Publications

Haptic gloves require actuators capable of precise force trajectory tracking. Pneumatic actuators exhibit high force to weight ratio performance; however, their usage is often limited by high nonlinearities and friction-induced uncertainties. This study investigates the position and pressure-dependent static friction in small-scale pneumatic actuators. A new stiction model is proposed that explicitly incorporates these dependencies to accurately characterize static friction effects. In order to exploit this model, a sliding mode controller (SMC) with estimated friction compensation is developed and experimentally validated. When actuator force is estimated using pressure measurements, results show that incorporating the friction model significantly reduces amplitude errors compared to uncompensated control.

This paper presents the mechanical design and kinematic analysis of SMU Haptic Glove, which incorporates seven degrees of freedom (DOF) that are pneumatically actuated and developed for 3D elastographic imaging virtual palpation. This paper outlines the mechanical design of the SMU Haptic Glove The two-dimensional workspace for each finger and the glove’s three-dimensional workspace are determined from the actuator positions using closed-form expressions based on the design geometry and are measured using embedded linear sensors.

Pneumatic actuators exhibit strong nonlinearities and considerable uncertainties that include time-varying friction, making precise force tracking control challenging. This is exacerbated in small-scale cylinders, where internal friction can represent a significant percentage of the maximum output force. To address these issues, this paper presents an adaptive sliding mode control method with friction compensation (ASMC-FC). The controller integrates online parameter adaptation for managing slow-varying friction uncertainties with sliding mode control (SMC) to ensure robustness against unmodeled dynamics and rapidly changing uncertain parameters. Experimental validation is conducted on a double-acting, single-rod small pneumatic cylinder. The results demonstrate that the proposed approach offers better force tracking and increased robustness compared to standard SMC.

This paper presents a novel approach to studying bipedal locomotion using magnetically actuated miniature robots. Traditional bipedal locomotion machines are expensive and complex. In contrast, we introduce “Big Foot”, a lightweight 0.3 g robot designed to explore fundamental concepts of bipedal locomotion without requiring complex hardware.

Static friction, also known as stiction, is a primary source of tracking error in pneumatic cylinders, which significantly limits their use in high-precision force control tasks. This paper presents a detailed experimental study of the static friction behavior of a small pneumatic cylinder, examining how the friction force depends on piston position and supply pressure. Based on these findings, a new static friction model that considers pressure and position is developed to accurately represent the stiction phenomenon. Additionally, a Sliding Mode Controller (SMC) is designed and implemented to produce a desired output force. The SMC’s performance is evaluated experimentally both with and without the proposed friction compensation model. Results show that the SMC with the integrated compensation reduces steady-state force tracking errors compared to the uncompensated controller.

This paper presents an analysis of the precision of fingertip location for a 7 degrees of freedom (DOF) pneumatic haptic glove developed at SMU for 3D elastographic imaging virtual palpation.The 2D workspace for each finger and the 3D workspace for the glove are calculated from the actuator positions using closed-form expressions based on design geometry. The fingertip locations are measured using a 5-camera OptiTrack motion capture, and the results are compared with the fingertip positions obtained using the linear sensors integrated in the design of each finger joint.This work is an essential step in the development of a virtual palpation system of 3D elastographic medical images.