Remote Center Compliance Research Articles

Development of 6 DOF Displacement Sensor Using RUS Parallel Mechanism.

Nowadays, many types of manipulators have been developed and used in lots of production processes. Force-based control methods or additional mechanical devices called Remote Center Compliance (RCC) have increased the system’s compliance and accuracy. However, the force-based control method’s operating speed is low, and the RCC cannot measure deflection. Thus it cannot calculate the position of the end-effector accurately. For accurate force and position control, it is necessary to measure the deflection of the RCC and to perform this, a different type of device than the existing RCC is required. This paper presents the necessity and possibility of developing an RCC capable of measuring the displacement of the end-effector and showing the displacement sensor’s feasibility using a 6 DOF parallel mechanism. In particular, we suggest that it is possible to make devices cheaper and more compact by using angular displacement sensors. Finally, we show the possibility of use in actual industrial sites through peg-in-hole simulation using the device.

Displacement Sensor Integrated Into a Remote Center Compliance Device for a Robotic Assembly

Compliance devices facilitate robotic assemblies by preventing excessive contact force on automated devices. However, the unavailability of displacement information regarding compliance devices makes it difficult to protect robots and objects during robotic assembly. It also limits repeatability and efficiency, especially regarding peg-in-hole and similar operations. We propose a six-axis displacement sensor installed on a remote center compliance device to detect the three translation and three rotation components generated by external forces and torques applied to the device, respectively. Triangular prism-shaped structures are used with capacitive sensing technology to measure the vertical and horizontal displacements in mm scale generated by the external normal and shear forces applied to the sensor. We designed and fabricated the sensor that could be integrated into a remote center compliance device, demonstrating it has a simple structure and is easy to install. To obtain six-axis force/torque information and six-axis displacement, calibration experiments were conducted using a specific setup and considering the device's geometry. The high sensing performance was verified through complementary experiments.

Precision Assembly of Heavy Objects Suspended With Multiple Cables From a Crane

A new approach to precision mating of heavy objects suspended from overhead cranes is presented. We have found through experiments that heavy shafts suspended with multiple cables at specific positions and orientations can be inserted into a chamfered hole despite a small clearance. This will allow an overhead crane, although limited in positioning accuracy, to execute precision assembly of a heavy shaft simply by holding it with multiple cables and lowering it onto the chamfered hole of a fixed object. Unlike the well-known Remote Center Compliance (RCC) hand, this method does not use a two-layer elastic structure but exploits the physical properties of cables. Specifically, cables go slack when a compressive load is applied. This unidirectional load bearing property is exploited to suspend a heavy shaft such that it is not over-constrained during insertion. Conditions for the cable attachment position and orientation for successful insertion are obtained. A proof-of-concept prototype is developed and experimental verification of the principle and analysis are presented.

Contact force detection and control for robotic polishing based on joint torque sensors

In robotic polishing applications, the rotating polisher will generate strong vibration disturbance, which makes it more difficult to detect and control the contact force. This paper proposes a novel and practical method to detect and control the contact force using the built-in sensors (motor encoders and joint torque sensors) for actual robotic polishing in harsh conditions of strong vibration disturbance. An extended state observer based on the robot dynamic model is developed to estimate the contact force in real time, and a new and efficient adaptive filter combining insights of the notch filter with the tracking differentiator is designed to relieve the strong vibration disturbance of torque signals from the eccentrically rotating polisher. On the basis of efficient force detection, a hybrid position/force control method based on the inner joint torque controller is proposed to realize accurate force control in actual robotic polishing of curved surfaces. With the proposed contact force detection and control methodology, the robot is potential to achieve satisfied polishing applications in which some usual accessories, such as the six-axis force/torque sensor or Remote Center Compliance device are absent. Experimental results confirm the effectiveness and accuracy of the proposed contact force detection method in conditions of strong vibration disturbance from the rotating polisher. In addition, the curved surface polishing experiments indicate that the new hybrid position/force control framework performs well on rejecting the strong disturbances while maintaining high force control accuracy of polishing, and the quality of polished surface is greatly improved.

A Flexibly Grasping and Manipulating Mechanism Composed of Many Elastic Cords

The authors have proposed a flexibly grasping and manipulating mechanism composed of two circular rings and many elastic cords between the rings. Aiming to control posture of the grasped object and to give the mechanism a remote center compliance ability, the mechanism is improved so that the relative translation between two rings can be given. A new numerical method to iteratively calculate the posture of a grasped object due to relative angular and translational displacements between the rings is established based on the equilibrium of force and moment applied by elastic cords. A prototype with a planar parallel mechanism with 2 DOF to give a pure relative translational motion between rings is built and experimentally examined. The prototype mounted on a spatial serial robot arm can grasp a cylinder and insert it into a circular hole in inclined surface by utilizing posture control and remote center compliance.

The Effect of Remote Center Compliance Parameters on Formation Control of Cooperative Wheeled Mobile Robots for Object Manipulation

Formation control is a potential advanced technology for aircrafts, spacecrafts and space robots. This paper, for the first time, studies several methods of passive and semi-active Remote Center Compliance (RCC) in order to examine their effects on formation control of a group of Wheeled Mobile Robots (WMRs) for object manipulation during space/terrestrial explorations. To this end, first, the dynamics model of the constrained non-holonomic robots, object and RCC system have been derived precisely. A leader-follower control strategy is then utilized for trajectory tracking of the desired path by the cooperative robots. Finally, the passive and semi active RCC are optimized to make the formation robust in the presence of significant disturbances. The results obtained reveal that the semi-active RCC system, combined with a PID controller, reduces the effect of the disturbances experienced as compared to the other passive RCC modules.

Passive compliant module with the displacement measurement sensor and its application for automatic assembly

Abstract Robot manipulators have been applied in the various automated manufacturing for handling, transferring, welding, polishing, painting, deburring, simple assembly and so on. Robotic assembly of the precision parts is difficult because the accuracy of the robot manipulator is not enough and the teaching procedure is complex. There have been various technologies about robotic assembly such as the position based assembly strategy, the active torque feedback control algorithm with FT sensor or joint torque sensors and the remote center compliance which gives the passive compliance to the end-effector. In the paper, we proposed a new type of the passive compliant device which can measure its deformation. The proposed device, which is called “Magic Gripper”, is composed of the passive compliance module, the gripping module, the displacement measurement module and the controller module. Also, a new assembly strategy using the passive compliant device with the displacement measurement system is proposed. The proposed device and the proposed assembly strategy are proved to be very useful for automatic assembly of the precision parts.

Modeling and Analysis of a Compliance Model and Rotational Precision for a Class of Remote Center Compliance Mechanisms

The remote center compliance (RCC) mechanism is of great use for practical designs, especially if a pure rotation about a virtual point is required. The analysis of compliance properties and rotational precision for RCC mechanisms are very important for mechanical design in applications where precision is required. This paper formulates an analytical method for the compliance and rotational precision calculations of a class of RCC mechanisms, combined in parallel with two round beam-based isosceles-trapezoidal flexural pivots. The analytical model of the mechanism is established based on the stiffness matrix method to directly obtain the compliance factors that completely define the elastic response of the mechanism. The rotational precision of the mechanism—That is, the position of rotation center—Is then derived using screw theory and a compliance matrix. The validity of this model is demonstrated using finite element analysis simulation and experimental tests. The results of both simulation and experiment verify that the analytical model has high accuracy and promising practical applications. Moreover, the influences of the geometry parameters on the compliance factors and the center shifts are also graphically evaluated and discussed using the analytical model. The results in this paper provide an effective configuration and analytical method for the design and optimization of RCC mechanisms, and are of great practical significance.

Multiple Impedance Control for object manipulation by a dual arm underwater vehicle–manipulator system

In this paper, control of an object manipulation task by a dual arm underwater vehicle–manipulator system (UVMS) is studied. The object is a heavy cylinder which should be moved and pegged precisely in an underwater structure while impacts due to contact are inevitable. The Multiple Impedance Control (MIC) is customized for this system, and the obtained results are compared with those of the augmented object model (AOM) approach. To this end, first an explicit dynamics model of the UVMS is developed. Hydrodynamic effects, i.e. added mass, drag and buoyancy are considered as external forces/moments in the task space, which are incorporated into the model by corresponding Jacobian matrices of their application points. Then, this derived model is used for preparing a MATLAB code by which the manipulation task in the 3D space is simulated. Extensive computer simulations show that in the presence of flexibility in the system that is modeled by remote center compliance the AOM does not have a stable performance, while the MIC yields a reliable performance. It is shown that even in case of appearing an impact due to contact with the environment, also severe model uncertainties, the system exhibits a smooth and nondestructive reaction.

Shear Control of Elastomer Shear Pads for Variable Remote Center Compliance

Research is performed to design a new variable remote center compliance (VRCC) device with elastomer shear pads (ESP) for robot assembly. The proposed ESP VRCC has a shear controller that can change the fixed point on the top side of the ESP which is attached to the upper plate of the VRCC while the bottom side remains fixed. In this case, the ESP is under shear stress, while the axial/lateral stiffness of the ESP changes according to the amount of shear stress. Therefore, the position of the compliance center can be controlled with the shear controller because the axial/lateral stiffness of the ESP is one of the design parameters that determines the position of the compliance on the ESP VRCC. To verify the effectiveness of the proposed design, the stiffness variation of the ESP and the position of the compliance center of the new VRCC are measured at various shear stresses.

ESP의 전단 변형을 이용한 원격 순응 중심 장치의 순응 중심 조절 방법에 관한 실험적 고찰

In this paper, an experimental study is performed to adjust position of compliance center of Elastomer Shear Pad Remote Center Compliance (ESP RCC) device, which is used on precise peg in hole process. In the study, variation of the lateral/axial stiffness of the ESP is proposed as a control parameter to adjust the position of compliance center of the ESP RCC. The variation of the stiffness of the ESP is achieved by controlling the shear stress of the ESP. To control the shear stress of the ESP, position of top side of the ESP is changed while remaining bottom side of the ESP is fixed on the RCC plate. To evaluate effect of the proposed idea, stiffness variations of the ESP on various shear stresses are measured, and variation of the compliance center is measured with the ESP RCC that can control the position of compliance center by using the shear stress. The measured data shows unique characteristics that have not been shown in other types of ESP VRCCs.

탄성 조절 막대를 이용한 가변형 원격 순응 중심 장치 개발에 관한 연구

In this paper, a simple idea is proposed to change the compliance center of the Remote Center Compliance (RCC) by adjusting the elasticity of the Elastomer Shear Pad (ESP). To vary the elasticity of the ESP, a hole is made in the ESP along its stiffness axis, and a stiffness adjusting rod (SAR) is inserted into the hole. By adjusting the insertion depth of the rod, lateral stiffness of the ESP can be varied, and the compliance center of the VRCC can be controlled accordingly. To verify the effectiveness of the proposed idea, a prototype VRCC is designed and, the position of the compliance center with various lengths of the inserted rod are measured.

Micro parts assembly system with micro gripper and RCC unit

This paper presents a new micro assembly system, which is composed of a micro gripper, a micro remote center compliance (RCC) unit, a voice coil motor-driving mechanism and precision motion stages. The micro gripper is actuated by two shape memory alloy (SMA) wires, and its grip is 1 mm. The micro RCC unit has low translational and rotational stiffness sufficient for micro parts assembly. The voice coil motor-driving mechanism can generate linear motion with an adjustable stiffness, and it can also measure external force in the moving direction. An algorithm for the automatic assembly of micro parts is also proposed, and assembly experiments are performed.

Development of a New Variable Remote Center Compliance (VRCC) With Modified Elastomer Shear Pad (ESP) for Robot Assembly

In this paper, a noble variable remote center compliance (VRCC) is developed. The VRCC has a simple structure to change the position of compliance center and to lock the VRCC. The VRCC consists of a top plate, a bottom plate and two modified elastomer shear pads (ESP). The modified ESP has a hole in its stiffness axis, and a stiffness adjusting rod (SAR) is inserted into the hole of the ESP. The stiffness of the modified ESP can be adjusted according to the insertion depth of the SAR so that the compliance center of the VRCC, which depends on the stiffness of the ESP, can be adjusted freely. Furthermore, by passing the SAR through the modified ESP, the VRCC can be locked easily. To verify the effectiveness of the proposed VRCC, a prototype VRCC is made and the variation of the compliance center is measured according to the insertion depth of the SAR. Note to Practitioners-This paper was motivated to reduce the number of machine tools which were used in connecting electric plugs in factory. But, this work is also applied to assembly machines which require inserting a round peg into a round hole. The existing machine tool can connect only one electric peg with fixed length, so various machine tools are needed according to the lengths of plugs. The proposed idea shows the way to solve this problem. By extending working capacity of the machine tool, it is possible that electric plugs with various lengths are connected by one machine tool and, consequently, the changing time and cost of machine tools can be reduced. The developed method removes changing of the machine tool. However, manual adjustment of the proposed machine tool is still needed to connect electric plugs with various lengths. Therefore, in the future research, motorized adjusting structure will be added to the proposed idea to improve manual adjustment of the machine tool.

Insertion of Long Peg into Tandem Shallow Hole Using Search Trajectory Generation

In this paper, we propose a method to insert a long peg into a tandem shallow hole using search trajectory generation without force feedback. The use of RCC (Remote Center Compliance) is a possible solution for robotic assembly, but it is no longer useful when the remote center cannot be set correctly. We focus a task to insert a peg into the tandem shallow hole as an example that cannot be accomplished by robots using RCC devices. For this task, firstly, a new peg insertion method using search trajectory generation is proposed to continuously adjust the peg position. Secondly, a floating unit is made in order to reduce the number of positions to be corrected. And then, a method to estimate an indication of the insertion axis and a method to revise the inclination in order to avoid a jamming phenomenon are also proposed. Finally, the effectiveness of these methods is verified by an experiment.

A three translational DoFs parallel cube-manipulator

This paper concerns the presentation and analysis of a type of three translational degrees of freedom (DoFs) parallel cube-manipulator. The parallel manipulators are the topology architectures of the DELTA robot and Tsai's manipulator, respectively, which have three translational DoFs. In the design, the three actuators are arranged according to the Cartesian coordinate system, which means that the actuating directions are normal to each other, and the joints connecting to the moving platform are located on three sides of a cube, for such reason we call this type of manipulator the parallel cube-manipulator. The kinematics problems, singularity, workspace, compliance characteristic of the manipulator are investigated in the paper. The analysis results show that the manipulators have the advantages of no singularities in the workspace, relatively more simple forward kinematics, and existence of a compliance center. The parallel cube-manipulator can be applied to the fields of micro-motion manipulators, remote center compliance (RCC) devices, assembly, and so on.

Development of Compliance Hands on Assembly Works. 2nd Report. Characteristic Performances of Working Load on Peg-in-Hole Task through Compliance Hands with RCC Devices.

For a peg-in-hole task in order to achieve more quickly and automatically interpositioning the objects we have developed such kind of remote center compliance devices as the spring and rubber mechanisms cooperating with the feedback systems by sensing load on the manipulator hands. We have evaluated the experimental performances of the friction forces, the friction coefficent and the effectiveness for the size of chamfers in respect to the clearances between pin and hole through the compliance robot hands. These test results have been evaluated to derive a criterion of the spring stiffness of RCC devices in practical uses.

Introduction to robotics analysis, systems, applications

Most chapter begins with an Introduction and conclude with a Summary, References and Problems. 1. Fundamentals. What is a Robot? Classification of Robots. What is Robotics? History of Robotics. Advantages and Disadvantages of Robots. Robot Components. Robot Degrees of Freedom. Robot Joints. Robot Coordinates. Robot Reference Frames. Programming Modes. Robot Characteristics. Robot Workspace. Robot Languages. Robot Applications. Other Robots and Applications. Social Issues. 2. Robot Kinematics: Position Analysis. Robots as Mechanisms. Matrix Representation. Homogeneous Transformation Matrices. Representation of Transformations. Inverse of Transformation Matrices. Forward and Inverse Kinematics of Robots. Denavit-Hartenberg Representation of Forward Kinematic Equations of Robots. The Inverse Kinematic Solution of Robots. Inverse Kinematic Programming of Robots. Degeneracy and Dexterity. The Fundamental Problem with the Denavit-Hartenberg Representation. Design Project 1: A Three-Degree-of-Freedom Robot. 3. Differential Motions and Velocities. Differential Relationships. Jacobian. Differential Motions of a Frame. Interpretation of the Differential Change. Differential Changes Between Frames. Differential Motions of a Robot and Its Hand Frame. Calculation of the Jacobian. How to Relate the Jacobian and the Differential Operator. Inverse Jacobian. Design Project. 4. Dynamic Analysis and Forces. Lagrangian Mechanics: A Short Overview. Effective Moments of Inertia. Dynamic Equations for Multiple-Degree-of-Freedom Robots. Static Force Analysis of Robots. Transformation of Forces and Moments Between Coordinate Frames. Design Project. 5. Trajectory Planning. Path vs. Trajectory. Joint-Space vs. Cartesian-Space Descriptions. Basics of Trajectory Planning. Joint-Space Trajectory Planning. Cartesian-Space Trajectories. Continuous Trajectory Recording. Design Project. 6. Actuators. Characteristics of Actuating Systems. Comparison of Actuating Systems. Hydraulic Devices. Pneumatic Devices. Electric Motors. Microprocessor Control of Electric Motors. Magnetostrictive Actuators. Shape-Memory Type Metals. Speed Reduction. Design Project 1. Design Project 2. 7. Sensors. Sensor Characteristics. Position Sensors. Velocity Sensors. Acceleration Sensors. Force and Pressure Sensors. Torque Sensors. Microswitches. Light and Infrared Sensors. Touch and Tactile Sensors. Proximity Sensors. Range-finders. Sniff Sensors. Vision Systems. Voice Recognition Devices. Voice Synthesizers. Remote Center Compliance (RCC) Device. Design Project. 8. Image Processing and Analysis with Vision Systems. Image Processing versus Image Analysis. Two- and Three-Dimensional Image Types. What is an Image. Acquisition of Images. Digital Images. Frequency Domain vs. Spatial Domain. Fourier Transform of a Signal and its Frequency Content. Frequency Content of an Image Noise, Edges. Spatial Domain Operations: Convolution Mask. Sampling and Quantization. Sampling Theorem. Image-Processing Techniques. Histogram of Images. Thresholding. Connectivity. Noise Reduction. Edge Detection. Hough Transform. Segmentation. Segmentation by Region Growing and Region Splitting. Binary Morphology Operations. Gray Morphology Operations. Image Analysis. Object Recognition by Features. Depth Measurement with Vision Systems. Specialized Lighting. Image Data Compression. Real-Time Image Processing. Heuristics. Applications of Vision Systems. Design project. 9. Fuzzy Logic Control. Fuzzy Control: What is Needed. Crisp Values vs. Fuzzy Values. Fuzzy Sets: Degrees of Membership and Truth. Fuzzification. Fuzzy Inference Rule Base. Defuzzification. Simulation of Fuzzy Logic Controller. Applications of Fuzzy Logic in Robotics. Design Project. Appendix. Matrix Algebra and Notation: A Review. Calculation of an Angle From its Sine, Cosine, or Tangent. Problems. Index.

Constraint network analysis of 3-dimensional insertion tasks

Flexible assembly machines may be improved and costs reduced by relaxing constraints on part fixturing accuracy and employing compliant devices in assembly effectors. An effector-mounted remote center compliance device that corrects for spatial misalignments of prismatic parts of general cross section has recently been demonstrated. This “spatial RCC” was designed by planning for the possible fine motion assembly contact states given a range of initial position and orientation uncertainty between the mating parts. These fine motion contact states are arranged in a constraint network in the fashion of a Petri net controller, however, the control transitions are mediated by compliances reacting to contact forces rather than from force sensing and discrete event controller schemes. A path through the constraint network of a square peg and hole task is found from initial to final assembly states. This path defines a single compliance relationship that is realized with a practical assembly device. Extensions of this design technique to other assembly tasks are discussed.

A Multiple RCC Device for Polygonal Peg Insertion.

This paper proposes a new passive compliant center device, the Multiple Remote Center Compliance (MRCC), for assembly tasks. The MRCC introduces a new azimuthal compliance over traditional passive compliance mechanisms that can effectively compensate the peg's orientation deviation for polygonal insertions. Besides, a special feature of the adjustable compliance provides capability to overcome the gravity effect. Non-vertical insertions therefore become possible. A spring-supported object in space is also adopted for stability analysis of this compliant device. Actual experimental assembly processes demonstrate promising results on polygonal insertions in both traditional top-down and horizontal directions.