An Internal Force Sensor for Control of a Redundant Parallel Manipulator

The electrohydraulic shaking table with actuation redundancy is widely used in the field of structural seismic and geohazard testing and research. To achieve more precise control of it, additional methods are required to suppress the internal force between actuators, building upon the six-degree of freedom (DOF) position control. This paper presents an analysis of two control methods: multi-mode control and cascade control. The high-performance electrohydraulic shaking table, equipped with eight actuators, serves as a case study. The multi-mode control approach introduces two distorted modes of the table to obtain a definitive solution for the actuator’s drive signals. By incorporating these modes, the internal force between actuators can be effectively mitigated. On the other hand, the cascade control method achieves control over the actuators’ force by incorporating eight inner loop force controllers. This approach has also proven effective in reducing the internal force between actuators. Analysis and experimental results demonstrate the efficacy of both methods in mitigating the internal force between actuators. Moreover, the cascade control method exhibits versatility and is not restricted by the number of actuators, making it a suitable choice for systems with more than eight actuators.

This paper presents analysis on kinematics and statics of redundant serial link manipulator and redundant parallel link manipulator with passive joints. Passive joint is a joint that the joint torque depends on the joint angle. Redundant manipulator is a manipulator that has actuated joints more than dimension of the task space. We study the theme not to be defined well the fundamental theory of the manipulator with passive joints. First, we study the redundant serial link manipulator with passive joints. We propose a solution method of kinematics and statics and a control method in a limited condition. Moreover, we can show a better performance of the serial link manipulator with additional passive joint, so-called semi-active joint, if we can control the equilibrium positions of passive joints by using numerical example. Secondary, we study the redundant parallel link manipulator with passive joints. We proposed a solution method of kinematics and statics. We can show the performance in each parallel link manipulator mode with semi-active joints by using numerical example.

This paper deals with the performance analysis of a 3-degree-of-freedom (3-DOF) planar parallel manipulator with actuation redundancy. Closed-form solutions are developed for both the inverse and direct kinematics about the redundant parallel manipulator. In performance analysis phase, the dexterity is analyzed, three kinds of singularities are investigated, and the stiffness is estimated. Compared with the corresponding non-redundant parallel manipulator with the redundant link removed, the redundantly actuated one has better dexterity, litter singular configurations and higher stiffness. The redundantly actuated parallel manipulator was applied to the design of a 4-DOF hybrid machine tool which also includes a feed worktable to demonstrate its applicability.

This article presents a model predictive control (MPC) method for humanoid dual-arm robots (DARs) to realize hybrid force-velocity control in the task space. The proposed method, named hybrid force-velocity MPC (HFV-MPC), enables simultaneous tracking of velocity and external force in the task space, as well as internal force regulation. First, a synchronous decoupling model of internal force, external force, and velocity is developed to address the limitations of conventional methods that decouple internal and external forces solely in the end-effector space and fail to meet the independent regulation requirements of external force and velocity in the task space. Furthermore, a generalized velocity model that integrates task-space velocity, external force, and internal force was established, and a HFV-MPC framework is constructed to enhance system robustness and achieve precise dual-arm force–velocity tracking. Subsequently, a comprehensive MPC cost function is designed, incorporating a dual-arm motion coordination coefficient to suppress undesired redundant joint motions and improve whole-body motion stability. In addition, a feedforward-linearized incremental system is derived, where the incremental model and force prediction jointly construct a generalized state-space model for MPC, to balance modeling accuracy and computational efficiency. Finally, the proposed method is validated in terms of effectiveness and robustness through both simulation and physical robotic experiments.

SUMMARYThe evaluation of joint velocity, torque, and power capability of the 8-PSS redundant parallel manipulator is investigated in this paper. A series of new joint capability indices with obvious physical meanings are presented. The torque index used to evaluate the respective joint dynamic capability of the redundant parallel manipulator is decoupled into the acceleration, velocity, and gravity term. With these velocity, torque, and power indices, it is possible to control the respective joint capability of the redundant parallel manipulator in different directions. The indices have been applied to evaluate the joint capability of the redundant parallel manipulator by simulation. They are general and can be used for other types of parallel manipulators.

In a musculoskeletal system, internal tensile forces are generated among the muscles because it is a redundant system. The balancing of the internal tensile forces for a given posture generates a potential field in the system. Therefore, the potential field is utilized for the sensorless feedforward position control and improvement of stability based on the feedback method. However, the stability of the internal tensile forces is strongly influenced by the muscular arrangement. Previous studies showed that a stable condition can be identified through the minimization of the potential at a desired posture, and the sufficient condition has been theoretically established; however, the geometric condition of the muscular arrangement has not been determined. To effectively exploit the characteristics of the internal tensile forces, the geometric condition must be elucidated in the design of a musculoskeletal system. This paper aims to clarify the geometric condition to generate stable internal tensile forces. Based on the conditions generating the potential that is minimum at the desired posture, the paper analyzes that the geometric condition on a musculoskeletal structure with two-link and six-muscle. Additionally, the identified condition is assessed based on simulations. As a result, we revealed the geometric condition of the muscular arrangement to generate stable internal tensile forces. By designing the muscular arrangement to satisfy the condition, the stability of the internal tensile forces is ensured, and consequently, a control method utilizing the characteristics of the internal tensile force is stably implemented.

The secondary internal force caused by temperature in statically indeterminate bridges are usually huge, sometime is the control factor in bridge design. Since the temperature investigation of bridge construction site is difficult to predict, there deviation between design joining temperature and actual temperature and the leaded secondary internal force is inevitable. Based on this, an adaptive temperature internal force control method is proposed. This method utilizes a pre-set steel cable. When the environmental temperature changes produce negative effects to the structure, the additional force and moment of cable with the change of environment temperature will offset the effect. This method can be widely used in the temperature internal force control of statically indeterminate bridge structures, and can effectively reduce the additional internal force of undetermined bridge structures caused by temperature differences.

When a mechanism is overconstrained it leads to the generation of internal forces. These forces do no work but have an effect on the apparent structural stiffness of the mechanisms. The degree of this effect depends on the magnitude or the mode of the internal forces and the geometry of the mechanisms. Internal forces may result from external or gravitational forces or the inertial loads during motion. If a mechanism has a closed chain structure, the redundant actuation may generate internal forces as well. -. . 'o The authors analyse the apparent structural stiffness of the closed mechanisms due to redundant actuation and the forces arising during dynamic motion. >

Oil-injected twin-screw compressors are widely employed in many commercial and industrial applications because of their high efficiency and reliability. Although extensive literature on modeling techniques applied to twin-screw machines exists, researchers are continuously developing models to capture advanced physical phenomena occurring during the compression process (e.g., mass and heat transfer mechanisms). In order to generalize the concept of mechanistic compressor modeling, a framework for the simulation of positive displacement compressors and expanders (PDSim) has been developed and validated by the authors. The platform has been utilized to model a number of compressor types including scroll, reciprocating, linear, single-screw, rolling-piston, Z, and spool. In this work, the simulation tool has been extended to include twin-screw machines. Beside the detailed geometry model needed to obtain volume curves of the working chambers, sealing lines, and rotor surface areas, three main aspects have been enhanced with respect to the existing literature: (i) a two-fluid (refrigerant and lubricant oil) chamber model with mass and heat transfer interactions; (ii) computation of gas forces, loads on the bearings, and hydrodynamic bearing sub-models; (iii) detailed overall energy balance with a multi-lumped temperature thermal network and a discharge gas pulsations post-processing model. A 4/6 oil-injected twin-screw compressor has been considered to conduct experimental analyses with internal pressure and force sensors, modeling and validation as well as sensitivity analyses.

Three-dimensional vortex-induced vibration analysis of catenary-type risers under flow with different incident angles

This paper describes a method of fault diagnosis of internal and external sensors for mobile robot. As our previous works diagnosed hard and noise faults of internal sensors, in this paper, scale faults, in which sensor gains deviate from the fault-free condition, are handled for three internal sensors (two wheel-resolvers and one gyro). The sensor gains are estimated based on the robot velocity estimated with a fault-free external sensor (a forward-looking laser range sensor) via the scan matching method, and then the scale faults are diagnosed. Abrupt faults of the external sensor are handled in this paper. They are detected based on errors related to the scan matching; if the laser images in several successive scans are not matched, the external sensor is decided to be faulty. False detection of the external sensor faults in dynamical environments is improved based on the occupancy grid method. Experimental results in an indoor environment show the performance of our method.

The interaction force control problem for the object manipulated by the dual-arm manipulator with the unknown environment is addressed in this paper. An adaptive dual-loop impedance control scheme is designed to meet the three control targets, including the trajectory tracking control of the object, the internal force control of the object with the two arms, and the interaction force control of the object with the unknown environment. Firstly, an adaptive variable impedance control method is proposed in the outer loop to copy with the unknown stiffness and position of the environment. Secondly, an impedance control scheme based on the internal force is designed in the inner loop to plan the internal force and the modified position supplied with the outer-loop control. Thirdly, to realize the reference trajectory supplied with the inner-loop control, the virtual decomposition control (VDC) method is incorporated, which is a recursive adaptive control progress, so that the unknown dynamics of the manipulators is acceptable and the computation complexity is also very low to satisfy the real-time control requirement. The stability verifications of the inner-loop impedance control and the VDC method are given based on the Lyapunov method, and the stability analysis of the outer-loop impedance control is obtained using the Routh criterion. Finally, a plane dual-arm robotic manipulator with three degrees of freedom is used to verify the effectiveness of the proposed control scheme.

SUMMARYParallel kinematics machines (PKMs) can exhibit kinematics as well as actuation redundancy. While the meaning of kinematic redundancy has been already clarified for serial manipulators, actuation redundancy, which is only possible in PKMs, is differently classified in the literature. In this paper a consistent terminology for general redundant PKM is proposed. A kinematic model is introduced with the configuration space (c-space) as central part. The notion of kinematic redundancy is recalled for PKM. C-space, output, and input singularities are distinguished. The significance of the c-space geometry is emphasized, and it is pointed out geometrically that input singularities can be avoided by redundant actuation schemes. In order to distinguish different actuation schemes of PKM, a nonlinear control system is introduced whose dynamics evolves on c-space. The degree of actuation (DOA) is introduced as the number of independent control vector fields, and PKMs are classified as full-actuated and underactuated machines. Relating this DOA to degree of freedom allows to classify the actuation redundancy.

Kinematic redundancy and actuation redundancy contribute to the increased functionality and reliability of multi-degree-of-freedom (DOF) robot manipulators. The former refers to having more kinematic DOF than required for a given task, whereas the latter indicates having more actuators than required by the kinematic DOF of the mechanism. Combining these types of redundancy introduces rich functionality into mechanical systems; however, integrated control methods have not been sufficiently studied. This paper addresses solving these redundancies and proposes a control method for mechanical systems with both types of redundancy. Modal system design based on the statics of robot manipulators was adopted to solve actuation redundancy, and kinematic redundancy was treated separately. The proposed methodology was validated through experiments using a planar 3-DOF parallel robot with four actuators under hybrid position/force control.

The objective of this paper is to determine whether a planar parallel manipulator with redundant actuation has better tracking accuracy than a planar parallel manipulator without redundant actuation. The effects of the redundant actuation on tracking accuracy of parallel manipulators are studied by using two different experimental platforms. The first platform is the planar five-bar parallel manipulator with normal actuation, and the other one is the planar parallel manipulator with redundant actuation. The dexterity pictures and the kinematic configurations of the two platforms validate the kinematic advantages from the redundant actuation. In order to study the dynamic advantages of the redundant actuation further, a nonlinear adaptive controller is presented for the two platforms. The experimental comparison is implemented on two actual parallel manipulator platforms, and from the experimental results, one can find the tracking accuracy of the parallel manipulator with redundant actuation can be improved above 38% than that of the five-bar parallel manipulator without redundant actuation.