Coordinated compliant motion of two robotic devices can introduce greater flexibility and dexterity into manufacturing and improve productivity. By formulating coordinated compliant motion of two robotic devices as constrained motion of a manipulator under rheo-holonomic constraints imposed by a positioner, this paper studies dynamics and control of manipulators under rheo-holonomic constraints, which contain time explicitly. Two kinds of coordinated compliant motion: coordinated deburring/contour-following and coordinated peg-in-hole are discussed, and the redundancy resolution issue is also addressed. Finally, two and three dimensional coordinated deburring/contour-following are presented as illustrative examples.
A method for determinating the velocity disturbance equivalent to a torque disturbance for mechatronic servo systems including robot manipulators and machine tools is proposed. The equivalent velocity disturbance is determined by several typical experiments of actual load tests for the system. By using the equivalent velocity disturbance, we can obtain any load characteristics of the mechatronic servo system without use of actual loads.
Dynamic control of a three-fingered robot hand manipulating an object in three-dimensional space while allowing one of the three fingers to slide so that to change its grasp location on the object surface is formulated. The static and dynamic friction at the grasp point of the sliding finger on the object surface is considered explicitly and their effects to the finger and object behaviors are discussed. Motion equations of the whole system are derived and a dynamic control law for realizing the desired object motion as well as the desired finger sliding and the desired grasping force is proposed. The realizability of the given trajectories under the constraints of maximal static friction and dynamic friction at the grasp points, and of joint driving torque, are also discussed. A simulation example to demonstrate the use of the proposed control law is given. The results of this work will be useful for a multifingered robot hand in certain tasks to perform regrasping and reorientation of an object without breaking the grasping.
Recently, many wheeled robots with an ability to pass over rough roads and steps have been developed. However, the structures of such robots are generally very complicated with many degrees of freedom. Therefore, we have developed a four-wheeled robot which has the ability of passing over a step with simple structure. We call it a variable structure type four-wheeled robot. For the realization of stepping over, there are several difficult problems to be solved, such as control methods for state transfer and stabilization in 2-wheeled state. In this paper, we mainly discuss control methods for transfers from 4-to 2-wheeled state and from 2-to 4-wheeled state. Especially in the transfer from 4-to 2-wheeled state, we make effective use of the driving torque of body's motor. In the transfer from 2-to 4-wheeled state, we have investigated a control method for soft landing to minimize the touch-down impact of the robot. By combining our control methods, we have realized an experiment of passing over a step successfully.
A mechanism with more generalized coordinates than the number of actuators is said to be an underactuated mechanism. An open kinematic chain with unactuated joints lies in this category. The motion constraints of underactuated multi-link mechanisms are due to their dynamics and do not usually have even the first integral. Such nonholonomic systems are characterized by a nonlinear affine state equation with a drift term. In this paper, we discuss asymptotical stabilization and positioning control of a nonholonomic mechanism with drift.
A number of positioning identification techniques have been used for mobile robots. Dead reckoning is a popular method, but is not reliable when a robot travels long distance or over an uneven surface because of variations in wheel diameter and wheel slippage. The landmark method, which estimates the current position relative to landmarks, cannot be used in an uncharted environment. This paper proposes a new method called“Cooperative Positioning System (CPS) .”For CPS, we divide the robots into two groups, A and B. One group, say A, remains stationary and acts as a landmark while group B moves. The moving group B then stops and acts as a landmark for group A. This process is repeated until the target robot position is reached. CPS has a far lower accumulated positioning error than dead reckoning, and can work in three-dimensions which is not possible with dead reckoning. Also, this method has inherent landmarks and therefore works in uncharted environments. This paper gives the basic consideration on positioning accuracy of CPS, and reports the positioning experiments by the constructed robots with CPS.
In the sensor feedback control of intelligent robots, the delay time must be reduced for a large number of arithmetic operations. In addition to many multiply-additions, the arithmetic operations such as absolute value calculation and maximum value selection are often used in the dynamic control of robot manipulators. To reduce the delay time for multi-operand arithmetic operations, the architecture of the reconfigurable parallel processor is proposed. In each processor element, a switch circuit is used to change the connection between the multipliers, adders and arithmetic units (AUs), so that the multi-operand AUs having desired numbers of operands can be reconfigured. Since the data transfer is accomplished by the direct connection between the multipliers, adders and AUs, the overhead for data transfer is reduced. The chip evaluation based on 0.8 [μm] CMOS design rule shows that the delay time for differential inverse kinematics computation and inverse dynamics computation of a six-degrees-of freedom manipulator become 1.7 [μsec] and 11.5 [μsec], respectively.
A conventional floor polishing mobile vehicle or robot that has a rotary brush should be fairly large in body size and heavy in weight to prevent unnecessary movement caused by friction between a rotating brush and a floor. When those robots having lager weight are used to sweep or polish a floor, accidental collisions may damage office fixtures in a room. From this point of view, a light weight polishing robot is preferable. In this paper, we propose a new floor polishing robot moved with a new locomotion mechanism. Driving force for locomotion and steering of the robot is generated by a friction between a rotary brush and a floor with inclining the brush. This reaction force is calculated by the theoretical model in order to control the robot. Experimental results show the robot rotation angle is controlled within an error of 1 degree using PID control rules.
The new master-slave control method is proposed on multi-control modes for a master-slave manipulator with different configurations. A virtual internal model following control is applied to position symmetrical bilateral control. In our method, a master-slave control mode (MS-mode), a joystick control mode (JSmode), a master arm offset mode (OM-mode), and a servo hold mode (LK-mode) are able to be realized by operating the desired output values of the virtual internal models in a common control algorithm. There is compliant characteristic between the master and slave models. In the result of evaluation experiments between the MSmode and the JS-mode, although the MS-mode is superior to the JS-mode in manipulating a fine task, our JS-mode is found to be useful to carry out such a task compared with a conventional JS-mode which only directs the rates for the slave arm. In the JS mode, the slave arm moves to the position where the reaction force of the slave arm and the operating force of the master arm are balanced. Thus, it is possible either to control an overload for an object and to control the contact force. The validity of the proposed method is verified.
Robustness of grasps is defined such that the hand's mechanism can passively resist against bounded external forces without relying on the feedback control of joint torques. Power grasp is redefined as a grasp with robustness. Defective contacts were reported to play an important role in resisting external forces. By categorizing defective contacts into regular and singular defective contacts, we analyze the mechanism of robustness. A computational scheme is estab lished to calculate the critical external force, namely, an external force that can move the grasped object in a specified direction. The virtual work rate is proposed as the evaluation criterion of the robustness of grasp. The effectiveness of the computational scheme and the evaluation criterion are verified with an illustrating numerical example.
In order to reduce the uncertainty in assembly operations, it is effective to bring a part into contact with a fixed environment and guide it on the contacting planes into a designated position.This paper considers using robot fingers to manipulate a part in contact with a fixed environment to perform a planned assembly operation. We believe that assembly operations by robot fingers have much potential compared to those of conventional grippers in the sense of dexterity, preciseness and flexibility. However, in order to perform assembly operations by robot fingers, it is necessary to plan fingertip positions on the part to be manipulated. First, in this paper, the region of feasible fingertip force needed to balance the reaction force from the environment is explicitly represented to ensure that the part is manipulated stably, when the static and dynamic friction among the objects are considered. Next, considering the assembly operation quasi dynamically (i. e. the square term of the motion velocity is small enough to be neglected but its acceleration will be considered), the region of feasible fingertip force needed to manipulate the part to its designated direction is described. According to this region of feasible fingertip force, the corresponding feasible fingertip position range on the object surface can be obtained.
This paper proposes a dynamic control method to transfer a common object by the coordination of multiple wheeled mobile robots. The coupler which comprises an active prismatic joint and a passive rotary one is installed on each robot so that even the mobile robot with non-holonomy can correctly manipulate the object. The coordinative control system composed of a leader and other staff robots is designed to perform the accurate and high-speed object transportation based on the synchronous motions of the robots under their dynamical interactions. The leader robot successively defines the desired acceleration of the object to move along its target trajectory, and broadcasts the information to the staff robots. Each staff robot controls the motions of its own body and the on-board prismatic joint so as to achieve the desired acceleration of the object. When the prismatic joint approaches its mechanical limit, the staff robot requests to modify the desired acceleration of the object to the leader. The control algorithm is formulated on the basis of the kinematics and the dynamics of both the object and the robot. The simulation results for the transportation of an object by four mobile robots illustrate the validity of the proposed coordinative control method.