Safe and simple - CANopen encoders for lift technology

Sicher und einfach - CANopen-Encoder für Aufzüge By Klaus Matzker, Fraba Posital, (E-Mail:info@posital.de)

Switches and cam rails are fragile components. Mechanically fastening and adjusting them is time-consuming, moreover, adapting them to specific applications often requires many parallel switches and therefore many control inputs. However, there is a simpler and less troublesome solution: In lift technology, for instance, a position measuring system based on absolute rotary encoders can be used. This minimizes the number of mechanical components: limit switches and input channels for the control system are rendered unnecessary. Furthermore, the lift can easily be adjusted to on-site conditions. Fraba Posital’s (www.posital.de) CANopen encoders conform to the new CANopen application profile for lifts CANopen CiA-417.

Fieldbus system, CANopen, EDS files – those terms evoke thoughts of training courses, specialized staff and programming devices. After all, starting up and diagnosing a device consumes more and more time and money as its parameterization and communication become increasingly complicated. As a remedy, device profiles for the different field bus systems were defined in industrial automation, e.g. for absolute rotary encoders. While this has helped to reduce programming and configuration efforts, a lot of work still remains to be done on the installation site. Therefore, application profiles now also exist for CANopen in elevator technology. Led by the CAN in Automation (CiA) international users’ and manufacturers’ group, major lift producers have joined forces to define standardized profiles (lift control, door control, positioning, operator panel etc.).

The application profiles operate with virtual devices, which may sound more complicated than it ultimately is for the user. Individual “lift functions” which constitute a function module are assigned to each virtual device. One virtual device, for instance, is the Car Position Unit, which determines the cabin’s position and, if necessary, its speed and other data. Several virtual devices can be mapped to one physical device. In the example given here, several car position units can be mapped to a single absolute rotary encoder due to its high-performance 16-bit micro-controller. The key benefit here is that one virtual device transmits the position value directly converted into millimeters to the control system, while another one simultaneously transmits raw position data at a maximal resolution to the frequency drive. By defining all virtual devices and their functions in the lift’s application profile, configuration efforts are minimized, which enables assembly and maintenance staff to concentrate on their essential tasks. The absolute rotary encoder merely has to be mechanically installed and wired. The device addresses are set via rotary switches – that is all it takes to integrate the device into an application. The low cost model’s address is set directly via CAN.

Robust and reliable

Fraba offers a wide range of customized CANopen encoder solutions with different housing models, different transmission media (fiber optic or copper) and a variety of connection technologies. The tried and tested detachable interface unit comes with a terminal strip for easy wiring. The device address is set via a rotary switch. Competitively priced models are available with cable exit or D-sub plugs. All encoders meet high EMI standards and resist mechanical stress caused by vibrations, axial forces and radial forces. For the first time, the company’s lift encoders provide CANopen encoders for industrial use featuring application profiles specific to lifts.

Summary

Absolute rotary encoders do away with end switches and input channels in the control system. Due to their rugged design and their power-failure safe measuring, they provide high safety and reliability. At the same time, position determination via encoder allows for easy extension of the control program, adding functions like smooth acceleration and deceleration of the passenger cabin. Integration into the CAN network is made easy by the new CANopen application profiles.

Source: CAN Newsletter Special Lift 2005 (www.can-cia.org/newsletter)