Realizing low-impedance rendering in admittance-type haptic interfaces using the input-to-state stable approach

© 2017 IEEE. This paper proposes an approach to enlarge the impedance range of admittance-type haptic interfaces. Admittance-type haptic interfaces have advantages over impedance-type haptic interfaces in the interaction with high impedance virtual environments. However, the performance of admittance-type haptic interfaces is often limited by the lower boundary of the impedance that can be achieved without stability issue. Especially, it is well known that low value of inertia in an admittance model often causes unstable interaction. This paper extends recently proposed input-to-state stable approach [1] to further lower down the achievable impedance in admittance-type haptic interfaces with less conservative constraint compared with the passivity-based approaches. The primary challenge was identifying the nonlinear hysteresis components which are essential for the implementation of the input-to-state stable approach. Through experimental investigation and after separating and merging the admittance model and the position controller, the partial admittance model (from the measured human force to the desired velocity) and the velocity controller (from the velocity tracking error to the controller force) were found having counter-clockwise hysteresis nonlinear behavior. Therefore, it allows implementing the one-port input-to-state stable (ISS) approach for making both components dissipative and ISS. An additional advantage of the proposed ISS approach is the easiness of the implementation. No model information is required, and the network representation is not necessary, unlike the passivity-based approaches. Series of experiments verified the effectiveness of the proposed approach in term of significantly lowering the achievable impedance value compared with what the time-domain passivity approach can render

Multilateral teleoperation over communication time delay using the time-domain passivity approach

A general framework to stabilize multilateral teleoperation system over a communication time delay based on the well-known time-domain passivity approach (TDPA) is proposed. The uniqueness of this framework is that it is independent of the amount of communication time delay, the multilateral control architecture, and the number of masters and slaves. The multilateral system was first decoupled into subsystems with respect to each terminal by identifying the input signals' contributions to the output terminals, which was not straightforward due to the coupled nature of the multilateral teleoperation system. The decoupled subsystems were then converted into an electrical circuit using a mechanical-electrical analogy. Time-delay power network (TDPN) was introduced to clarify active energy sources from the time delay and passivity observer/passivity controller (PO/PC) was utilized to dissipate those active energies. A less-conservative method compared with prior work was proposed to guarantee the stability. Experiments with a trilateral teleoperation system and with a multilateral teleoperation system with a dual master and dual slave were conducted to validate the proposed framework

Enhancing the Command-Following Bandwidth for Transparent Bilateral Teleoperation

© 2018 IEEE. Enhancing transparency of a teleoperation system by increasing the command-following bandwidth has not received lots of attention so far. This is considered a challenging task since in a teleoperation system the command-following bandwidth of the slave robot motion controller cannot be increased with a conventional motion controller as the desired trajectory is instantaneously commanded by the human user and thus, cannot be considered to be given in a pre-computed, smooth second order derivative form. We propose a method to increase the command-following bandwidth by extending the previously introduced Successive Stiffness Increment (SSI) approach to bilateral teleoperation. The approach allows realizing a very high motion controller gain, which cannot be realized with a conventional bilateral teleoperation controller as confirmed by experimental results

Enhancing the rate-hardness of haptic interaction: Successive force augmentation approach

© 1982-2012 IEEE. There have been numerous approaches that have been proposed to enlarge the impedance range of haptic interaction while maintaining stability. However, enhancing the rate-hardness of haptic interaction while maintaining stability is still a challenging issue. The actual perceived rate-hardness has been much lower than what the users expect to feel. In this paper, we propose the successive force augmentation (SFA) approach, which increases the impedance range by adding a feed-forward force offset to the state-dependent feedback force rendered using a low stiffness value. This allows the proposed approach to display stiffness of up to 10 N/mm with Phantom Premium 1.5. It was possible to further enhance the rate-hardness by using the original value of virtual environment stiffness for feedback force calculation during the transient response followed by normal SFA. Experimental evaluation for multi-DoF virtual environment exhibited a much higher displayed stiffness and rate-hardness compared to conventional approaches. Two user studies revealed that the increase of rate-hardness due to SFA allowed the participants to have a faster reaction time to an unexpected collision with a virtual wall and accurately discriminate between four virtual walls of different stiffness

Bio-inspired knee joint: Trends in the hardware systems development

The knee joint is a complex structure that plays a significant role in the human lower limb for locomotion activities in daily living. However, we are still not quite there yet where we can replicate the functions of the knee bones and the attached ligaments to a significant degree of success. This paper presents the current trend in the development of knee joints based on bio-inspiration concepts and modern bio-inspired knee joints in the research field of prostheses, power-assist suits and mobile robots. The paper also reviews the existing literature to describe major turning points during the development of hardware and control systems associated with bio-inspired knee joints. The anatomy and biomechanics of the knee joint are initially presented. Then the latest bio-inspired knee joints developed within the last 10 years are briefly reviewed based on bone structure, muscle and ligament structure and control strategies. A leg exoskeleton is then introduced for enhancing the functionality of the human lower limb that lacks muscle power. The design consideration, novelty of the design and the working principle of the proposed knee joint are summarized. Furthermore, the simulation results and experimental results are also presented and analyzed. Finally, the paper concludes with design difficulties, design considerations and future directions on bio-inspired knee joint design. The aim of this paper is to be a starting point for researchers keen on understanding the developments throughout the years in the field of bio-inspired knee joints

A robotic test rig for performance assessment of prosthetic joints

Movement within the human body is made possible by joints connecting two or more elements of the musculoskeletal system. Losing one or more of these connections can seriously limit mobility, which in turn can lead to depression and other mental issues. This is particularly pertinent due to a dramatic increase in the number of lower limb amputations resulting from trauma and diseases such as diabetes. The ideal prostheses should re-establish the functions and movement of the missing body part of the patient. As a result, the prosthetic solution has to be tested stringently to ensure effective and reliable usage. This paper elaborates on the development, features, and suitability of a testing rig that can evaluate the performance of prosthetic and robotic joints via cyclic dynamic loading on their complex movements. To establish the rig’s validity, the knee joint was chosen as it provides both compound support and movement, making it one of the major joints within the human body, and an excellent subject to ensure the quality of the prosthesis. Within the rig system, a motorised lead-screw simulates the actuation provided by the hamstring-quadricep antagonist muscle pair and the flexion experienced by the joint. Loads and position are monitored by a load cell and proximity sensors respectively, ensuring the dynamics conform with the geometric model and gait analysis. Background: Robotics, Prosthetics, Mechatronics, Assisted Living. Methods: Gait Analysis, Computer Aided Design, Geometry Models. Conclusion: Modular Device, Streamlining Rehabilitation

Input-to-State Stable Approach for Haptic Interface and Teleoperation Systems

Passivity has been a major criterion on designing a stable haptic interface due to many advantages. However, passivity has been suffering from its intrinsic conservatism since it only represents a small set of the whole stable region. Therefore, there was always limitation to increase the performance due to the small design margin from the passivity criterion. In most of the cases, stability and performance has trade-off relationship. In this thesis, a less conservative control approach is proposed for stable haptic interaction based on Input to State Stable (ISS) criterion. The proposed approach is inspired from the analogy between virtual environments and systems with hysteresis nonlinearities. A system with hysteresis nonlinearity has sector bounded property, which allows us to guarantee that only a finite amount of energy can be extracted from the system, which leads the system to be dissipative [22] and also the states to be bounded by a function of the input [19]. Since the finite amount of energy is allowed to be extracted from the system, the proposed ISS approach has less conservative constraint compared with passivity-based approaches. Moreover, the proposed approach has a simple structure and does not use any system parameters which make it suitable for practical implementations. Furthermore, compared with other passivity-based methods, simulation and experiment results show that the proposed approach increases the dynamic range of impedance in which a stable haptic interface can interact.The presented concept also is extended for stable multi-DOF haptic interaction. In multi-DOF application the concept needs to be applied in each DOF independently to avoid the energy leaking in each DOF. Experimental results show the validity of this concept.Next, I’ve extended the ISS approach to controllers and teleoperation systems. For the controllers, I’ve proposed a framework to revise the input signal based on the selected output signal to make the system bounded. The presented framework determines the sign of the ISS approach feedback to make the system bounded based on the selected output signal. Then based on the extended frame, I’ve shown how the ISS approach can be applied for different architectures of teleoperation systems. A comparison study with POPC proves that the ISS approach provides more transparent teleoperation. For teleoperation systems with time delay, an observer-based ISS approach is introduced to avoid any energy leaking in the system. The extended idea for teleoperation systems is explained and evaluated experimentally for different teleoperation system architectures with time delay

Hybrid force-motion control of coordinated robots interacting with unknown environments

© 2014 Institute of Control, Robotics and Systems (ICROS). This paper presents a unified framework for system design and control in cooperative robotic systems. It introduces a highly general cooperative system configuration involving any number of manipulators grasping a rigid object in contact with a deformable working surface whose real physical parameters are unknown. Dynamics of the closed chain mechanism is expressed based on the object's center of mass, and different robust controllers are designed for position and force control subspaces. The position controller is composed of a sliding mode control term, and involves the position and velocity feedback of end-effector, while the force control is developed based on the highest derivative in feedback methodology. The force controller does not use any derivation of the force signal as well as the internal force controller induced in the system, and it appears to be very practical. Simulation results for two three joint arms moving a rigid object are presented to validate the theoretical results

Input to state stable approach to release the conservatism of passivity-based stable haptic interaction

Passivity has been a major criterion on designing a stable haptic interface due to many advantages. However, passivity has been suffering from its intrinsic conservatism since it only represents a small set of the whole stable region. Therefore, there was always limitation to increase the performance due to the small design margin from the passivity criterion. In most of the cases, stability and performance has trade-off relationship. In this paper, we propose a less conservative control approach for stable haptic interaction based on Input to State Stable (ISS) criterion. The proposed approach is inspired from the analogy between virtual environments and systems with hysteresis nonlinearities. A system with hysteresis nonlinearity has sector bounded property, which allows us to guarantee that only a finite amount of energy can be extracted from the system, which leads the system to be dissipative [1] and also the states to be bounded by a function of the input [2]. Since the finite amount of energy is allowed to be extracted from the system, the proposed ISS approach has less conservative constraint compared with passivity-based approaches. Moreover, the proposed approach has a simple structure and does not use any system parameters which make it suitable for practical implementations. Experimental evaluation validates the effectiveness of the proposed approach

6-DOF extension of memory-based passivation approach for stable haptic interaction

© 2014, Springer-Verlag Berlin Heidelberg. This paper extends previously proposed memory-based passivity approach (MBPA) to 6 degrees-of-freedom (DOF) haptic interactions. By introducing 6-DOF virtual proxy and virtual object, connected with haptic interaction point (HIP), we can extend MBPA to 6-DOF, including torque vs. orientation passivity. To find a passive relationship between positions vs. force graph, instead of position itself, we use position error between the center of mass of the virtual proxy and virtual object. For the angle vs. torque graph, we use angular displacement between the unit vector of the virtual proxy and virtual object instead of angle itself. After the extension, position/angular resolution became a problem, since it depends on configuration of the haptic device. Position resolution should be fixed, and real-time monitoring of every single position change is strongly required in previous MBPA. However, those are difficult requirements when the approach is extended to multi-DOF, especially 6-DOF including orientation. This paper revises the data saving procedure and force bounding mechanism to allow variable position resolution. Position value instead of simple incremental integer is saved together with matched force data into memory space, which allows to interpolate corresponding force value at the releasing trajectory even though it is not in the saved data list. This generalized framework of 6-DOF haptic rendering is evaluated according to simulation results