16 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. zyxwv 43, NO. 1, FEBRUARY 1996 Practical Control Enhancement via Mechatronics Design James R. Hewit and Kaddour Bouazza-Masouf Abstract-Mechatronics is concerned with designing machines zyxwvu IT. EXAMPLE-KINEMATICS CONTROL with enhanced capabilities using advanced control methods. Here we describe how some of these advanced control methods have been evolved and how they can be applied effectively. The A technique ‘Or robotics is that Of resolved motion rate Control (RMRC). This iS a Control method zy -- resulting performance enhancement is explained by the use of a number of example case studies. It is shown that using these methods greatly improves the operational capabilities of mechatronics products and can, in ifications. The paper represents a survey of research work undertaken into Mechatronics control methods by the authors and their colleagues in recent years. for obtaining coordination between the various links compris- ing a robotic arm so as to enable the end-effector to be moved in torch at a constant speed along a straight line. This apparently simple operation requires the individual joints to be moved at rates which are not only different to each other but which vary with time. RMRC is, however, not restricted to robotics but can be applied with benefit to a wide variety of Mechatronics systems. Here we describe the benefits to be obtained in applying illustrates the quantum leap in performance obtainable using Mechatronics principles ,ll. Fig. l(a) shows the JCB zyxwv 520 materials handler. It is used way convenient to the task. many cases, lead to considerable increases in performance spec- in arc it is Often necessary to move the I. INTRODUCTION-MECHATRONICS CONTROL ECHATRoNICS has been described as “the design RMRC to a materials handling machine-an application which and manufacture Of products and systems possessing both a mechanical functionality and an embedded algorithmic control”. “mechanical functionality” that a Mechatronic system is de- It is intended? in this definition, to convey by the phrase in rough terrain work for stacking and unstacking palletised loads such as building bricks. signed to do physical, to have moving Parts, that The It is not design of the machine is centered around a telescopic boom at the end of which are situated the forks. The a data processing By “algorithmic control” it is meant that the controller which mediates the performance of the functionality is not simply a series of simple switching operations but that it entails the computation of some complex, probably multivariable, sequence of arith- metic logical and conditional functions. Thus is Mechatronics separated from the more traditional field of electro-mechanical design. It is the ability to use, at relatively low cost, the algorithmic designer to achieve a level of performance which not only up a new dimension to the product’s operation. in general it is not the technology which limits the perfor- mance. in the past, constraints were imposed by the speed of times, or by the cost of the computer which could lead to un- boom may be rotated around a horizontal axis through the base pivot. The configuration of the boom is therefore zyx “(T, e),’’ that is the forks may be moved radially, and circumferentially, “e.” However, because the major task for which the machine is used is with palletised loads, the natural coordinate system for the task is “(z,~).” Horizontal, zyxw “5,” movement is required to engage and disengage the forks while vertical “9” movement is required to raise and lower the pallets. In operate the “r” and “8” controls to obtain the “5” or “y” well placed to observe the forks’ movements and the difficulty is compounded by the fact that the “gain,, of the closed loop system of which he is a part changes and may even change power Of the microprocessor that the the noaechatronic version, the operator must simultaneously exceeds that Of previous designs but which Often ‘pens movement required. This is difficult because the operator is not the computer which lead to long sign. To see this consider the C<T)) movement needed to raise the forks vertically zyxwv an initial position on the ground to a final acceptably expensive products. Now however the technology of fast serial microprocessors, ASICS, and parallel processing means that in all but the most bizarre systems, the computing power is available at the right speed and the right cost. position high above the cab. For the first part of the movement the “T” movement is inward, becomes zero at the position where the boom is horizontal and is thereafter outward. To apply RMRC it is necessary to obtain the relationships between the task coordinates (2, y) and the lengths of the two rams zyxwvu (ET, Is). Clearly from Fig. l(b) this 1s (2.1) (2.2) (2.3) Manuscript received May 30, 1994; revised May 3, 1995. J R Hewit 1s with the Department of Applied Physics & Electronic & K. Bouazza-Marouf is with the Department of Mechanical Engineenng, F’ublisher Item Identifier S 0278-0046(96)01388-3. Mechanical Engineering, University of Dundee, Dundee DDl 4HN, UK. Loughborough University of Technology, Loughborough, Leicestershire LE1 1 3TU, UK z = (b + ET) cos Q y = (b + zyx ET) sin Q le2 = a ’ + b2 - 2abcosQ. 0278-0046/96$05.00 zyxwvut 0 1996 IEEE