Yo-An Lim

A Survey of Haptic Control Technology

Haptics technology allows one to interact with virtual environments, augmented environments, and real environments providing tactual sensory information. Science and technology of haptics can in general be classified into three groups: machine haptics, computer haptics, and human haptics. This paper surveys the state-of-the-art of haptic control technology for virtual environments and teleoperation (real environments) and then proposes possible future research directions in the following areas: haptic stability control, bilateral teleoperation control, and stability enhancement control.

Teleoperation of a multi-purpose robot over the internet using augmented reality

Bilateral teleoperation using augmented reality is proposed for a multi-purpose robot called SpiderBot-II that is an indoor-installed wire-driven parallel manipulator. It is intended to be used for various applications, including in-house rehabilitation training and daily life assistance such as walking assistance and health monitoring, especially for the elderly or the handicapped that spends most of time at home. Through the teleoperation over the Internet, a therapist or an attendant in a remote site can give help to the physically disabled by directly manipulating the robot. For easy recognition of the obstacle, predefined markers are attached to each obstacle in the workspace. For better teleoperation, moreover, reaction force between obstacles and the end-effector, which is calculated using force field, is given to a remote operator and this enables the operator to perform the teleoperation more effectively. Force field, which is proportional to proximity between obstacles and the end-effector, is generated to facilitate the obstacle avoidance and visually augmented on the operators screen for better recognition of obstacles.

A Wearable 3-DOF Wire-driven Force Feedback Device

This paper addresses a new design and control of a wearable 3DOF force feedback device based on wire-driven parallel mechanisms. Unlike the existing wearable force feedback devices, the proposed wire-driven device is not supported by a rigid frame attached to the upper body. All electrical components of the device are located inside a wearable jacket and the device is powered by a few batteries. The force applied to the end-effector is produced by the tension of three wires connected to it and the tension of the wires are controlled by three motors. The kinematics and workspace analysis are discussed and a simple algorithm that makes a wire maintain minimum tension while without making it slack is proposed. Also end-effector position errors caused by the flexible positions of wire extracting points are discussed. Finally, some empirical results are presented. This device may be used in some applications which need force feedback functions, especially with mobile computer devices such as mobile phones, computers and PDAs

Active synchronized motion control for comfortable walking support

The safety and comfort of user are the two important requirements that a service robot must fulfill to qualify as assistive device for elderly persons. Unlike scenarios of manipulation assistance, human user is physically attached with the robot in those of walking/mobility assistance. Any force/torque generated at the robot (end-effector) is transferred to human body that causes the discomfort and safety problem for the user. If the motion of robot system is made synchronized with human users movement during walking, it can be more comfortable for elderly user. This paper proposes a new control strategy for synchronized movement of walking support system with the human users walking. For this strategy, the average step size of a particular user is obtained through initial short test and the direction of motion is guided online by human user. Proposed scheme is implemented on SpiderBot-II, a wire-driven parallel mechanism, conceptualized for assisting elderly persons. Users comfort is assessed through measurement of link reaction forces during walking assistance. The rationale behind such scheme is the common assistance scenario during walking. The human assistant synchronizes his walking pattern and speed with that of elderly user to make it more comfortable for the latter. Preliminary experimental results show that this control scheme is capable of realizing a comfortable walking assistance for elderly persons.

A novel planar walking algorithm for virtual walking machine

This paper proposes a novel planar walking algorithm for the Virtual Walking Machine (VWM), which is a dual foot platform type locomotion interface. Unlike existing algorithms used for VWM, the proposed algorithm utilizes a constraint relationship between two platforms as well as position control. Experiments on the VWM show that the proposed planar walking algorithm can generate straight and turning motions which are smoother and collision-free.

Performance of equivalent frequency-dependent damping

An analog input shaper (AIS) was proposed as a means for increasing the virtual impedance range that could be stably displayed by haptic interfaces. The AIS reduces high frequency inputs to haptic interfaces, since high frequency inputs that usually occur during collisions with very stiff virtual objects can induce instabilities. The AIS is composed of an analog high-pass filter, two half-wave rectifiers, and an adder. In this paper, we show analytically that how the AIS works as equivalent frequency-dependent damping. In addition, we present both the numerical simulation results and the virtual wall experiment results using a custom-built 1-DOF haptic interface and show that the AIS can significantly increase the Z-Width.

A Smooth Planar Walking Algorithm for Virtual Walking Machine (K-Walker)

This paper proposes a novel planar walking algorithm for the virtual walking machine that is a dual foot platform type locomotion interface. Unlike existing algorithms, the proposed algorithm utilizes a constraint relationship between two platforms as well as position control. Experiments on the VWM show that the proposed planar walking algorithm can generate straight and turning motions which are smoother, collision-free

A Digital Input Shaper for Stable and Transparent Haptic Interaction

This paper presents frequency-dependent digital damping referred to a digital input shaper (DIS). Compared to the previously proposed analog input shaper, the DIS makes the implementation of damping much more flexible and significantly reduces the electrical noise. Moreover, the DIS incorporates a position control method at the initial contact to improve the perceived contact hardness. Then, through a series of simulations and benchmark virtual wall experiments, we show that the DIS can significantly increase the impedance range that a haptic interface can stably display and that the initial contact hardness that a user perceives can be noticeably improved by using the proposed position control method. Finally, the DIS is applied to scaled teleoperation using an atomic force microscope and through contact experiments it is shown that it can indeed increase the scaled impedance of a real environment that can be stably displayed. ©

Stability enhancement of haptic interaction by analog input shaper and its application to scaled teleoperation

This paper addresses an analog input shaper introduced in haptic control to improve the stability when interacting with virtual environments. High frequency inputs to a haptic device, which can occur in collision with a virtual wall with high stiffness, can bring limit cycle oscillations and instabilities. In order to reduce the high frequency input to an haptic device an analog input shaper is added to the control system. Since the input shaper acts as a low-pass filter, when a haptic pointer leaves the virtual wall with high stiffness, a user may feel slow decrease of impedance, moreover there may be negative impedance as if the wall is pulling. In order to prevent this, we add half-wave rectifiers which allow fast decrease of impedance and no negative input to a haptic device. The input shaper reduces the total energy supplied to a haptic device by preventing inputs with high frequency from flowing into a haptic device. Therefore it can be regarded as an artificial damping element. In order to apply the Energy-Bounding Algorithm (EBA),1 which can guarantee the stable haptic interaction, to a scaled teleoperation in a virtual nano-environment two scaling factors (velocity and force) are incorporated into EBA. By applying the analog input shaper to EBA in scaled teleoperation, the range of virtual wall stiffness which can be stably rendered by a haptic device is significantly extended.

Stability enhancement of haptic interaction by frequency-dependent damping and its application to scaled teleoperation

This paper presents a frequency-dependent damping element, called an analog input shaper (AIS), to improve the stability of haptic interaction with virtual or real environments. High frequency inputs to a haptic interface, which usually occur in the collision with very stiff objects, can bring limit cycle oscillations and instabilities. In order to reduce these high frequency inputs and thus to improve the stability of haptic interaction, the AIS is added to the haptic system. Moreover, the AIS is applied to a passivity-based haptic stability control algorithm, called an energy-bounding algorithm (EBA), to increase the displayed impedance range by the EBA. Through scaled teleoperation experiments using an atomic force microscope (AFM), we show that the AIS can enhance stability during haptic interaction and consequently increase impedance range that a haptic interface can stably display. Also, we show that the AIS can alleviate conservativeness of the passivity-based haptic control algorithms.