Derek G. Chetwynd

Conceptual Design and Dimensional Synthesis of a Novel 2-DOF Translational Parallel Robot for Pick-and-Place Operations

This paper deals with the conceptual design and optimal dimensional synthesis of a novel 2-DOF translational parallel robot for pick-and-place operations. In a conceptual design phase, the conditions for generating such kinds of parallel robots are investigated, leading to the invention of a 2-D version of the Delta robot. Combining this robot with a 1-DOF feed mechanism, a hybrid robot can be created which is particularly suitable for transporting objects at very high speed in a plane plus a relatively slow or step-by-step, yet long distance motion, normal to the plane. The kinematic optimality of the 2-DOF translational parallel robot is achieved by minimizing a global and comprehensive conditioning index subject to a set of appropriate constraints. The application of this robot to the development of a device for quality inspection of rechargeable batteries is used to demonstrate its applicability.

Metrology and properties of engineering surfaces

1. Surface measurement and characterization.- 2. Fractal geometry in engineering metrology.- 3. Topography instrumentation.- 4. Surface topography filtering.- 5. Areal autocorrelation and spectral analysis of surface topography.- 6. Calibrating scanning probe microscopes.- 7. Characterization of cylinder bores.- 8. Surface characterization using neural networks.- 9. Hardness measurement.- 10. Surface damage in brittle materials.- 11. Thin-film conducting polymer bearings.- References.

Dynamic Formulation and Performance Comparison of the 3-DOF Modules of Two Reconfigurable PKM—the Tricept and the TriVariant

Utilizing the virtual work principle, this paper presents a method for the inverse dynamic formulation of the 3-degree-of-freedom (DOF) modules of the well-known Tricept robot and a newly invented hybrid robot named TriVariant. The TriVariant is a modified version of the Tricept, achieved by integrating one of the three active limbs into the passive one. Both local and global conditioning indices are proposed for the dynamic performance evaluation and comparison of these two robots. These indices are designed on the basis of the maximum actuated joint force required for producing a unit acceleration of the mobile platform. For a given set of geometrical and inertial parameters, it has been shown that the TriVariant has a similar overall dynamic performance compared with that of the Tricept.

Recent advances in traceable nanoscale dimension and force metrology in the UK

It is now fully appreciated that metrology will play an integral role in the successful development and commercialization of micro- and nanotechnology. To this end, the UK Government, through the National Measurement System, funded several groundbreaking projects in its 2002–2005 Programme for Length. This paper will briefly describe the background of the research, concentrating on the technical details of the projects. The Programme for Length normally only funds work into dimensional metrology but this funding cycle also funded work into low force metrology as this area is crucial to most mechanical probing techniques. The projects described include a traceable areal contacting instrument designed to calibrate areal transfer artefacts and hence offer traceability for industrial areal instruments, the production of the areal transfer artefacts, the development of Internet-based softgauges for profile parameters, a primary low force balance with a force resolution of 50 pN and the development of methods for measuring complex micro-scale structures. Amongst others, the projects involved collaboration with PTB, TNO, Taylor Hobson, AWE, Rubert & Co. and the Universities of Warwick, Huddersfield and Eindhoven.

A Method for Estimating Servomotor Parameters of a Parallel Robot for Rapid Pick-and-Place Operations

By taking a 2-DOF high-speed translational parallel manipulator as an object of study, this paper presents an approach that enables the servomotor parameters of parallel robots for pick-and-place operations to be estimated in an effective manner using the singular value decomposition. These parameters include the moment of inertia, speed, torque, and power of the motor required for producing the specified velocity and acceleration of the end effector. An example is given to determine these parameters of a device for the rechargeable battery quality inspection.

Kinematic design of a 5-DOF hybrid robot with large workspace/limb-stroke ratio

This paper deals with the conceptual and kinematic designs of a 5-degree of freedom (DOF) reconfigurable hybrid robot. The robot is composed of a 2-DOF parallel spherical mechanism that is serially connected with a 3-DOF open loop kinematic chain via a prismatic joint. Somewhat similar to the well-known Tricept robot, this design has the merit that a relatively large workspace/limb-stroke ratio can be achieved thanks to the decomposition of the motions of the output link into the 2-DOF rotation and 1-DOF translation. As with the Tricept, the robot is well suited for use as a plug-and-play module to configure different machines. The dimensional synthesis of the 2-DOF spherical parallel mechanism is carried out by the monotonical analysis of the design variables versus a global conditioning index represented by the mean of the minimum singular value of the Jacobian, leading to the solution of two nonlinear equations due to the limb length constraint and nearly axial symmetry requirement of the kinematic performance. The results of the dimensional synthesis are given via examples.

A controlled-force stylus displacement probe

A novel design of displacement profiler with a controllable stylus force is presented. It provides highly controlled conditions for contact measurement of, for example, small step heights or surface roughness. Incorporating an electromagnetic force actuator and force feedback control, the profiler provides electronically selectable contact force in the range of 0.01–10 mN and gives a constant static and dynamic loading. In a typical configuration, it has a range of a few micrometers with a discrimination to better than 1 nm at a bandwidth higher than that of a conventional stylus instrument.

Roundness measurement using limacons

Abstract Most roundness measuring systems which find automatically the ‘reference circles’ to a profile have used, for convenience, a limacon figure as an approximation to a circle. However this figure has important geometrical properties relevant to normal roundness measurement and can be regarded as the bais of an analytical system rather than an instrumental convenience. This paper examines some of the implications of the limacon method under practical conditions by comparison with circular references. It includes a comparison of roundness measurements taken using limacon references according to minimum zone, minimum circumscribing, maximum inscribing and least squares criteria

Sub-nanometre displacements calibration using X-ray interferometry

The technology of X-ray interferometry has been applied to the calibration of micro displacement transducers at sub-nanometre levels. Using the lattice spacing of high perfection silicon of semiconductor industry grade as a reference, the system provides a portable, absolute length standard with an accuracy of 1 part in 106 traceable to primary standards, a demonstrated resolution of 10 picometres and a double-beam phase-quadrature output for providing sensitivity to the direction of motion of the moving interferometer blade. The system and its performance are discussed in detail, methodologies for the analysis of data are presented and an application to the calibration of Talystep transducers (both absolute and comparative between models) for overall accuracy and thermal drift is reported. The design and performance of a portable instrument using a miniature X-ray source is also reported.

A Method to Formulate a Dimensionally Homogeneous Jacobian of Parallel Manipulators

This paper presents a general and systematic approach to formulate the dimensionally homogeneous Jacobian, which is an important issue for the dexterity evaluation and dimensional synthesis of f-degrees-of-freedom (DOF) (f ≤ 6) parallel manipulators having mixed rotational and translational movement capabilities. By the utilization of f independent coordinates to describe the specified motion types of the platform, the f × f dimensionally homogeneous Jacobian is derived directly from the generalized Jacobian, provided that the manipulator has only one type of actuator. The condition number of the new Jacobian is then employed to evaluate the dexterity of two typical 3-DOF parallel manipulators as an illustration of the effectiveness of this approach.