Page 147 - Mechatronics with Experiments

CHAPTER 3

MECHANISMS FOR MOTION

TRANSMISSION

3.1 INTRODUCTION

Every computer controlled mechanical system that involves motion is built around a basic
frame of a mechanism which is used to transmit the motion generated by the actuators to
the tool. The actuators provide purely rotary or purely linear motion. For instance, a rotary
electric motor can be viewed as a rotary motion source while a hydraulic or pneumatic
cylinder can be viewed as a linear motion source. In general, it is not practical to place the
actuator exactly at the location where the motion of a tool is needed. Therefore, a motion
transmision mechanism is needed between the actuator and the tool. Motion transmission
mechanisms perform two different roles,
1. they transmit motion from actuator to tool when the actuator cannot be designed into
the same location as the tool with the desired motion type,
2. they increase or reduce torque and speed between input and output shafts while
maintaining the power conservation between input and output (output power is input
power minus the power losses).

The most common motion transmission mechanisms fit into one of three major categories:
1. rotary to rotary motion transmission mechanisms (gears, belts, and pulleys),
2. rotary to translational motion transmission mechanisms (lead-screw, rack-pinion,
belt-pulley),
3. cyclic motion transmission mechanisms (linkages and cams).

Common to all of these mechanisms is that an input shaft displacement is related to the
output shaft displacement with a fixed mechanical relationship. During the conversion,
there is inevitable loss of power due to friction. However, for analysis purposes here, we
will assume ideal motion transmission mechanisms with 100% efficiency.
The efficiency of a motion transmission mechanism is defined as the ratio between
the output power and input power,
P out
= (3.1)
P
in

Mechatronics with Experiments, Second Edition. Sabri Cetinkunt.
© 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd.
Companion Website: www.wiley.com/go/cetinkunt/mechatronics

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