Experimental Study on Multi-mode Control and Cascade Control of Electrohydraulic Shaking Table with Actuation Redundancy

This paper describes an internal force sensor for a new redundant parallel manipulator. In convensional control methods of a redundant parallel manipulator, optimal torque minimized actuator torque or maximized manipulability by using evaluation function is decided and used. However, these methods have to use a torque controlled actuator. It's torque is small, also it is expensive. So, we proposed a new control method using a conventional geared actuator. In our method, internal forces produced by actuator redundancy was detected by an internal force sensor and controlled to be zero. This force sensor is designed to detect only internal forces loaded the end-effector. We demonstrate about the structure and the principle of the proposed internal force sensor, and experimental result of the internal force sensor when internal and outer forces are loaded it.

To address the demands for precision and load-bearing capacity in the installation of building panels, a hybrid force-position driven robot with redundant actuation has been developed. The mechanical performance of this robot is primarily governed by its central parallel mechanism, which is equipped with redundant actuators matching the degrees of freedom. Non-redundant and redundant actuators are respectively responsible for position and force control. The inclusion of redundant force-driven joints has increased the internal coupling within the mechanism. To enhance the coordination between position and force control, a hybrid synchronized control method based on cross-coupling has been proposed. Initially, kinematic and dynamic models of the parallel structure were established. Under predefined trajectories, the theoretical inputs for each actuator were calculated using inverse kinematics and dynamics. Subsequently, employing the principle of cross-coupling, the torque output from the position actuators was used as feedback. This feedback was processed by a synchronized coordination controller to adjust the output force of the redundant force-driven joints. By adjusting the output force of the redundant actuators, the torque burden on the position actuators was effectively reduced, thereby enhancing the precision of position control. Additionally, under the same load conditions, smaller power actuators could be utilized for position control, reducing the overall weight of the robot and improving its load-to-weight ratio. To validate the effectiveness of the proposed control strategy, a robotic simulation environment was established. The simulation results demonstrated significant reductions in the average torque required by the position actuators across three different trajectories, with reductions of 91.43%, 54.56%, and 80.6% respectively. Finally, the load-bearing capacity and the load-to-weight ratio of the prototype were assessed. Experimental results confirmed that the prototype achieved a load-to-weight ratio of 15.83%, validating the effectiveness of the hybrid synchronized control method based on cross-coupling.

With the development of ATO (Automatic Train Operation) system for heavy-haul trains, advanced control methods to ensure the safe and stable operation of the train have become an urgent demand. To this end, a cascade control method based on MPC-PI (model predictive control and proportional integral) control is proposed. A multi-particle dynamic model of heavy-haul trains is established, and then the model is linearized for control algorithm design. In this cascade control method, the outer loop adopts MPC with large sampling time, and the optimization objectives consist of in-train forces, energy consumption and speed tracking error. The MPC control is formulated as QP (Quadratic Programming) problem, the output of which is used as the initial input of the inner loop. The inner loop adopts PI control with small sampling time, and adjusts the actual train control output in real time for the speed tracking error. The simulation results of 20,000 tons heavy-haul train show that the proposed method has better robustness and anti-interference than MPC and PI control separately. The optimization objective function is formulated with weighted coupler force and energy consumption, and the simulation results are compared with different sets of weights, which prove the effectiveness of the proposed method.

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.

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.

Position control and vibration control of the underactuated flexible robot in operational space is implemented. Firstly, the dynamic equations in operational space are derived using the assumed modes method. And kinematics and dynamics of the system are analyzed. Secondly, position control method of the underactauted flexible manipulator in the operational space is proposed. Because the elastic vibration of flexible links can not be eliminated only via position control, based on position control strategy, vibration control schemes are presented. The simulation of a 2DOF underactuated flexible manipulator indicates that position and vibration control methods have great effects on increasing end manipulation accuracy, reducing tracking errors and improving dynamic characteristics, which also verifies the validity of control strategies. Thus, for the underactuated flexible robot, both the position control and the vibration control are implemented simultaneously.

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. >

This paper presents a multi-mode controller approach for a constrained linear system with bounded disturbances based on the model predictive control (MPC) framework. Compared with single MPC controller implementations, the proposed approach has the flexibility of having a large domain of attraction, good asymptotic behavior and reasonably low on-line computation. The closed-loop control law of the multi-mode controller is available in closed-form. In this case, the proposed controller has fewer partitions of the domain of attraction compared to single MPC controller having similar domain of attraction. The performances of the approach are presented via an example

Error Analysis of Matrix Control of Six Degree-of-freedom Electro-hydraulic Shaking Table

Based on the analogy of heat and wave equations, novel decentralized control methods of a redundant manipulator are proposed. Because these control methods are based on real physical phenomena, physical sense of control parameters can be understood intuitively. Some traditional control methods can be reconstructed from the viewpoint of proposed methods. Furthermore, stable characteristics of the heat conduction imply stability of the control method. As case studies, three subjects are discussed: position control of the end-effector of manipulator, obstacle avoidance, grasping behavior. Some numerical results are shown to illustrate capabilities of proposed control methods.

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.

Most advanced manufacturing processes require precise linear-position control for material transfer, packaging, assembly, and electrical wiring. To achieve precise linear motion, most of these high-performance manufacturing machines use X-Y sliding tables with permanent-magnet rotary motors and rotary-to-linear couplers. Though this method is the most widely used, it has disadvantages of low accuracy, complex mechanical adjustments, high cost, and low reliability. This paper describes the use of the variable-reluctance-driving principle to construct a novel linear direct-drive actuator system for high-performance position control in manufacturing automation. The proposed actuator has a very simple structure and it can be manufactured easily. There is no need for magnets and no limitation on the traveling distance. The actuator is extremely robust and can be used in hostile environment. A novel control method, using cascade control and the force-linearization technique, is developed and implemented for precision position control of the actuator. Experimental results of the motion system indicate that the system has fast responses with good accuracy.

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.

In this paper we provide a review of the state of the art for active vibration control of axially moving materials (string and beam, etc.) in the past ten years, with particular regard to the subjects of some important active control methods of axially moving strings. First, an introduction is given to explain the aims and scope of this paper. This is followed by a comprehensive discussion of the active wave control methods presented by many investigators in the past ten years, including feedback control methods (such as the modal control method, the direct velocity feedback control method and the control method via transfer function formulation), active wave control methods combining transfer function, boundary control methods using the Lyapunov function, the variable structure control method, the adaptive control method, the vibration control of an axially moving beam and the active control of a moving material with arbitrarily varying length, etc. Finally, we conclude with a discussion of several issues for future research in this area.

This study mainly focuses on the synchronization problems of whole-body CT scanner. A master-slave synchronous control method is used to achieve synchronism between the gantry rotation motor and the bed moving motor in helical scanning mode, while the cascade control method is used to enhance the stability of each motor. In order to keep synchronous control, a control law is designed by the eigenstructure assignment method, which insures the accuracy of the signal tracking of the periodic load disturbance during the dual-motor synchronous control, and eliminates the adverse effects brought by periodic load. The proposed algorithm is simulated on MATLAB, and compared with the traditional PID algorithm. In addition, the algorithm is implemented on ARM9 and evaluated on a realistic synchronization control experimental platform designed by us. Both the simulation and realistic experimental results indicate that the algorithm is feasible for helical scanning.