In this paper, we present the design of a low-cost haptic actuator called a pactor that is capable of delivering tactile stimuli eliciting varying levels of attention capture. The pactor design consists of a crankshaft mechanism attached to an RC servo that produces a linear displacement at the endpoint. It can apply a 0–2.0cm displacement to the human body at a variety of actuation rates. We conducted a study to measure the displacement detection threshold for the pactors, and their perceived level of attention capture and urgency. In our study with 25 participants we found that actuation speed was the most significant factor affecting detection threshold. We also observed that the level of attention capture was dependent on both actuation speed and stimulus intensity. We propose that dynamic range of actuation speed and stimulus magnitude are important design parameters that enable actuators to achieve variable attention capture (VAC). This in turn will allow actuators to provide better opportunities to present information at an appropriate level of attentional salience.

The design of a partial weight-bearing compliance aid for orthopedic surgery patients is presented in this paper. This device is capable of detecting weight-bearing loads and delivers appropriate vibrotactile haptic stimuli to the user to encourage compliance with partial weight-bearing orders. This is achieved with either haptic confirmations of correct weight-bearing loads or haptic alerts when loads exceed a prescribed limit. In a preliminary evaluation with 9 healthy subjects, it was demonstrated that the device has a dynamic sensing accuracy of ±2.43kg (±5.34 lbs.) within the 2.3-23kg (5-50 lb.) weight-bearing range, which is within the clinical tolerance for partial weight bearing. Additionally, a user wearing this device was able to detect the haptic stimuli and discern whether he was exceeding the weight-bearing load. Ultimately the goal is to create a low-cost alternative to existing products seeking to improve patient weight-bearing compliance, with viability as a take-home rehabilitation aid.

The dynamic behavior of an inverted pendulum platform inherently reveals information about its interaction with the environment. The closed loop controller puts the unstable plant into dynamic equilibrium, where very small external forces result in persistent excitation of the system. Our previous work has shown that we are able to detect and estimate external forces on an inverted pendulum base using only dynamic state information from the controller. The Yale Inverted Pendulum Door Opening Robot (YIPDOR) has gained a simple 4 degree of freedom (DOF) arm with the goal of opening and traversing doorways with both heavy and sprung doors. We have explicitly omitted dedicated force sensors. Estimation methods using only the Jacobian and joint torques do not provide adequate estimates of external forces on this system. While improved force estimation continues to be a goal for the project, we propose that traversal of sprung doors may be accomplished with low-level, dynamic postures and detection of changes in dynamics rather than explicit force estimation and control. Changes in the equations of motion and dynamic constraints (contact, unlatching, door movement) are detected by using filtered derivatives of relevant parameters. This feature extraction research increases the safety and performance of the balancing and manipulation system without any additional dedicated sensors.

In this paper a method for force estimation on inverted pendulum type balancing platforms is presented and examined. Inverted pendulum systems are sensitive to small external forces because they are being balanced about an unstable position of zero force. The perturbations that result from external forces cause noticeable changes to the system state variables and it is these changes that are used to estimate the force. We present a dynamic model for the inverted pendulum and then examine several methods for estimating an external force. Use of the open loop plant parameters offers the best method for estimating the net torques acting on the system. A significant outcome is that estimation can be performed using only the system mass properties along with the inertial and displacement sensors that are required for balancing and this estimate is more accurate than a comparable drive system in a statically stable robot. Thus improved one axis force estimation may be accomplished using the same sensors that are used to stabilize the platform.

This paper discusses the design of the control algorithm used to control a two-wheeled balancing transporter. The device is a drive and steer by wire device using closed loop feedback to provide both fore-aft stability as well as directional control. The controller consists of two parts, a closed loop pitch controller that maintains balance and governs the morion of the device forward and backward and a yaw or steering controller that governs the turn rate via differential wheel speed. The transporter is unique in that it is much smaller than the operator and it couples to motions of the entire body, rather than an arm or leg independently. An impedance model was adopted to account for the human in the loop, there by making the design problem tractable and relatively straightforward to implement.

Current force control capabilities are limited by actuator performance. Brush friction and actuator saturation lead to limit cycles and instability in many force control systems. The authors propose that actuators with the proper passive characteristics provide the best potential for fast, accurate force control. The authors report on a new actuator concept which combines two actuators to create a micro-macro actuator which has improved force resolution and bandwidth. Unlike previous micro-macro robots which used actuators coupled in series, the actuators in this system are coupled in parallel using a compliant transmission. Three specifications for force control performance are defined and a model is presented. A control law for the combined actuator is presented and a general analysis of the design is formulated. Finally, measurements of performance in a prototype device are presented. This system has achieved force resolution of 0.25% and force control bandwidth of 60 Hz.