Hard contact surface tracking for industrial manipulators with (SR) position based force control

The walking procedure of the cattle, Bostaurus, on a paddy field before spring plowing was captured with a high-speed video camera. The properties of the paddy soil used for tests and the geometrical configurations of the hooves of the cattle were examined. The geometrical configurations and motion postures of the cattle during walking on paddy field were analyzed, and the gait parameters were gained from the high-speed photographs. The changes of displacement, velocity, acceleration and force of the centre of mass (COM) of the cattle were analyzed. The changes of the joint angles and the orientations of all limbs were analyzed. It was shown that the changes of hip joint angle and shoulder joint angle were more remarkable, which provided the driving force for the body. The changes of the forelimb were more prominent compared with the hind-limb, moreover, the landing place of the hind-hooves were farther than the fore-hooves, which made the hind-limb have a larger movement space to prevent the interference between forelimb and hind-limb while the strides were increased. The movement of knee joint and elbow joint were very obvious after limb left the ground, the movements of hip joint and shoulder joint were steady to reduce the impact of the ground before limb touched down the ground. The results would provide some theoretical and practical references for biomimetic design for improving the reasonable motion of the walking robot on soft ground. This work may provide the basic theory in developing cattle-like robot in structural design. Besides, it provides an important reference to study the other bionic robots.

In this paper, we formulate a design for a hybrid force-position controller (HFPC) for a hydraulically actuated excavator arm and perform simulative validation of the proposed approach. The concept of an HFPC by Raibert et al. [1] is adapted for a hydraulically actuated system and reformulated in order to enable path tracking. The result is a control regime which steers the controlled member, i.e., the tool center point (TCP), along an arbitrary trajectory where the force controlled vector points tangentially or orthogonally to the trajectory and the position controlled vectors are perpendicular toward the force direction. The controller incorporates a computed torque controller (CTC) [2, p. 174 et sqq.] compensating for conservative forces as well as inertia and Coriolis forces. Due to the selected actuation method of hydraulic cylinders, the torque requirements are transformed into velocity and pressure requirements. In order to control both velocity and pressure, individual control at inlet and outlet of the cylinders is necessary. This is accomplished with an independent metering valve control system. The performance of the developed system is evaluated on two use cases—the collision with a rigid object and the limitation of the resulting contact force and the sliding along a surface with a defined orthogonal force. In both cases, the expected force control behavior is achieved while maintaining system stability when switching between the control regimes.

Position control was applied to industrial robots when they carry out tasks such as handling, stacking, welding. However, carrying out complex tasks like grinding, polishing and deburring requires more. In these cases, the contact force, between the manipulator's end effector and the working environment, also needs to be controlled to achieve compliance. The surface tracking based on force control is the key technology for industrial robots to perform tasks like grinding, polishing. Force control requires robots to sense the information of the external environment. In this paper, a Six-Axis Force/Torque Transducer is used to acquire the contact force between the tool and the surface. Then we use the constant contact force control algorithm, together with the orientation adjustment strategy, to keep the contact force constant and ensure the tool vertical to the contact surface to realize the surface tracking. Experiments show that the scheme is efficient, and has a certain guiding significance for manipulator in industrial production tasks where force control is required.

This paper presents a position-based force control scheme for human-to-robot object handover. The development of a framework for the robotic behavioural control strategy was initially based on the understanding dynamically and kinematically on an equivalent human-human object handover task. A real-world object handover task has been carried out to develop the conceptual guideline for a human-like behaviour-based robot. The control approach provides feasible and reliable solution for performing contact tasks between the human and robot. The control scheme is made up of an outer force control loop and an internal position-based control loop. Additionally, proportional plus integral (PI) and fuzzy logic control (FLC) algorithms were adopted to the compliance control the robot end effector’s position and interactive force in real-time. The quantitative measurements of the controlled robot performance based on PI ad FLC can be considered acceptable for human-to-robot object handover since the robot can receive the object from the human in a safe, reliable and timely manner.

The primary sources of injuries in the workplace are improper manual material handling (MMH) motions, forklift collisions, slip, and fall. This research presents a Digital Twin (DT) framework to analyze fatigue in humans while performing lifting MMH activity in a laboratory environment for the purpose of reducing these types of injuries. The proposed methodology analyzes the worker’s body joints to detect biomechanical fatigue as a factor of change in back, elbow, and knee joint angles. Using the dynamic time warping (DTW) algorithm, the change in joint angles with time was analyzed. The variation in DTW parameters was evaluated using exponentially weighted moving average (EWMA) control charts for further analysis. A preliminary study considering two healthy male subjects performing seven experiments, each under an optical motion capture system was performed to test the model’s efficiency. Our contributions are twofold. First, we propose a model to detect biomechanical fatigue in the subjects performing MMH lifting activity as a change in joint angles. Secondly, the research also shows evidence that different individuals show signs of body fatigue via different body joints and showcases the need for a true personalized DT for an operator for fatigue assessment in an MMH environment.

This study aims to analyze the effect of mental fatigue on biomechanical variables of batting technique in softball. Good batting technique requires precise movement coordination, reaction speed, and high mental concentration. However, mental fatigue, which often occurs due to intensive cognitive activity or excessive mental load, is thought to affect biomechanical performance. This includes changes in joint angles, body rotation speed, and batted ball speed, which directly affect the effectiveness of batting in softball. This study involved 15 softball players from the Bumi Asri club with an average age of 20 ± 0.6 years. Data collection was carried out using a three-dimensional motion analysis device, ball speed radar, and heart rate sensor. Subjects will undergo a 15-minute warm-up session, followed by an intensive cognitive task designed to trigger mental fatigue. Biomechanical variables will be measured before and after mental fatigue, including analysis of changes in joint angles, body rotation speed, and batted ball speed. The data obtained will be analyzed using a paired sample t-test to evaluate significant differences. This study is expected to provide an important contribution in understanding the impact of mental fatigue on sports biomechanics, especially softball batting technique. In addition, the results of this study can be a basis for coaches to design more effective training strategies, so that athletes can maintain optimal performance even in challenging mental conditions.

Chronic trauma-induced neck pain impairs the neural control of the deep semispinalis cervicis muscle

Although exercise can be effective for relief of neck pain, little is known about the effect of exercise on the neural control of neck muscles. A randomized controlled trial was conducted on 46 women with chronic neck pain to investigate the immediate effectiveness of an 8-week exercise programme on pain and directional specificity of neck muscle activity. At baseline, the patients completed questionnaires including the neck disability index (NDI) and performed a circular contraction of their head in the horizontal plane at 15 N force, with continuous change in force direction in the range 0-360°. Electromyography (EMG) was recorded from the sternocleidomastoid (SCM) and splenius capitis (SCap) muscles. Tuning curves of the EMG amplitude were computed, which depicts muscle activity over a range of force directions. The mean point of the tuning curves defined a directional vector, which determined the specificity of muscle activity. Patients were randomly assigned either to a training or control group. A significant between-group difference in the change in NDI was observed. A reduction in NDI was observed following training (pre: 18.2 ± 7.4; post: 14.1 ± 6.5; p < 0.01) but not for the control group (pre: 17.5 ± 6.3; post: 16.6 ± 7.4). The training group showed higher specificity of muscle activity post-intervention (pre: 18.6 ± 9.8%, post: 24.7 ± 14.3%; p < 0.05), whereas no change occurred for the control group (pre: 19.4 ± 11.9%, post: 18.2 ± 10.1%). An exercise programme that aims to enhance motor control of the cervical spine improves the specificity of neck muscle activity and reduces pain and disability in patients with neck pain.

In hybrid control of robot manipulators separate controllers are designed for force and position errors control. Controllers are designed either in task or joint space and their outputs combine to provide input torque to the manipulator. Position and force controllers performance in a constrained robotic task is affected by their interaction to a degree dependent on the controller's ability to reject disturbances. Ideally, decoupling of the two control loops is desired to achieve the best performance in position and force directions. In this article, analysis of control loop interactions is performed for contact and noncontact phases, and controller design requirements are developed to achieve maximum decoupling. Design requirements involve output subspace of each controller leading to control discontinuities for contact and noncontact phases. In the noncontact phase, satisfaction of design requirements leads to a fully linearized and decoupled system. When in contact with the constraining surface, design requirements eliminate disturbances in the force loop, but minimize disturbances in the position loop to an extent dependent on force loop performance. Known hybrid control schemes analysis is performed to reveal existence of control loop interactions in these schemes. Confirmation of theoretical analysis is done through simulation of a three revolute planar manipulator. © 1998 John Wiley & Sons, Inc.

Objective: This study aimed to investigate whether the subjective assessments of strong and weak muscles in the Functional Myodiagnosis muscle test (FMD-MT) can be objectively and reproducibly verified using physically measurable parameters. Additionally, we sought to evaluate the reliability of the manual muscle test in order to reinforce the scientific evidence supporting this accepted, yet not widely adopted, complementary medicine method. Methods: In a crossover observational study, three experienced medical practitioners conducted the FMD-MT of the rectus femoris muscle on 24 healthy participants using a specially designed therapy bench, with all measurements recorded via an oscillogram. The study investigated the force-time integral, joint angle change, additional force load, mean force turning point 1, as well as the interrater reliability and validity of both examiner assessments and instrumental analyses for the two muscle reaction variants: strong and weak. Results: A significant difference between the response pattern of strong and weak muscles was identified for the force-time integral (p = 0.005), the change in joint angle (p < 0.001), and the additional force load (p = 0.001). No difference between strong and weak muscles could be detected regarding the force turning point 1 (p = 0.972). The examiners demonstrated 100% accuracy in identifying weak muscle reactions as weak, and 99.2% accuracy in identifying strong muscle reactions as strong (p = 0.316). The overall intra-class correlation coefficient was 0.984. The oscillogram correctly visualized weak muscle reactions in weak muscles with an accuracy of 81.7%, and strong muscle reactions in strong muscles with an accuracy of 86.7% (p = 0.289). Conclusions: The Functional Myodiagnosis muscle test (FMD-MT) enables a clear and objective differentiation between strong and weak muscles, with statistically significant differences observed in the force-time integral, additional force load, and joint angle changes. Under rigorously standardized testing conditions, the FMD-MT of the rectus femoris muscle demonstrates a validity rate of 99.6% and an excellent reliability (ICC 0.984). Consequently, the FMD muscle test proves to be a reliable, reproducible, and objective diagnostic method. Trial registration: German Register of Clinical Studies U1111-1212-6622.

Bony fish swim with a level of agility that is unmatched in human-developed systems. This is due, in part, to the ability of the fish to carefully control hydrodynamic forces through the active modulation of the fins' kinematics and mechanical properties. To better understand how fish produce and control forces, biorobotic models of the bluegill sunfish's (Lepomis macrochirus) caudal fin and pectoral fins were developed. The designs of these systems were based on detailed analyses of the anatomy, kinematics, and hydrodynamics of the biological fins. The fin models have been used to investigate how fin kinematics and the mechanical properties of the fin-rays influence propulsive forces and to explore kinematic patterns that were inspired by biological motions but that were not explicitly performed by the fish. Results from studies conducted with the fin models indicate that subtle changes to the kinematics and mechanical properties of fin rays can significantly impact the magnitude, direction, and time course of the 3D forces used for propulsion and maneuvers. The magnitude of the force tends to scale with the fin's stiffness, but the direction of the force is not invariant, and this causes disproportional changes in the magnitude of the thrust, lift, and lateral components of force. Results from these studies shed light on the multiple strategies that are available to the fish to modulate fin forces.

This paper proposes a hybrid force/position controller for industrial robotic manipulator based on Kalman filter. Firstly, the mathematical model of real contact force is built to estimate the actual contact force by applying Kalman filter using a force derivative to achieve the system state description. The estimated actual contact force is used to control the end-effector force as well as estimating the stiffness of environment. To refine the environment stiffness estimation the Recursive Least Square (RLS) technique has been employed. Owing to the fact that the general industrial manipulator only provides the position control mode, the position-based hybrid force/position control architecture is designed and realized by using the position tracking mode of the motion control card. The main advantages of the implemented controller is simplicity, computational efficiency and robustness to unknown environment, it is convenience for the general industrial manipulators. Besides, it lends itself for industrial manipulators in order to achieve compliant behavior and perform complex tasks. The proposed control structure is successfully validated by practical experiments. The results show that the controller has a satisfactory performance in term of force control and trajectory tracking and robustness to force/torque sensor measurement interferences.

In order to achieve the desired control of a lower limb exoskeleton, an understanding of the dynamics of the coupled human-exoskeleton system is required. A major input towards modelling the dynamics of the coupled system is the ground reaction force (GRF) generated by the human wearing the exoskeleton. Therefore, the GRF from the coupled system needs to be either computed, measured or estimated. This paper presents work on the estimation of GRF and subsequently on the control of a lower-limb exoskeleton. The approach to estimating GRF is based on the multiple variable regression technique, which considers the body weight, height and walking speed of the exoskeleton user. A mathematical model based on the Euler-Lagrange formulation was used to model the complete system. Once the dynamic model is ready, strength augmentation for the purpose of load-carrying exoskeletons is set as a desired control objective, and further computed torque control is tested on the coupled system. In summary, this paper tries to achieve three goals: estimation of GRF, dynamic modelling of the coupled human-exoskeleton system and formulation of a control framework from the modelled dynamics for testing computed-torque control.

In previous work, a position-based force control was established using two-axis load cell buttons embedded into a 7-DOF three-fingered robot hand. However, the inconsistent readings of the incurred force which is due to the loose placement of the movable parts of the fingertip has led to the motivation to replace the sensor. This paper discusses the application of a new 6-axis force sensor for the robot hand impedance control. The objectives of this work are to establish a new interface and to modify the existing impedance control of the robot hand according to the application of the new 6-axis FT sensor and interfaces. The interface between the hardware, sensors, and controller within the robot system was implemented on the Simulink Matlab application. The inputs and outputs of two different Peripheral Component Interconnect (PCI), which are PCI NI-6225 and PCI ADVANTECH-1771 were configured and verified through experiment. It can be observed that the new interface was feasible by using multiple PCIs. Meanwhile, the impedance control results showed that the position reference changed accordingly when the exerted force exceeds the threshold force based on the measurement from the new sensor.

The paper presents a sensorless direct force (DFC) control method for a surface permanent magnet linear synchronous motor (SPMLSM) drive that provides high-performance speed control without position and speed sensors. To solve the practical problem of sensorless propulsion, DFC method is selected to control the thrust force and stator flux linkage of SPMLSM. The sensorless control scheme is based on the measurement and observation of stator current, voltage, and flux vector. Two phase voltages and two stator currents are measured and processed. The rotor speed is estimated through the stator flux and its derivative estimation. Flux and its derivative are calculated in the stationary reference frame and used to estimate the speed. In this paper a DFC based on fuzzy logic is adopted, so that the proper stator voltage vectors can be selected according to the force error. To test the control strategy a simulation using SIMULINK is built. The results show that the proposed control technique gives a good performance for tracking applications.