High-Precision Absolute Pose Sensing for Parallel Mechanisms.

Position control of an underactuated manipulator that has one passive joint is investigated. The dynamic constraint caused by the passive joint is second-order nonholonomic. Time-scaling of the active joint trajectory and bi-directional motion planning from the initial and the desired configurations provide an exact solution of the positioning trajectory. The active and passive joints can be positioned to the desired angles simultaneously by swinging the active joints only twice. Feedback control constrains the manipulator along the planned path in the configuration space. Simulation and experimental results show the validity of the proposed methods.

Position control of an underactuated manipulator that has one passive joint is investigated. The dynamic constraint caused by the passive joint is second-order nonholonomic. Time-scaling of the active joint trajectory and bi-directional motion planning from the initial and the desired configurations provide an exact solution of the positioning trajectory. The active and passive joints can be positioned to the desired angles simultaneously by swinging the active joints only twice. Feedback control constrains the manipulator along the planned path in the configuration space. Simulation and experimental results show the validity of the proposed methods.

A method is proposed for controlling the position of a manipulator with passive joints that have holding brakes instead of actuators. In this method, the coupling characteristics of manipulator dynamics are used, and no additional mechanisms are required. The effectiveness of the method was verified by experiments using a prototype manipulator. The prototype is a two-degree-of-freedom, horizontally articulated manipulator. The first axis is an active joint, and the second axis is a passive joint. While the brake of the passive joint is released, the passive joint is indirectly controlled by the motion of the active joint through the use of dynamic coupling. While the brake is engaged, the active joint is controlled. By combining these two control modes, the total position of the manipulator is controlled. The experiments show that use of this method makes the precise positioning of the passive joints possible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The authors propose a method of controlling the position of a manipulator with passive joints which have holding brakes instead of actuators. In this method, the coupling characteristics of manipulator dynamics are used, and no additional mechanisms are required. In the paper, the effectiveness of the method is verified by experiments using a prototype manipulator. The prototype is a two degree of freedom horizontally articulated manipulator. The first axis is an active joint and the second axis is a passive joint. While the brake of the passive joint is released, the passive joint is indirectly controlled by the motion of the active joint, through the use of dynamic coupling. While the brake is engaged, the active joint is controlled. By combining these two control modes, total position of the manipulator is controlled. The experiments show that the precise positioning of the passive joint is feasible by use of the proposed method. >

Snake-like robots have good properties to move on rough terrain. Their low-height bodies and articulated structures are proper to go into narrow space and to climb over obstacles. Thus, many applications of articulated mobile robots are expected (e.g. rescue robots). One of the types of snake-like robots named 'Genbu' consists of active wheels and passive jointed multi bodies. We classified this type of snake-like robots as active wheel passive joint articulated mobile robot. Although Genbu cannot go over wide gaps, they have high durability because their joints are not activated with gear-head motors. So, Genbu has high mobility on rough terrain at high-speed. Moreover the long articulated structure is proper to climb over obstacles because of size effect. For example, Genbu 2 equipped with 220mm diameter wheels can climb 300mm vertical wall. These characteristics are proper to use as rescue robots or planetary rovers. However these applications require semi-autonomous robots because the operator cannot approach the robots. The control method of this type of snake-like robots has not been established yet. In order to establish the control method, detecting the posture of the robot is very important. Nevertheless, Genbu 2 was difficult to detect the posture because of the elastic body join is. In addition, Genbu 2 had some problems for practical use (e.g. motor drivers are not inside). In this study, Genbu 3 was newly developed to solve these problems. In order to accomplish these purposes, the passive rigid joints for detecting the posture, and torque sensor with float differential mechanism are newly developed for Genbu 3. In this paper the mechanism of Genbu 3 and basic running experiments of Genbu 3 are described.

Effects of toe stiffness on ankle kinetics in a robotic transtibial prosthesis during level-ground walking

This paper describes the development of a wearable exoskeleton system for the lower extremities of infantry soldiers and proposes appropriate design criteria based on existing case studies. Because infantry soldiers carry a variety of equipment, the interference with existing equipment and additional burden of the exoskeleton support system should be minimized. Recent studies have shown that a user only needs to be supported in the gravitational direction when walking on flat terrain; however, active joints are necessary to support walking over rough and sloped terrain such as mountains. Thus, an underactuated exoskeleton system was considered: passive joints are applied to the hip and ankle joints, and active joints are applied to the knee joints to exploit the dynamic coupling effect of the link structure and muscular activation patterns when the user is going up and down stairs. A prototype of the exoskeleton system was developed and validated through a simple stair-climbing experiment.

This paper presents a wearable exoskeleton upper limb rehabilitation robot that consists of eight active joints and one passive joint. Each active joint is driven by two pneumatic muscles (PMs) in opposing pair configuration and each PM drives the joint through a steel wire with a flexible sleeve and a tension device. These factors incorporate with characteristics of PM make the rehabilitation robot system very complex (nonlinear, time-varying, and time-delay). In this paper, the friction force and characteristics of open-loop control of one of the robotic joints has been studied. The quasi-static model of the robotic joint have been established based on experimental methods. In addition, the performances of three control modes have also been researched. These works would be helpful to the future work such as the control of the rehabilitation robot.

Impairments in ankle joint position sense along with muscle weakness greatly affect the recovery of balance among stroke survivors. Elastic therapeutic taping has been studied in musculoskeletal conditions of the ankle to improve joint position sense and its effects in stroke are not known. The aims of the study were to investigate the differences in joint position sense between paretic and nonparetic ankles and to examine the effects of elastic therapeutic taping on joint position sense of the paretic ankle in stroke survivors. Sixteen chronic stroke survivors participated in a 2-day protocol of ankle elastic therapeutic taping on the paretic side. Active and passive joint position sense at the ankle was measured by Biodex Isokinetic III system on both the paretic and nonparetic sides before elastic therapeutic taping and only the paretic side after elastic therapeutic taping. The active and passive ankle joint position sense values were significantly (P < 0.001) lower on the paretic side than the nonparetic side before intervention. Joint position sense significantly (P < 0.001) improved for the paretic ankle after elastic therapeutic taping. Chronic stroke survivors were deficient in ankle joint position sense on the paretic side. Elastic therapeutic taping was effective in the short term to improve active and passive joint position sense.

Kinematic analysis of parallel mechanisms at singular points where a connecting chain has local mobility

The existing industrial robots are usually short of force control, which makes them unsuitable for the continuous contact operations. This paper presents a 3-DOF Translational Force-controlled End-effector (TFE) for robots, which is based on 3-P(UU)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Parallel Mechanism (PM). The active joint is driven by the hybrid actuator with pneumatic cylinder inside the voice coil motor. Both the forward and inverse kinematic models are established. The pneumatic and magnetic forces are matched according to the force spatial distribution. Under the constraints of kinematics, singularity, geometric interference, the PM sizes are optimized to enhance the motion workspace and average output force, and to reduce the force variance. Then the robust adaptive force tracking admittance control method is studied to improve output force accuracy and stability. Simulation results demonstrate that the quasi-cubic working area without singularity inside the workspace reaches 18 mm×21 mm×22 mm. The output force tracks the command without steady-state error, and recovers rapidly under the environmental impact. The methods proposed for the 3-DOF PM optimization and pneumatic-electric matching effectively improve the performance of the TFE, and are great of significance to robotic grinding and polishing applications for complex surfaces in narrow spaces.

An innovative lower extremity exoskeleton, SJTU-EX, is demonstrated in Shanghai JiaoTong University, which mainly aims to help soldiers and workers to support a payload in motion. This paper summarizes the mechanical design of SJTU-EX. Each pseudo-anthropomorphic leg of SJTU-EX has four active joints and two passive joints, and the joint ranges are optimized in consideration of both safety factors and the realization of typical motions. Springs are applied in the leg to eliminate the effect of gravity. The results of dynamic simulations are used to determine the actuated joints and the passive joints. Novel Hy-Mo actuators are introduced for SJTU-EX and the layout of the actuator for Diamond Side 2 is described in detail as a design example.

In this paper, a novel wearable lightweight exoskeleton with full degrees of freedom for upper-limb power assistance is developed. It is controlled by surface electromyography(sEMG) signals of the agonist muscle alone and aims to provide 30% power assistance to the elbow and shoulder joints for the flexion/extension movement. In the exoskeleton, there are two wearable identical arms and a back support pack. Each arm consists of two active joints and four passive joints, in which the active joints implement the power assistance for flexion/extension movement of the elbow and shoulder joints, whereas the passive joints fully follow the wearer's other motions. Moreover, with a rotatable and telescopic mechanism, the joint axis of the elbow joint of the exoskeleton can be adjusted to coincide with the elbow joint for different wearers, and meanwhile the passive joints of the shoulder complex of the exoskeleton can guarantee its instantaneous center of rotation to coincide with that of the wearer. As a result, the developed exoskeleton eliminates the restriction of motion and then the discomfort of the wearer. In addition, an extended admittance control is introduced and the effectiveness of the power assistance is verified.

In-parallel systems can have some active and some passive joints (i.e., joints with and without joint actuators). The questions that we address in this paper are: how to choose the active and passive joints, how to know whether a set of active joints is sufficient, redundant, or minimal to control the end-effector, and whether there exists a unique choice of active actuators. Our approach to study this problem is based on instantaneous properties of series chains as derived from the theory of screw systems. In this framework, we identify those screws that correspond to the joint actuators of the component series chains. Once the correspondence is made, the sought after actuator properties are deduced from the vector space properties of these screws.

This chapter concerns the swing-up control of an n-link revolute planar robot with any one of the joints being passive. The goal is to design and analyze a swing-up controller that can bring the robot into any arbitrarily small neighborhood of the upright equilibrium point, where all the links are in the upright position. This chapter presents a unified solution based on the notion of virtual composite link (VCL), which is a virtual link made up of one or more active links. By using the angles of two series of VCLs separated by the passive joint and using the total mechanical energy of the robot, this chapter designs a swing-up controller and analyzes the global motion of the robot under the controller. This chapter presents a lower bound for each control gain related to the angle of each VCL such that the closed-loop system has only one undesired equilibrium point in addition to the upright equilibrium point, and presents an original proof of the conditions on the control gains for a class of n-link underactuation-degree-one planar robots with an active first joint. This chapter provides a bigger control gain region for achieving the control objective than those of previous results on 3- and n-link robots with a passive first joint.