DC Motor Damping: A Strategy to Increase Passive Stiffness of Haptic Devices
10 Jun 2008-pp 53-62
TL;DR: A configuration of the H-bridge is employed which can cause physically dissipative damping to impart stability to the haptic device, which results in an increase in passive wall stiffness over the performance of an undamped DC motor.
Abstract: Physically dissipative damping can increase the range of passive stiffness that can be rendered by a haptic device. Unlike simulated damping it does not introduce noise into the haptic control system. A DC motor can generate such damping if it's terminals are shorted. We employ a configuration of the H-bridge which can cause this damping to impart stability to our haptic device. This results in an increase in passive wall stiffness of about 33.3% at a sampling rate of 100Hz and 16.6% at 1kHz over the performance of an undamped DC motor. We have also attempted to implement the system on the hybrid haptic control system [1], it was seen that a perceivable change in the performance of this system was not observed by the use of DC motor damping.
Citations
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11 Jul 2012
TL;DR: In this paper, an actuator that is capable of simultaneous and independent physical damping and stiffness modulation is presented, using optimal control techniques, and several numerical simulation results are presented, in addition to an experiment realised on variable impedance robotic hardware.
Abstract: Until now, design of variable physical impedance actuators (VIAs) has been limited mainly to realising variable stiffness while other components of impedance shaping, such as damping, are either fixed (e.g., with the addition of fixed passive dampers) or modulated with active feedback control schemes. In this work we introduce an actuator that is capable of simultaneous and independent physical damping and stiffness modulation. Using optimal control techniques, we explore how variable physical damping can be exploited in such an actuator in the context of rapid movement. Several numerical simulation results are presented, in addition to an experiment realised on variable impedance robotic hardware.
49 citations
Cites methods from "DC Motor Damping: A Strategy to Inc..."
...In previous work the same effect has been used in the context of designing adjustable dampers in haptic interfaces [19], [20]....
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TL;DR: A new concept of passivation method to increase the dynamic range of impedance in which a haptic interface can passively interact and shows better performance than the recently proposed field-programmable gate array-based time-domain passivity approach.
Abstract: Inspired from the graphical interpretation of passivity in a position versus force xy graph, this paper proposes a new concept of passivation method to increase the dynamic range of impedance in which a haptic interface can passively interact. The position versus force graph represents the energy behavior in a one-port haptic interface while the haptic interface is traveling in (pressed) or out of (released) a virtual environment (VE). It interprets that to make the one-port system passive, it is sufficient to bound the releasing path below the pressing path in the position versus force graph. To realize the bound, the computed force output from the VE is saved into a designated memory, addressed by current position, while the haptic interface is pressed. Thereafter, the saved force can be reused to upper-bound the releasing path below the saved pressing path while the haptic interface is released. The proposed method is generalized from preliminary work by including interaction with a moving virtual object and multi-DOF extension, together with more systematic and detailed explanations about the methods. In particular, we reconfigure the one-port moving virtual object as a two-port haptic controller and a connected one-port moving inertia. This reconfiguration allows implementation of the preliminary approach including the interaction with moving virtual objects by using an error versus force passivity instead of a position versus force passivity. This two-port extension also allows generalization of the proposed method to multi-DOF interactions by introducing virtual proxy as a virtual moving object. The proposed method is tested with a single and a multi-DOF haptic interface and shows better performance than the recently proposed field-programmable gate array-based time-domain passivity approach .
31 citations
Journal Article•
TL;DR: In this article, Behensky and Milliken used mechanica l actuators to apply forces to the user by simulating the physics of the user's virtual world and sending them to the actuators so that the user can feel them.
Abstract: Force display technology works by using mechanica l actuators to apply forces to the user, By simulating th e physics of the user's virtual world, we compute these forces in real-time, then send them to the actuators so that the user feels them, The force display technology we use in th e Sandpaper system is a motor-driven two-degree of freedo m joystick (built by Max Behensky and Doug Milliken) . The joystick position is reported to the software, whic h computes the appropriate forces for the joystick's motors .
17 citations
TL;DR: A dual-rate sampling scheme in which the position and velocity loops of a haptics controller are decoupled and sampled at different rates is proposed, which enables independent sampling of the position data at higher rates, while simultaneously sampling the velocity data at appropriate rates.
Abstract: Conventional controllers in impedance-based haptic interfaces are sampled data systems that utilize position and velocity information for the necessary force feedback. In a canonical virtual wall simulation, this feedback force is generated based on interaction with the wall simulating certain stiffness and damping. Increasing the sampling rate of the controller increases the stable range of virtual wall stiffness. However, an increased sampling rate exacerbates the velocity information, decreasing the stable range of virtual wall damping. In this work, the authors propose a dual-rate sampling scheme in which the position and velocity loops of a haptics controller are decoupled and sampled at different rates. The scheme enables independent sampling of the position data at higher rates, while simultaneously sampling the velocity data at appropriate rates. In this paper, the authors provide experimental and theoretical implications of the effect of dual-rate sampling on the stability of a haptic interface. Experiments with a single degree-of-freedom (DOF) haptic interface reveals an enhanced region of stable virtual wall stiffness for a particular range of virtual wall damping, compared to the values with conventional uniform-rate scheme. Virtual wall stiffness ranging from 150 - 360 Nm/rad was stably implemented over a range of 0 - 1 Nms/rad of virtual wall damping using the proposed scheme at position loop sampling rate of 20kHz and velocity loop sampling rate of 2kHz. Whereas in the conventional scheme, the stable range of virtual stiffness dropped considerably (∼ 0 Nm/rad) for the virtual wall damping above 0.1 Nms/rad when the uniform rate sampling of 20kHz was used for both the position and velocity sampling loops. Theoretical stability analyzes using classical control tools and simulations justified the effectiveness of the proposed scheme. The scheme is easy to implement and extensible to multi-DOF haptic interfaces as well.
13 citations
TL;DR: A dual-rate sampling scheme is proposed here for conventional controllers, whereby the position and velocity loop is sampled at different rates, and experimental results demonstrate the effectiveness of proposed scheme, particularly at higher sampling rates.
Abstract: Conventional controllers used in haptic devices are sampled data systems in which the position and velocity of the device is required to realize a visco-elastic virtual wall interaction. Increasing the sampling rate of the controller improves the stable range of virtual wall stiffness but simultaneously exacerbates the estimated velocity. This inefficient velocity estimation limits the implementation range of virtual damping at higher sampling rates, thereby reducing the dynamic range of stable impedance or Z-width of the haptics controller. A dual-rate sampling scheme is proposed here for such controllers, whereby the position and velocity loop is sampled at different rates. Implications of the proposed scheme on the Z-width of haptics controller using a 1-DOF (Degree-of-Freedom) custom haptic device is discussed. Experimental results demonstrate the effectiveness of proposed scheme, particularly at higher sampling rates.
12 citations
References
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13 Sep 2001
TL;DR: A patent-pending, energy-based method is presented for controlling a haptic interface system to ensure stable contact under a wide variety of operating conditions and requires very little additional computation and does not require a dynamical model to be identified.
Abstract: A patent-pending, energy-based method is presented for controlling a haptic interface system to ensure stable contact under a wide variety of operating conditions. System stability is analyzed in terms of the time-domain definition of passivity. We define a "passivity observer" (PO) which measures energy flow in and out of one or more subsystems in real-time software. Active behavior is indicated by a negative value of the PO at any time. We also define the "passivity controller" (PC), an adaptive dissipative element which, at each time sample, absorbs exactly the net energy output (if any) measured by the PO. The method is tested with simulation and implementation in the Excalibur haptic interface system. Totally stable operation was achieved under conditions such as stiffness >100 N/mm or time delays of 15 ms. The PO/PC method requires very little additional computation and does not require a dynamical model to be identified.
744 citations
"DC Motor Damping: A Strategy to Inc..." refers methods in this paper
...Hannaford et al., [ 9 ] present a “Passivity Observer” and “Passivity Controller” method to track energy movements in haptic interactions with the user and to dissipate the excess energy if it tends to cause active behavior in the system....
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08 May 1994
TL;DR: This paper addresses the performance of force-reflecting interfaces and suggests that an important measure of performance is the dynamic range of achievable impedances-"Z-Width"-and that an impedance is achievable if it satisfies a robustness property such as passivity.
Abstract: This paper addresses the performance of force-reflecting interfaces ("haptic displays"). The authors suggest that an important measure of performance is the dynamic range of achievable impedances-"Z-Width"-and that an impedance is achievable if it satisfies a robustness property such as passivity. Several factors affecting Z-Width-sample-and-hold, inherent interface dynamics, displacement sensor quantization, and velocity filtering-are discussed. A set of experiments designed to evaluate these factors is described and experimental results are presented. A striking result is that inherent interface damping exerts an overwhelming influence on Z-Width. >
709 citations
"DC Motor Damping: A Strategy to Inc..." refers background in this paper
...This line of reasoning has been described in [2]....
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...Therefore damping can contribute to stability only if it is implemented as a controlled physically dissipative process [2]....
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01 Feb 1990
TL;DR: The force display technology used in the Sandpaper system is a motor-driven two-degree of freedo m joystick, which computes the appropriate forces for the joystick's motors in real-time.
546 citations
"DC Motor Damping: A Strategy to Inc..." refers background in this paper
...Minsky et al.,[ 3 ] investigated the stability of Haptic interaction and derived a condition for the stability of the haptic device based on considerations of sampling rate of the controller....
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18 Sep 1993
TL;DR: A theoretical analysis of the implementation of stiff wall implementation is presented and the main result is a criterion for the passivity of a virtual wall in terms of two nondimensional parameters.
Abstract: The performance of a haptic interface is often reported in terms of the dynamic range of impedances it may represent. At the low end, the range is typically limited by inherent dynamics of the interface device, such as inertia and friction. At the high end, the range is typically limited by system stability. In a number of the applications, the principal limitation has proven to be the achievable upper limit on impedance. Therefore, a benchmark problem of considerable importance is the implementation of a stiff "wall". Contacting a wall may be described as the reversible transition from a region of very low impedance to one of very high impedance. A theoretical analysis (supplemented with discussion of experimental and simulation results) of stiff wall implementation is presented. The main result is a criterion for the passivity of a virtual wall in terms of two nondimensional parameters. >
371 citations
"DC Motor Damping: A Strategy to Inc..." refers background in this paper
..., [7] presented a theoretical analysis of the passivity of the stiff wall and in 2004, Miller et....
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TL;DR: A study of this problem, which relates the maximum achievable object stiffness to the elements of the control loop, examines how the sampling rate, quantization, computational delay, and amplifier dynamics interact with the inertia, natural viscous, and Coulomb damping of the haptic device.
Abstract: Rendering stiff virtual objects remains a core challenge in the field of haptics. A study of this problem is presented, which relates the maximum achievable object stiffness to the elements of the control loop. In particular, we examine how the sampling rate, quantization, computational delay, and amplifier dynamics interact with the inertia, natural viscous, and Coulomb damping of the haptic device. Nonlinear effects create distinct stability regions, and many common devices operate stably, yet in violation of passivity criteria. An energy-based approach provides theoretical insights, supported by simulations, experimental data, and a describing function analysis. The presented results subsume previously known stability conditions
295 citations