The Data Courier
Omron RFID application stories

Episode 6: Motion control for high-speed conveyor

Motion control for high-speed conveyors, such as OHT’s and sorters, are often performed with mechanical flags that use photoelectric sensors and optical communications devices. Unfortunately systems based on mechanical flags can suffer from position displacement caused by shocks and vibration that can then result in malfunctions. Wear-and-tear can also lead to problems related to light-source deterioration and interference due to dirt can also occur.

In order to develop a faster system, a greater level of autonomy is needed and RFID technology would give the required level of autonomy but even then the communications speed would probably be too slow. The solution is to mount ID tags to the OHT’s and install antennas at stations and junctions as required to give speedy responses. The clever system then stores the OHT unit numbers and other relevant information in the ID tags. When an OHT reaches a station reads the unit number with the antenna and sends the OHT to the specified location by switching points as necessary via the control system (e.g., PLC) connected to the antenna.

The excellent results provided using an RFID system is that they do not have mechanical parts such as mechanical flags. This makes malfunctions much less likely to occur and as they are unaffected by an environment where there is dirt, dust etc. they eliminate the need for maintenance. The reading time when the unit numbers are set with 8 alphanumeric digits is approximately 5 ms thus enabling operation with a travel speed of 350 m/min (1,180 ft/min). This will clearly help with performance improvements in conveyance devices in the future, for example much faster OHT’s.

The salient features of equipment applied to this system is the ability to high-speed read and write (212 Kbps) enabling the transmission of 8 bytes of information in 5 ms and 128 bytes of information in just 14 ms. Furthermore the Fe-RAM is used for the memory and so the reading and writing times are the same; the maximum number of accesses is 1 billion times. To achieve stable communications in most factory automation environments, which need high noise, resistance the communications frequency used is in the 13-MHz band.
For simplicity of installation in different locations the ID controller is equipped with a self-execution mode that allows all types of control without a host system programme.
Note: It is worth considering when mounting unit that the communications distance is reduced if there is metal immediately behind the ID tag.

Micromech is the systems integrator for Omron RFID systems, if you wish to find out more contact Stirling Morley on 01376 333311 or stirling@micromech.co.uk

‘Micromech, keeping track with Omron’