Passive Compliance Device Research Articles

Towards Robust and Effective Passive Compliance Design of End-Effectors for Robotic Train Fluid Servicing

Without mechanical compliance robots rely on controlled environments and precision equipment to avoid clashes and large contact forces when interacting with an external workpiece, e.g., a peg-in-hole (PiH) task. In such cases, passive compliance devices are used to reduce the insertion force (and in turn the robot payload) while guiding corrective motions. Previous studies in this field are limited to small misalignments and basic PiH geometries inapplicable to prevalent robotic and autonomous systems (RASs). In addition to these issues, our work argues that there is a lack of a unified approach to the development of passive compliance systems. To this end, we propose a higher-level design approach using robust engineering design (RED) methods. In a case study, we demonstrated this general approach with a Taguchi design framework, developing a remote centre compliant (RCC) end-effector for robotic train fluid servicing. For this specific problem, a pseudo-rigid-body model (PRBM) is suggested in order to save enormous computation time in design, modelling, and optimisation. Our results show that the compliant end-effector is capable of significantly reducing the insertion force for large misalignments up to 15 mm and 6 degrees.

A Stiffness Variable Passive Compliance Device with Reconfigurable Elastic Inner Skeleton and Origami Shell

Devices with variable stiffness are drawing more and more attention with the growing interests of human-robot interaction, wearable robotics, rehabilitation robotics, etc. In this paper, the authors report on the design, analysis and experiments of a stiffness variable passive compliant device whose structure is a combination of a reconfigurable elastic inner skeleton and an origami shell. The main concept of the reconfigurable skeleton is to have two elastic trapezoid four-bar linkages arranged in orthogonal. The stiffness variation generates from the passive deflection of the elastic limbs and is realized by actively switching the arrangement of the leaf springs and the passive joints in a fast, simple and straightforward manner. The kinetostatics and the compliance of the device are analyzed based on an efficient approach to the large deflection problem of the elastic links. A prototype is fabricated to conduct experiments for the assessment of the proposed concept. The results show that the prototype possesses relatively low stiffness under the compliant status and high stiffness under the stiff status with a status switching speed around 80 ms.

The vibratory alignment of the parts in robotic assembly

PurposeThis paper aims to consider the experimental and theoretical investigation of the vibratory alignment of the peg-hole, when the peg is fixed in the remote centre compliance (RCC) device, and the vibrations are provided either to the hole or to the peg.Design/methodology/approachThe experimental analysis of the circular and rectangular peg-hole vibratory alignment using the attached to the robot arm RCC device, under vibratory excitation of the hole, has been performed. The parameters of the vibratory excitation and the part-to-part pressing force influence on the alignment process have been analysed. The mathematical approach of the vibratory alignment using the passive compliance device with the vibrations provided to the peg has been proposed, and the simulation has been carried out.FindingsThe research has approved the applicability of the RCC device for both of the vibratory alignments of the non-chamfered peg-hole parts either circular or rectangular ones. The compensation of the axial misalignments has been resulted by the directional displacement of the peg supported compliantly. To perform the successful alignment of the parts, it has been necessary to adjust the frequency and the amplitude of the vibrations, the pressing force, the lateral, as well as the angular stiffness of the device.Research limitations/implicationsThe experiments on the vibratory alignment of the rectangular peg-hole parts have been carried out considering only the translational misalignment moved into one direction. The non-impact regime of the vibratory alignment has been analysed.Practical implicationsThe obtained results can be applied in designing the reliable and efficient devices of the vibratory assembly for the alignment of the non-chamfered peg-hole parts, as well as for chamfered ones, if the axial misalignment exceeds the width of the chamfer. The vibratory technique and passive compliance provide possibility to accomplish the assembly operations using the non-expensive low accuracy robots.Originality/valueThe new method and the mathematical approach of the vibratory assembly using the RCC device can ensure the reliable alignment of the non-chamfered parts, chamfered circular and the rectangular ones, in case the axial misalignment exceeds the assembly clearance, and prevent jamming and wedging.

조립 로봇용 가변 수동 강성 장치의 설계

조립 로봇용 가변 수동 강성 장치의 설계

Experimental research of vibratory alignment using passive compliance devices

The experimental analysis of interdependent vi-bratory alignment of the shaft and bushing type parts of rectangular and circular cross-section is carried out, using the passive compliance devices of different construction. An experimental setup for vibratory assembly was mounted, when the shaft is fixed in the passive compliance device and pressed by predetermined force towards the bushing, which is based on the vibratory platform and subjected to vibratory excitation along the axial direction. The alignment duration dependencies on axial misalignment, frequency and amplitude of vibrations and initial pressing force of the device were made. DOI: http://dx.doi.org/10.5755/j01.mech.20.2.6945

Screw System Approach to Physical Realization of Stiffness Matrix With Arbitrary Rank

It is possible to realize the desired compliance characteristics of a robot in a form of a passive compliance device, which demands the synthesis technique of a stiffness matrix by parallel connections of line and/or torsional springs. In this paper, the stiffness matrix is expressed in terms of the screw coordinates with respect to the basis consisting of its eigenvectors, thereby the synthesis equation is derived. Examination of the numbers of free design parameters involved in the synthesis suggests that a line or free vector for a spring can be freely selected from the induced wrench space depending on the rank of the stiffness matrix. The recursive synthesis method that allows one to select the positions or directions of the springs from the screw system spanned by the induced wrenches of the given stiffness matrix is proposed.

An Analytical Approach to the Design of Compliant Hand for Assembly Operations.

An analytical method to the design of compliant hand appropriate to given assembly operations is presented. Use of passive compliance devices in mating operations is effective in order to prevent excessive contact forces and to guide an assembled part to its goal location despite of positioning errors among the parts. Methods to design passive compliance devices are thus required. First, quasistatic equilibrium conditions are established based on the kinematic and the static analysis of mechanical contacts. Second, feasible candidates for the desired end-point compliance are calculated based on the equilibrium conditions. Next, the configurations and the spring constants of virtual springs consisting of the desired compliant hand are designed through decomposing stiffness matrices. Simulation of mating operations is then introduced in order to determine the magnitude of spring constants of virtual springs and to verify whether the derived compliant hand enables the mating operations successful or not. Finally, one numerical example is shown to illustrate the process of the design of compliant hands.

Hybrid compliance control for intelligent assembly in a robot work cell

This paper introduces a novel approach of using Hybrid Compliance Control (HCC) in robotic assembly. The approach uses active implicit compliance control in conjunction with a Passive Compliance Device (PCD) for assembly tasks. The active control provides force feedback to enable the robot to follow an assembly path during task execution, and the PCD supplements corrections for instantaneous time-dependent assembly path uncertainties that arise from inherent errors in the system and manufacturing irregularities. This HCC strategy resulted in lesser force impact on the end effector during task executions, a higher number of successful assemblies, and did not significantly affect implementation costs. Experiments conducted to validate the HCC and the redundancy built in, displayed positive indicators, implying that the concept is transferable to automated assembly lines.

Insertion Force Recognition by Modelling and Simulation of Assembly Systems with Accomodators

This paper concerns passive compliance devices, where compensation takes place as the direct effect of the contact forces generated between the parts during insertions in assembly tasks. These devices contain compliant elastic elements which can flex to correct initial errors. The present work focuses on evaluating insertion force in relation to the different passive compliance device design parameters. Theoretical model of insertion task is implemented in a simulation program capable of specifying the parameters indicating insertion progress and the insertion field.

Robotic Instrumented Complaint Wrist

A robotic complaint wrist which combines a passive compliance device and a displacement sensor has been developed and tested. The device provides the necessary flexibility to accommodate transitions between the position control and force control modes, and avoid large impact forces as a robot makes contact with parts, as well as correct positioning errors and allow the relaxation of tolerances in assembly and manufacturing operations. The device installed between a robot arm and end-effector is composed of two parts: a passive compliance device and a sensing mechanism. The passive compliance is provided by a rubber structure; its configuration can be arranged to yield the desired stiffness ratio along and about each axis. The sensing mechanism consists of a six-joint serial linkage with a transducer at each point. The measured deflection is used to actively control the contact forces and compensate for the positioning error during motion and contact. In this paper, the design features of two prototypes of the device are described. A systematic hybrid position/force control scheme incorporating the device is presented.

Isoelastic behavior of parallel robots

SUMMARYThis paper presents a particular architecture of a parallel robot which is characterized by a diagonal stiffness matrix. This result suggests the use of a parallel robot in the final phase of insertion as a passive compliance device. The stiffness rate of this device is controlled by the gain of the feedback loop. As the correction of small angular misalignments due to contact forces do not generate lateral errors and vice versa, we have the equivalent of an isoelastic swivel.