compact standalone fingertip module.

Actuators that interact with the environment and/or humans require a variable reduction ratio to maintain high motor efficiency over a wide range of output loads. Actively controlled continuous variable transmission (CVT) allows the motor to operate with high efficiency. Most CVT designs have a complex shifting controller design and need high power for gear shifting. Spherical CVTs have simplified the shifting controller design, desirable for mobile robot applications. However, this design lacks torque capacity and is inefficient beyond a certain gear ratio. This study presents the modeling, design, and characterization of a transmission capable of actively controlling the reduction ratio. Power transmission through the proposed compression mechanism using a compression spring without an external energy source enabled a compact design. A wide range of transmission ratio (~ 4.2:1) based on kinematic analysis of the toroidal drive design. The reduction ratio shifting module enabled a low power consumption during shifting (< 3.5 W) and static condition (~ 0.2 W) through the non-backdrivability and self-locking features of the worm gear. The characterization results showed good power transmission efficiency of over 75% across the entire operating range. The system also exhibited a torque capacity of 2.4 Nm. It is equipped with overload protection features for slip between the disk and roller. Finally, we compare the performance of our proposed variable transmission with that of the existing system to demonstrate the applicability of our design.

This article presents a design framework for a backdrivable, bi-directionally energy-efficient 3K compound gearbox with a high reduction ratio and low backlash. The 3K compound planetary gearbox is a promising candidate for the robot actuators deployed in physically interacting environments possessing a compact design with a high gear ratio and high back-drivability. However, the existing 3k composite planetary gearbox has a high backlash for use in robot actuators. In this context, the proposed design framework comprises 1) backlash modeling 2) effective inertia of the 3K compound planetary gearbox 3) maximization of the bi-directional efficiency under bounded backlash constraints. We created a prototype to demonstrate the design framework for a low-backlash gearbox with a high reduction ratio (1/96.2) which is both bi-directionally efficient and back-drivable. The angular backlash of the prototype was 7.1 arcminutes. The forward and backward efficiencies of the developed prototype were 87.1 % and 82.5 %, respectively, and the back-driving starting torque was 0.025 Nm.