Mechatronic Redesign of Slider Crank Mechanism

Mechatronic design efforts have been and continue to be heavily investigated in the development of robotic manipulator arms. However, little effort has been devoted to mechatronic redesign of traditional two-dimensional mechanisms which mechanical engineers get exposure to when they study subjects such as kinematics and mechanism design. In this paper a feasibility study for controlling the motion of the popular slider crank mechanism with appropriate sensing and actuation is elaborated. The results indicate that a variety of motion profiles can be derived from the same mechanism without involving any mechanical redesign. Many of the control approaches that have been heavily investigated in the field of robotics are readily applicable to such mechanisms. The synergistic combination of mechanical design, soft computing, sensing, instrumentation, and control is likely to bring about unprecedented versatility and performance levels in the hardware realization of machines based on these mechanisms. INTRODUCTION There has been a growing number of applications and product development at the interfaces of traditional disciplinary boundaries of mechanical, electronics and computer engineering fields within the broad area of engineering education in recent years. This has necessitated the development of a new and interdisciplinary field of pedagogy "Mechatronics". "Mechatronics” synergistically combines engineering mechanics, electronics, sensors, actuators, soft computing and control [1,2]. Traditionally, mechanisms, linkages and cams are designed with the assumption that "input motion" will be provided by a constant velocity motor [3,4]. The design involves developing a mechanical arrangement that will provide the desired "output motion" utilizing a motor running at a set number of revolutions per minute (rpm). Any change of desired "output motion" therefore required the development of a new mechanical device with this approach. Mechatronic redesign not only allows these mechanisms to enhance performance but to exhibit some degree of flexibility to adapt to varying of task requirements. The slider crank mechanism is used in a variety of machines when there is a need to convert rotary motion into reciprocating motion and vice versa. As with most other mechanisms the input motion to a slider crank mechanism is typically from a motor or other rotating device running at constant rpm. The resulting motion is therefore a reciprocating motion of the slider with every cycle of the crank. Also the forward and return motion of the slider has the same duration. An educational project involving the study of dynamic model and motion characteristics of such a device has been reported in reference [5]. For all requirements involving slow forward motion (such as, may be necessary for cutting action, photocopying etc.) and a faster return motion (no action, just to reset quickly to save time before the next action stroke), traditional approach has been a complete mechanical redesign resulting in what are popularly called “Quick Return Mechanisms”. Offset slider-crank, Drag link, Whitworth, Crank Shaper etc.[3] are some examples of such mechanisms. Traditionally no–effort has been made to integrate appropriate sensors, to determine the crank angle, and appropriate controllable actuator that can apply variable torque to the crank, with such mechanisms. Such “Mechatronic redesign” with appropriate sensing and control action enables the traditional slider crank mechanism to perform a variety of motion patterns. 1 Copyright © 2002 by ASME dt d φ dt d φ d φ dx dt dx J = ] ]/[ [ = ) /2l)sin(2φ (r + rsinφ = = J 2 dφ dx )] /2l)sin(2 φ (r + ) )/[rsin( ( = J = 2 dt dx dt dx 1 dt dφ φ )] /2l)sin(2φ (r + ) [rsin( φ)}] (r/l)cos(2 + ) ( {rcos ) ( [ = ] [ J = 2 2 dt dφ dt x d dt dφ dt dJ dt x d 1 dt φ d 2 2