04.03.2016

AGH UST researcher develops cheaper optical encoder


Encoders “translate” information regarding the position of a construction into an electrical signal. They can be used, for example, in lifts, robotic manipulators or optical computer mice. Thanks to encoders, machines can be given precise tasks to perform. An optical encoder cheaper than its competitive solutions has been developed by Tomasz Dziwiński of the Faculty of Electrical Engineering, Automatics, Computer Science and Biomedical Engineering.    

 

The researcher has applied pioneering solutions with regard to coding information. 

 

A fundamental factor standing in the way of the technological revolution of the 20th century was the idea of feedback. The feedback loop makes it possible to achieve a determined value in a system of automatic control. 

 

“Information about the current position of a cabin in a shaft makes it possible for the lift to stop at chosen floors. Thanks to feedback, the end of a robotic manipulator reaches the predetermined coordinates with a very high precision,” explains the developer to the Polish Press Agency. “In each case we deal with a regulation system which holds information regarding a certain physical value, such as speed or position. However, before the information is passed on to an electronic control system, it is necessary to convert the physical value into a certain electrical signal.”  

 

One of the basic types of position transducers into an electrical signal is the encoder. For the purpose of measuring the angular position in rotary motion we use rotary encoders, and for the purpose of measuring the position in translational motion we use linear encoders.   

 

As Dziwiński explains, in technique and technology there are two basic types of encoders: absolute and incremental. The former type always measures the value in relation to position zero. On the other hand, incremental encoders generate a series of signals in time, when the position of an encoder changes.

 

Absolute encoders are more technologically advanced and require more precision in the production process, but in many applications they are indispensable and cannot be replaced by cheaper and simpler incremental encoders. Tomasz Dziwiński’s invention is an optical absolute encoder, durable and precise. It has a rotary code disk and a sensing element. The encoder’s disk rotates together with the shaft on which it is positioned, and the motionless sensor can determine the position of the disk, reading information coded in it. 

 

“A simple optical sensor can take pictures of low resolution, but with a large frequency. These types of sensors are built into optical computer mice, where the picture of the surface under the mouse is analysed and compared with a picture taken a moment before. However, in order to enable the use of such sensors in encoders it was necessary to develop a suitable way of coding information on the encoder’s disk,” says Tomasz Dziwiński.   

 

He explains that in classical encoders a data word is a string of logical states represented by numerals 0 and 1. Such a string can easily be converted from the binary system into decimal, and then assigned a suitable angular value expressed in degrees.   

 

The encoder presented by the AGH UST engineer works in a completely different way. In this case, it is not the string of logical states, but it is the matrices of states that are the object of interpretation. Coding information in the form of logical matrices is very advantageous, as it saves space on the code disk. “In order to code 4096 positions on the disk in a classical solution we need coded data words composed of 12 bits – the disk must contain 12 data lines. In the developed solution, in order to code positions we only need a 4x4 matrix – the disk must contain only 4 data lines,” explains the researcher.   

 

The price of optical absolute encoders is very often more than 1,000 PLN, because they contain specialist optical sensors and require densely coded information on a precise code disk. As Dziwiński estimates, his solution can lower the production costs of optical absolute encoders and contribute to the miniaturisation of encoders.   

 

In the first place, his solution is aimed at industrial clients. Customers of this type often choose components and parts of well-known and well-established producers, companies of many-year experience in the field. The production of encoders according to the suggested project would not involve any additional costs related to the development of mechanical parts (housing, shaft, shaft bearings, disk), as these would remain identical with the ones used so far. 

 

Source: Polish Press Agency – Science & Scholarship in Poland