Encoders

Encoders, Home Position and Safety Solutions

Student: Student Number: Tutor:

Carlos Vela P05253524 Dr. J Pu

Module: Machine Vision, Robotics and Flexible Automation Module Code: ENGT5202 Date: 27/02/2006

Carlos Vela Student Number: P05253524

MSc Mechatronics Machine Vision, Robotics and Flexible Automation

27/2/2006 Home Position and Safety

Table of Contents
Table ofContents............................................................................................................i List of Figures ................................................................................................................ii 1.0-Introduction .............................................................................................................1 2.0-Encoders..................................................................................................................1 2.1-Absolute Encoders...........................................................................2 2.2-Incremental Encoders ......................................................................4 3.0-Home PositionRoutine............................................................................................5 4.0-Other Functions of the Limiting Switch ..................................................................7 5.0-Software, Electrical and Mechanical Safety Solutions............................................7 6.0-Conclusion ...............................................................................................................8

i

Carlos Vela Student Number:P05253524

MSc Mechatronics Machine Vision, Robotics and Flexible Automation

27/2/2006 Home Position and Safety

List of Figures

Figure 1 - Optical Encoder Diagram..............................................................................1 Figure 2 - Code Disc with Gray-Code ...........................................................................2 Figure 3 - Multi-Turn Absolute Encoder.......................................................................3 Figure 4 - Incremental Encoder Principle......................................................................4 Figure 5 - Incremental Encoder Channels .....................................................................4 Figure 6 - ConsideredSystem........................................................................................5 Figure 7 - Home Position Routine Flow Chart ..............................................................6

ii

Carlos Vela Student Number: P05253524

MSc Mechatronics Machine Vision, Robotics and Flexible Automation

27/2/2006 Home Position and Safety

1.0-Introduction
Mechatronic systems use devices to measure position and motion. The most widely used devices to do so areencoders. Encoders can be absolute or incremental. Absolute encoders give a unique data for each angle of position. Incremental encoders give information about displacement but not absolute position. If incremental encoders are used a home position routine is required when powering on the system to place it in a known position. The elements used in a system can have more than one function andthey can be used to aid in the home position routine and as safety systems. Safety systems are needed in every system and one can have more than one safety solution to meet different risk levels.

2.0-Encoders
A tachometer is a device that provides information about the position and the speed of a motor. A servo motor uses that device attached to its shaft to provide the feedback signal. As longas servo motor are usually employed in systems with digital controllers the tachometer is digital as well. A digital tachometer is known as encoder. In servo motors the encoders usually employ optical technology.

A digital encoder consists of a disc containing transparent gaps that allow a beam of light to go through it. The beam of light is usually provided by a LED and is detected by...