How To Make Encoder Specification Simple

By Darren Pratt, encoder product specialist for SICK UK.

The introduction of the programmable encoder has greatly simplified the once lengthy and complex process of specifying encoders which control many precision processes in automation, robotics, printing, transport, textiles, packaging and general moving machinery control. The programmable encoder also has the potential to save significant cost.

Encoders are vital to the efficiency and control we often take for granted and precision monitoring of mechanical rotation is essential to many critical tasks and processes depending on speed, position and distance, safety and mechanical condition.  However, specifying standard encoders correctly for a particular machine and task can be slow, complex and risk error due to the daunting range of parameter choice.

Building user-programmability into encoder design and development offers the opportunity to save the time, expense and uncertainty in traditional encoder specification, as well as avoiding the need make compromises and short cuts.   Programmable encoders like those from SICK offer in-built simplicity and flexibility and can even be reprogrammed to reduce installation and life cycle costs.

 

Eliminating lengthy specification

Before the advent of the programmable encoder, the range of application requirements multiplied by the multitude of available encoder solutions offered literally millions of combinations which were each satisfied by a unique encoder model.

 

Typical preliminary questions were:

  • is absolute or incremental position information required?
  • what are the mechanical connections and interfaces with the plant?

 

Then choices included:

  • gearing
  • maximum total value
  • maximum frequency, signal level and resolution
  • connection to the control system
  • synchronization with a datum position

As well as the millions of potential encoder combinations to meet these, few of these questions have simple yes/no answers. Best solutions frequently lie on a long sliding scale, and each selection affects the implications of other decisions.

 

Easier replacement

As OEM-fitted encoders on existing equipment are typically long-lived, faults after decades of reliable service can be followed by prolonged downtime because a perfect replacement, or even a close fit, is not readily available. Back-up encoder stocks may have disappeared, along with all the essential machinery model information required to specify the correct encoder, meaning highly costly profit munching delays.

Complex specification over the phone may not match the realities on site, even with specialist engineering assistance, thanks to the possibilities for variation.

Instead, a major benefit of the programmable encoder is the flexibility that allows many key specification decisions to be made on site to match the machinery, rather than on preconceived assumptions.

 

Configure on Site

With a programmable encoder, such as the SICK DFS60 (incremental) and AFS/AFM60 (absolute), it can be configured on site to meet the specifications and control systems found. The features should include:

  • a selectable resolution to meet the mechanical gearing of the machinery
  • configurable signal levels across a wide supply voltage to meet the plant control system
  • electronic setting of the reference datum point or pulse

Synchronisation set-up can be performed at the push of a button with the electronic datum point, instead of lengthy manual alignment with the machine. By changing over to programmable encoders, the spares inventories and possible downtime are also minimised.  

Care must be taken to specify whether incremental or absolute encoders are required, and connection and mechanical compatibility with the machine must also be carefully assessed, as these factors cannot be reprogrammed.

 

Common operating platform

SICK’s common programmable platform has enabled separate incremental and absolute encoders to be created in all popular mechanical variations.  The free of charge programming software SOPAS, used to programme most of SICK’s configurable products, works with a cost effective PC programming dongle PGT-08-S to programme the encoder with the required settings for the application.

 

 

 

Conveyor tracking

Tracking the position of products transported on conveyor systems, allows marking to be applied directly to the correct place on the product despite continuous variations in the speed. Inkjet marking of filled bottles, or other packaging applications, are typical users, where the position data from the encoder is fed to the print head controller.

By using a programmable encoder, the engineer can install the encoder at the most convenient location for the line, and easily adjust the resolution to provide the required precision in data within the tolerances of the printer and different products.

 

Linear travel accuracy

Shaft revolutions are used to determining accurate linear travel in a wide range of horizontal or vertical winch operations, from crane handling to safe and noiseless scenery flat managing in theatres. The variations in the size of goods handled in different operations are easily accommodated by reprogramming the resolution of the encoder to achieve positioning accuracy every time.

In each of these applications, it can be seen that use of a programmable encoder saves the operator money by removing the need to use many different encoders to match changing application conditions, improves versatility and the speed of adaptation to different conditions, and ensures the highest possible accuracy of operation.