Joint Angle Sensors Research Articles

Observer based biped walking control, a sensor fusion approach

In humanoid walking research, the prevailing approach is to utilize an abstraction of the robot to a single center of mass (3D linear inverted pendulum mode). Smaller disturbances or an oscillation of the body are typical for a walking robot and must be addressed by an appropriate sensor feedback. To this end, this paper proposes a novel observer fusing joint angle sensors and force sensing resistors. This new method of sensor feedback in a preview control system balances the walk by damping those disturbances and oscillations of the body. Moreover, novel stabilizing methods for defining reference trajectories for the zero moment point and limbs are examined.

A leg proprioception based 6 DOF odometry for statically stable walking robots

This article presents a 3D odometry algorithm for statically stable walking robots that only uses proprioceptive data delivered by joint angle and joint torque sensors embedded within the legs. The algorithm intrinsically handles each kind of emerging statically stable gait and is independent of predefined gait patterns. Additionally, the algorithm can be equally applied to stiff robots as well as to robots with compliant joints. Based on the proprioceptive information a 6 degrees of freedom (DOF) pose estimate is calculated in three steps. First, point clouds, represented by the foot positions with respect to the body frame at two consecutive time steps, are matched and provide a 6 DOF estimate for the relative body motion. The obtained relative motion estimates are summed up over time giving a 6 DOF pose estimate with respect to the start frame. Second, joint torque measurement based pitch and roll angle estimates are determined. Finally in a third step, these estimates are used to stabilize the orientation angles calculated in the first step by data fusion employing an error state Kalman filter. The algorithm is implemented and tested on the DLR Crawler, an actively compliant six-legged walking robot. For this specific robot, experimental data is provided and the performance is evaluated in flat terrain and on gravel, at different joint stiffness settings and for various emerging gaits. Based on this data, problems associated with the odometry of statically stable walking robots are identified and discussed. Further, some results for crossing slopes and edges in a complete 3D scenario are presented.

Data Fusion Based on Optical Technology for Observation of Human Manipulation

The adoption of human observation is becoming more and more frequent within imitation learning and programming by demonstration approaches (PbD) to robot programming. For robotic systems equipped with anthropomorphic hands, the observation phase is very challenging and no ultimate solution exists. This work proposes a novel mechatronic approach to the observation of human hand motion during manipulation tasks. The strategy is based on the combined use of an optical motion capture system and a low-cost data glove equipped with novel joint angle sensors, based on optoelectronic technology. The combination of the two information sources is obtained through a sensor fusion algorithm based on the extended Kalman filter (EKF) suitably modified to tackle the problem of marker occlusions, typical of optical motion capture systems. This approach requires a kinematic model of the human hand. Another key contribution of this work is a new method to calibrate this model.

Die Dynamik der Bewegungsabläufe der Fingergelenke beim Faustschluss

The purpose of this study was to analyse motion patterns of the finger joints dynamically while making a fist. 10 subjects were examined using the TUB-sensor glove, which was equipped with 14 joint angle sensors. The median time it takes the finger joints to complete flexion until reaching the state of a closed fist ranges between 0.5 to 1.0 s. A specific pattern can be seen for every finger. The PIP and DIP joints appear to be linked, with the DIP trailing the PIP joint. At the thumb the IP is trailing the MCP joint. The MCP joint shows more variation at the beginning of flexion: while in some cases it initiates movement in a finger, in other cases its flexion falls behind the PIP joint movements. The completion of flexion is achieved by the MCP joints, with the PIP and DIP joints reaching their end of motion first. The range of motion (ROM) at the MCP joints shows a finger-dependent median of 79-97°. At the PIP joints the median lies between 87° and 90°, at the DIP joints between 52° and 68°. At the thumb it is 21° for the MCP and 24° for the IP joint. The linkage between PIP and DIP joints can also be seen when analysing the ROM. The coupling ratio amounts to 0.77 at the index finger, 0.75 at the middle and ring finger and 0.57 at the small finger.

Optimization and evaluation of a proportional derivative controller for planar arm movement

In most clinical applications of functional electrical stimulation (FES), the timing and amplitude of electrical stimuli have been controlled by open-loop pattern generators. The control of upper extremity reaching movements, however, will require feedback control to achieve the required precision. Here we present three controllers using proportional derivative (PD) feedback to stimulate six arm muscles, using two joint angle sensors. Controllers were first optimized and then evaluated on a computational arm model that includes musculoskeletal dynamics. Feedback gains were optimized by minimizing a weighted sum of position errors and muscle forces. Generalizability of the controllers was evaluated by performing movements for which the controller was not optimized, and robustness was tested via model simulations with randomly weakened muscles. Robustness was further evaluated by adding joint friction and doubling the arm mass. After optimization with a properly weighted cost function, all PD controllers performed fast, accurate, and robust reaching movements in simulation. Oscillatory behavior was seen after improper tuning. Performance improved slightly as the complexity of the feedback gain matrix increased.

Triple Stance Phase Displacement Analysis With Redundant and Nonredundant Sensing in a Novel Three-Legged Mobile Robot Using Parallel Kinematics

This paper presents the forward and inverse displacement analysis of a novel three-legged walking robot Self-excited Tripedal Dynamic Experimental Robot (STriDER) in its triple stance phase. STriDER utilizes the concept of passive dynamic locomotion to walk, but when all three feet of the robot are on the ground, the kinematic configuration of the robot behaves like an in-parallel manipulator. To plan and control its change in posture, the kinematics of its forward and inverse displacement must be analyzed. First, the concept of this novel walking robot and its unique tripedal gait are discussed, followed by the overall kinematic configuration and definitions of its coordinate frames. When all three feet of the robot are on the ground, by assuming there is no slipping at the feet, each foot contact point is treated as a passive spherical joint. Kinematic analysis methods for in-parallel manipulators are briefly reviewed and adopted for the forward and inverse displacement analysis for this mobile robot. Both loop-closure equations based on geometric constraints and the intersection of the loci of the feet are utilized to solve the forward displacement problem. Analytical solutions are identified and discussed in the cases of redundant sensing with displacement information from nine, eight, and seven joint angle sensors. For the nonredundant sensing case using information from six joint angle sensors, it is shown that analytical solutions can only be obtained when the displacement information is available from unequally distributed joint angle sensors among the three legs. As for the case when joint angle sensors are equally distributed among the three legs, it will result in a 16th-order polynomial with respect to a single variable, and closed-form forward displacement solutions can be obtained. Finally, results from the simulations are presented for both inverse displacement analysis and the nonredundant sensing case with equally distributed joint angle sensors. It is found that at most 16 forward displacement solutions exist if displacement information from two joint angle sensors per leg are used and one is not used.

弾性関節を持つロボットマニピュレータのマルチレートフィードフォワード制御系の実現

This paper introduces a novel multirate feedforward control method for robot manipulators with elastic joints. Perfect tracking control methodology using multirate feedforward control was proposed by H. Fujimoto, et al. Then, A. Shimada, et al. have prsented its application to robot manipulators; however, they only described the controller design process and gave a few simulation results. In addition, they did not provide details on how the state reference should be designed. Even if experiments were attempted, it would be difficult to evaluate control performance since generally manipulators have joint angle sensors mounted on the output side of reduction gears In order to solve this, this paper illustrates the design process for the state reference, and introduces a prototype robot manipulator that has precision rotary encoders installed on the output side of the joints. This means that the manipulator has not only the rotary encoders attached to servo motors but special precision rotary encoders. We describe experimental results obtained by applying this control technique.

AUTONOMOUS EXCAVATION USING HYDRAULIC MOBILE MACHINE RETROFITTED WITH ELECTRONIC CONTROL SYSTEM

Autonomous functions are a common research topic in robotics. However, the robots typically have limited operating conditions and they can only handle relatively small loads. Many autonomous control concepts are applicable to actual construction machinery. The benefits would be considerable regarding efficiency, safety, and operator comfort. The research projects of this field have often led to systems with cost and complexity too high for most applications. This paper presents an implementation of a cost-effective distributed control system that is retrofitted to a small hydraulic excavator. The system can be used to perform simple operator assisting functions but also to develop autonomous excavation.The hardware of the system consists of cost-effective joint angle sensors and a flexible microcontroller unit. Control schemes that produce autonomous functions are discussed and tested with the excavator. These include position controllers for conventional mobile proportional hydraulics. The aim is to find computationally simple but flexible algorithms for autonomous excavation. The results of the preliminary tests are presented. Future improvements are discussed.

A FRAMEWORK FOR GRASP SIMULATION AND CONTROL IN DOMESTIC ENVIRONMENTS

A service robot for a domestic environment should be able to grasp, move, and release objects. To successfully grasp objects that cannot be expected to be perfectly modelled and whose positions are not exactly known, control algorithms need to handle uncertainty. Such controllers often use information from force/torque, tactile and joint angle sensors. This paper presents a simulation environment and proposes a design approach for controlling robotic grasping under those conditions. Finally, results from simulation of a sample task are presented.

Real-time control of a virtual hand

A myoelectric control system for prostheses was developed and evaluated on six healthy subjects. These were able to control a computer-animated hand in real-time with a 20 Hz update rate. A data glove, equipped with joint angle sensors, was used to train the system and to evaluate the continuous predictions of joint angles. A linear envelop filter was used for EMG signal pre-processing and the recognition of muscle patterns was carried out with local approximation using the lazy algorithm. Furthermore, an on-line learning was used to provide feedback to the subjects. The results show that the subjects increased their performance during the experiment and all subjects performed eight or more movements with 100% accuracy in their last recording session. The final median delay for the predicted hand joint positions, compared with the recorded, was in the range of 50 to 100 ms. Off-line evaluation has earlier been done on amputees while using a data glove on the contralateral hand. The real-time control system outlined in this paper offers an effective myoelectric prosthesis control that is suitable for a miniaturized low cost implementation.This paper is a part of a ongoing development and refinement of hand prosthesis carried out within the Artificial Hand Project. (Less)

SENSORS, IDENTIFICATION, AND LOW LEVEL CONTROL OF A FLEXIBLE ANTHROPOMORPHIC ROBOT HAND

The successful control of a robot hand with multiple degrees of freedom not only requires sensors to determine the state of the hand but also a thorough understanding of the actuator system and its properties. This article presents a set of sensors and analyzes the actuator properties of an anthropomorphic robot hand driven by flexible fluidic actuators. These flexible and compact actuators are integrated directly into the finger joints, they can be driven either pneumatically or hydraulically. The sensors for the measurement of joint angles, contact forces, and fluid pressure are described; the designs utilize mostly commodity components. Hall sensors and customized half-ring rare-earth magnets are used to integrate the joint angle sensors directly into the actuated joints. A force sensor setup allowing soft finger surfaces is evaluated. Fluid pressure sensors are needed for the model-based computation of joint torques and to limit the actuator pressure. Static and dynamic actuator characteristics are determined in a theoretical process analysis, and suitable parameters are identified in several experiments. The resulting actuator model incorporates the viscoelastic material behavior and describes the relations of joint angle, actuator pressure, and actuator torque. It is used in simulations and for the design of a joint position controller.

Joint motion and reacting forces in the carving ski turn compared with the conventional ski turn

Joint angle motion and reacting forces in the ski turn using a ‘carving ski’ with short side curve radius have been measured to be compared with those in a turn using a conventional ski which has a long side curve radius. The measurements were made using specially developed joint angle sensors attached to the skier’s leg and a force sensor fitted between the binding plate and the ski. In a long turn using a carving ski, the skier creates a larger difference between the outer leg extension and the inner leg flexion with no thigh rotation. Reacting force is uniform in the outer ski and also applied on the rear of the inner ski. However, the forward resistant force is larger in the carving ski turn. In the case of a long turn using a conventional ski, there is thigh rotation, larger abduction and smaller difference between the flexion of both legs. A relatively large force is applied to the front part of the ski. The joint motion in the carving ski turn is simple and it is easy for skiers to turn without skidding in the parallel long turn. In the short turn using a carving ski, the skier makes a gradual change in the thigh rotation. The outer leg continues flexion when it changes to the inner leg. Force also changes gradually over a small range. In the short turn using a conventional ski, the skier makes a quick rotation of the thigh in the early part of the turn. The reacting force occurs instantly and its amplitude of change is larger. The joint motion using the carving ski is moderate with no impact resistance. This will help skiers to make smooth and effective short turns.

Structured sleeve for repair of implantable in-line connectors.

A structured miniature repair sleeve has been designed for implantable in-line connectors that develop small current leaks post-implant. The repair sleeve has been successfully utilised in one subject following the development of current leakage in connectors on an implanted joint angle sensor.

Analysis of the electromyographic activity of human elbow joint muscles during slow linear flexion movements in isotorque conditions

Electromyograms were recorded by surface electrodes from the mm. biceps brachii (caput longum et breve), brachioradialis and triceps brachii (caput longum) in 10 healthy human subjects during slow linear movements in the elbow joint against a weak extending torque. The test movements were carried out under visual control through combining on a monitor screen a signal from a joint angle sensor with an appropriate command generated by a computer. The movements were fulfilled against a weak constant extending torque (0.5–2.5 Nm) and the extensor muscles were inactive. Surface electromyograms were full-wave rectified, filtered and averaged within sets of 10 identical tests. For the test movements in the range from 20° to 100° (0° corresponds to a completely extended joint in these designations) the dynamic components of the efferent commands to actively contracted muscles frequently had a well-expressed monotonous increase. The electromyography intensity during movement quite often increased exponentially in all three investigated flexors. At the same time, the averaged electromyograms in one or two muscles could contain non-monotonous oscillations, thus showing a well-expressed decrease in the intensity of the efferent inflow within a middle range of a movement phase. The non-monotonous oscillations could occur in some subjects under minimal loads (0.5–0.75 Nm); they usually appeared initially only in one muscle, whereas the frequency of their occurrence was not high. The probability of finding the non-monotonous oscillations in the electromyograms from the muscles under study increased with heightening the extending load. Under the loads of 2.0–2.5 Nm this type of reaction could be found in almost half of all records (for the three muscles in each of the 10 subjects under testing). The presence of noticeable non-monotonous components in the electromyograms of the elbow flexors during their contraction is probably connected to their biomechanical arrangement within the joint. It is known that the arms of the forces generated by elbow flexors are maximal in the middle range of joint angles and decrease with a change in angle in both directions. Thus, we can suppose that non-monotonous decrement components in the electromyograms of the elbow flexors are presumably connected with an obvious necessity for a subject to decrease the excitatory efferent inflow to the muscles in the middle range of the joint angles. The pattern of electromyograms in the flexors acting around the joint was also dependent on a redistribution of activity between agonists. In the subjects showing stable non-monotonous components on the averaged electromyogram records in two agonists, a redistribution of the activity between these muscles has been demonstrated when phases of the electromyogram diminishing in one of them coincided with the appropriate increments in the other.

A Study on Tele-Existence of the Tactile Sense

This report describes, first, a glove with joint angle sensors made of chip coils to detect the joint angles of human fingers in real time and also describes artificial fingers with multiple joints used for a tele-existence system on the tactile sense. Characteristics of the artificial skin to be attached to the artificial fingers are based on the experimental results of force-displacement characteristics of the human skin. Secondly, sensations produced by the pressure and the strain applied to the finger tip surface were measured as functions of pressure force level and the direction of the strain force using psychophysical techniques. A study of pressure sense and a force vector sensor is useful from the view point of the tele-existence system for the tactile sense.

Movement-related and steady-state electromyographic activity of human elbow flexors in slow transition movements between two equilibrium states

The electromyograms were recorded in healthy human subjects by surface electrodes from the mm. biceps brachii (caput longum et. brevis), brachioradialis, and triceps brachii (caput longum) during slow transition movements in elbow joint against a weak extending torque. The test movements (flexion transitions between two steady-states) were fulfilled under visual control through combining on a monitor screen a signal from a joint angle sensor with a corresponding command generated by a computer. Movement velocities ranged between 5 and 80°/s, subjects were asked to move forearm without activation of elbow extensors. Surface electromyograms were full-wave rectified, filtered and averaged within sets of 10 identical tests. Amplitudes of dynamic and steady-state components of the electromyograms were determined in dependence on a final value of joint angle, slow and fast movements were compared. An exponential-like increase of dynamic component was observed in electromyograms recorded from m. biceps brachii, the component had been increased with movement velocity and with load increment. In many experiments a statistically significant decrease of static component could be noticed within middle range of joint angles (40–60°) followed by a well expressed increment for larger movements. This pattern of the static component in electromyograms could vary in different experiments even in the same subjects. A steady discharge in m. brachioradialis at ramp phase has usually been recorded only under a notable load. Variable and quite often unpredictable character of the static components of the electromyograms recorded from elbow flexors in the transition movements makes it difficult to use the equilibrium point hypothesis to describe the central processes of movement. It has been assumed that during active muscle shortening the dynamic components in arriving efferent activity should play a predominant role. A simple scheme could be proposed for transition to a steady-state after shortening. Decrease of the efferent inflow can evoke internal lengthening of the contractile elements in muscle and, as a result, hysteresis increase in the muscle contraction efficiency. Effectiveness in maintenance of the steady position seems to also be enhanced due to muscle thixotropy and friction processes in the joint. Hysteresis after-effects in elbow flexors were demonstrated as a difference in steady-state levels of electromyograms with oppositely directed approaches to the same joint position.

Analysis of Hand Tool Grips

An efficient measurement and evaluation system for hand tool tasks can provide a practical solution to the problem of designing and evaluating manual tool tasks in the workplace. Such a prototype system, termed the data glove, was developed by overlaying twelve Force Sensitive Resistors on an posture-measuring glove (Cyberglove™, Virtual Technologies, 1992) with eighteen joint angle sensors. To validate the data glove, hand posture and grip force was measured on sixteen different cylindrical grip tasks for six subjects. A factor analysis of the grip force distributions on the hand indicated that three major areas of force concentration occurred: 1) an area of high force levels termed the ‘active’ area, 2) an area of intermediate force levels termed the ‘support’ area, and 3) an area of low force levels termed the ‘inactive’ area. The different grips were also classified and ranked for levels of radian/ulnar deviation torques and flexion/extension torques, and then combined with the force information to yield a pattern of grip degradation with increasing levels of grip stress. A validation experiment comparing the data glove force output with the muscle surface EMG measurement yielded a significant, high correlation between the two measures.

Synthetic viewing: comprehensive work representation, making remote work clearer to the operator

Maintenance work in fusion plants such as the ITER plant will be carried out fully remotely, without any direct view on to the work scene. The basic sources of information about the state of the work are video monitors. In a first development step, this viewing channel was enhanced by three-dimensional computer graphics controlled by signals of motion sensors (such as joint angle sensors) of the real maintenance devices. However, experience has shown that more information is required about the status of all pieces of equipment involved and about the status of the entire handling task, if the work is to be done properly. Viewing for remote handling applications needs to include the display of such status information in a suitable form. Of special importance in this sense is the representation of the work procedures on the computer display, enabling the operator to grasp at a glance the actual state of the work and the details about the subtask to be executed next. The tool providing this “synthetic” viewing but also task-suited to planning, training and controlling support for the operator is the remote handling workstation. The prototype of a remote handling workstation was successfully used in the first complete Karlsruhe experiment for in-torus handling.

End-point position measurements of long-reach flexible manipulators

This paper describes the design, testing and evaluation of a position measurement system for a large flexible manipulator. Previous work is reviewed and updated with a discussion of related sensors and their applicability. Two approaches to accurately measure end-point position over a large workspace are outlined. The chosen approach estimates the tip position from joint angle and link deflection sensors. The equipment used (e.g. sensors, illumination, focusing optics, etc.) and the calibration procedure are presented. Two evaluations of the system are discussed. First static link deflection measurements are compared to results of a static deflection model. Second the combined tip position estimate is compared to an absolute measurement taken with a dial indicator. The paper finishes with a description of expected applications for manipulator control.

Estimation of Position and Orientation of an Object Grasped by a Parallel-Jaw Gripper.

In this paper we propose an algorithm for estimating the position and orientation of a polyhedral object grasped by a parallel-jaw gripper. In order to estimate the object's vertex positions, we propose a method that rotates the object around the object's vertex in contact with the external environment. The vertex positions are estimated by joint angle sensor information. We also propose an analytical method for deriving the position and orientation of the object with respect to the hand coordinate system from the vertex positions. In our formulation, the estimation problem becomes linear equations subject to the constraint that a matrix is orthogonal. A case where the data are contaminated with noise is also treated, and the optimal solution is explicitly given.