Proposed Torque Sensor Research Articles

Design and Hysteresis Modeling of a Miniaturized Elastomer-Based Clutched Torque Sensor

Elastic torque sensors have been widely used for small-scale robots such as hand exoskeletons to achieve torque control. However, designing a miniaturized and lightweight elastic torque sensor with human–machine interaction safety is still a challenge. In this article, a novel miniaturized and lightweight elastomer-based clutched torque sensor is presented. A rubber spring is designed and used to reduce its volume and weight. A wafer disk clutch is devised to improve mechanical safety. The torque sensor is 29.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times18$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times24$ </tex-math></inline-formula> mm in dimension and weighs 23 g. Compared with the state-of-the-art elastic torque sensors for hand exoskeletons, the volume-to-torque ratio is reduced by 15.48%, and its weight is reduced by 23.33%. Since the hysteresis characteristics of the rubber spring leads to a nonlinear deformation–torque relationship, an improved parametric Gaussian process regression (PGPR) method based on the nonlinear autoregressive moving average structure with exogenous inputs (NARMAX) is proposed. A combined kernel function for the improved PGPR is designed to improve the fitting performance. Finally, experiments have been conducted to verify the mechanical safety and torque sensing performance. The force caused by collision on the proposed torque sensor is less than that on the torque sensor without the clutch (reduced by 51.78%). The proposed hysteresis model can reduce the maximum absolute modeling error to 7% compared with those of other intelligent hysteresis models (the modeling error is 12.32%). Therefore, the experimental results indicate that the proposed torque sensor can improve the mechanical safety and achieve accurate torque sensing.

Development and Application of Motor-Equipped Reaction Torque Sensor with Adjustable Measurement Range and Sensitivity

Various high-performance force/torque sensors have been developed for the purpose of advancing automation systems. However, the demand for simple torque measurement of rotating shafts continues to exist, and expensive multi-axis sensors need not be wasted here. In this paper we propose a simple motor-equipped single-axis reaction torque sensor to measure the applied torque continuously using a load cell. The proposed sensor has long lever and base linkages, and the adjustable moment arm consequently enables adjusting measurement range and sensitivity by repositioning the assembled load cell on the two linkages. This paper shows the design of the proposed torque sensor, and it is evaluated by experiments for various applied torque and lever length. Moreover, the sensor is applied to an existing example: a commercial balanced-arm lamp with and without its balancing spring. The proposed torque sensor can continuously and successfully measure the applied torque, and it will be utilized in various industries and laboratories without much money.

Lightweight Torque Sensor Based on a Gradient Grating Period Guided-Mode Resonance Filter

This paper describes the design, fabrication, and testing of a lightweight and compact torque sensor system based on a gradient grating period guided-mode resonance (GGP-GMR) filter and a flexure–elastic-force-sensing element. The GMR filter exhibits a characteristic resonant reflection, when illuminated with a broadband light source at normal incidence. Instead of a fixed grating period, the GGP-GMR filter consists of grating periods varying from 250 to 550 nm with an increment of 2 nm. Given the flexibility of the plastic-based GGP-GMR filter, it can be bent conform to the cylindrical surface of the flexure. The applied torque induced deformation of the flexure and angular displacement of the attached GGP-GMR. For a stationary light source, the angular displacement of the GGP-GMR filter results in illumination at different locations (grating periods), leading to a shift of the resonant reflection wavelength. The magnitude of shift in the reflection wavelength can be correlated to the magnitude of deformation and the applied torque. In addition, commercial software based on the finite element method was used to simulate the proposed design, which indicates that the flexure made of medium-carbon steel can withstand the torque of 35 Nm without yielding. Furthermore, the simulation results (torque-induced deformation) were consistent with those obtained using the proposed torque sensor system. Torque measurements from 0 to 25 Nm showed good linearity. The limit of detection achieved was 0.77 Nm.

A low cost 3D-printed robot joint torque sensor

Technological advances allow researchers to develop advanced arm robots and can safely work side by side with humans Therefore, a robot arm controller can be designed in such way that the robot arm can move along the desired trajectories and act upon external influences, in this last case, the torque sensor plays an important rule. Currently torque sensors are available in the market has a high price. In this work, an inexpensive robot joint torque sensor is presented. Most parts of this sensor are made using 3D printers. While the other components are easily can be found in the market and with a relatively low-costs. The development of this sensor is intended to facilitate the prototyping of the robot arm for educational and research purposes. The basic idea of the sensor mechanism is to convert torque into a force absorbed by a spring. Then, the encoder senses the direction and the value of the input torque. This torque sensor can be easily too customized. Thus this sensor can be tailored to the needs by replacing some parts such as encoder and spring. The mechanism of this sensor can also be adjusted with the actuator to be paired. Experiments have been conducted to verify the accuracy and the performance of the proposed torque sensor.

Digital High-Resolution Torque Sensor and Signal Processing

A contactless thin-layered torque sensor with fully digital signal processing circuit is proposed in this paper. The mechanical structure of the torque sensor is an orange-slice-alike flexible body. Two links with black/white stripes are aligned beforehand as no any torque applied to the shaft. The two links play the role of optical grating by resolution. As long as the orange-slice-alike flexible body, sandwiched by the aforesaid links, is subject to an external torque applied, a twisted angle is induced between the two thin photograting discs. Two sets of photodetector cooperate with the two discs with optical gratings to generate two pulse sequences. Therefore, a time delay between these two pulse sequences can be acquired as long as the shaft is twisted by a torque. A counter IC is employed to quantify this time delay in terms of the torque applied, and the time period in terms of rotational speed of shaft. One of the merits of the proposed torque sensor is that real-time measurement on torque applied becomes feasible even if the shaft, subject to external torque, is rotating at high speed. Other advantages of the fully digital signal processing circuit include: 1) no need to conduct analog/digital conversion and 2) free of noise, crosstalk and electromagnetic interference.

Design of joint torque sensor with reduced torque ripple for a robot manipulator

Joint torque sensors are widely used in service robots for force control and collision detection. However, commercial torque sensors and amplifiers are too bulky to install inside robots. In this study, we propose an amplifier-embedded torque sensor because placing the amplifier away from the sensor tends to add noise to the output signal. Furthermore, joint torque sensors experience the torque ripple generated by the harmonic drive gear. Therefore, a torque ripple reduction method is also proposed in this study. FEM analysis was conducted to improve the sensitivity of the torque sensor to only torques in the direction of joint rotation. To avoid external noise and excessive wiring, an embedded amplifier, which can be installed inside the joint of the robot arm with the torque sensor, was developed. Also, the torque ripple reduction method based on the change in the installation position of Wheatstone bridges was developed. Through various experiments, the performance of the proposed torque sensor was verified.