CAN Newsletter special issue lift
| Specification | CANopen specification for lift control systems - Experiences with CANopen Lift networks |
|---|---|
| Application | Hamburg church with a view - CANopen lifts visitors |
| Device | CANopen encoders for elevator engineering - Safe and simple: CANopen encoders for lift technology - Devices with CiA 417 - Lift operating panels with CANopen interface |
| Tool | Tool support for CANopen Lift profile |
| Business | Vertical transport saves energy |
CANopen specification for lift control systems
CAN in lift control application has been used for many years by major lift manufacturing companies. In 2002 several medium-size companies decided to move to a standard higher layer protocol based on CAN. They decided to use CANopen as a basis for this standard. The goal was to have some kind of plug and play lift control system for any standard lift application. The result of the standardization work is the CANopen application profile for lift control systems CiA DSP 417. By use of this standard it is possible to build in maximum a lift application with 254 floors and eight parallel lifts.
In October 2003 the first CANopen lift control system prototype examples were demonstrated at the Interlift exhibition in Germany. A prototype lift system was assembled at the CiA and members booth made from devices by several manufacturers. The lift controller, the door controller, panels, displays, and other equipment: all communicating and exchanging data were integrated via the CANopen network. For the lift system designer it will be a great advantage to buy off-the-shelf products following the CANopen lift application profile specification, plug them together, and the lift control system will work with only a minimum of configuration effort.
This is particularly interesting for all small and medium-sized lift control builders. They do not depend on a specific device or control system supplier. Multi-sourcing is an important issue in order to provide a maximum flexibility and functional options.
Experiences with CANopen Lift networks
Lift control applications increasingly use decentralized and distributed control systems. These control systems require communication networks that link the sub-controllers, the “intelligent” sensors and the actuators. The level of compatibility is an important issue, if you want to buy and use off-the-shelf products.
The IEC T(echnical) R(eport) 62390 defines compatibility levels for network interfaces. Particularly for low volume applications, it is necessary to use high compatibility levels for network interfaces to minimize integration effort and to save costs.
Contrary to that, however is the fact that standardization keeps technology at a standstill. In order to be flexible and future-proved, it should be possible to extend and enhance the interface definitions. Flexibility is one of the key features of a network technology used in lift control applications.
Network technology
Controller Area Network (CAN), is a well-proven network technology. The physical layer (ISO 11898-2), as well as the data link layer (ISO 11898-1) are used in Millions of passenger cars and other control systems including embedded machine control, medical electronics, rail vehicles, and many more. CAN transceiver and CAN controller chips are available from more than 50 companies worldwide. The CAN controller chips are usually integrated in micro-controllers, which simplifies hardware design. The CAN data link layer protocol is robust and provides several built-in error detection mechanisms. The CANopen application layer protocol (EN 50325-4) was originally developed for embedded machine control applications. In 2004, about 1 Million CANopen devices were sold, which were used in applications such as off-highway vehicles, electronically controlled building doors, and embedded control systems.
The CANopen application layer provides communication services for real-time data transmission, for up- and downloading of configuration parameter and diagnostic information as well as for emergency messages. These standardized communication services use standardized protocols, e.g. PDO (process data object) protocol, SDO (service data object) protocols, EMCY (emergency) protocol.
The CANopen communication profile (EN 50325-4) defines the CANopen object dictionary. This dictionary is addressable by means of a 16-bit index and an 8-bit sub-index. This 24-bit addressing scheme overcomes the 11-bit CAN identifier limitation (2,048 addressable objects). The dictionary is the “heart” of each CANopen device.
Hamburg church with a view - CANopen lifts visitors
At the southern end of Hamburg stand the remains of the St. Nikolai church. The gothic style church was built in the 19th century and was an architectural masterpiece of its time. It is one of the few remaining landmarks from prewar Hamburg and after heavy raids by Allied forces in 1943 it was virtually the only structure left standing in the city center. The church was left blackened with soot and partially destroyed; the ruins were left standing in order to serve as a memorial to the victims of persecution in the Third Reich. The third highest church tower in Germany spirals up to an impressive 147-m height. In 2001 the church was restored and a platform in 75-m height was repaired to enable visitors to enjoy the splendid view over the city and port of Hamburg.
The lift that transports visitors up to the platform at a speed of 2.5 m/s is networked completely via the CANopen Lift profile CiA DSP 417. Böhnke and Partner (www.boehnkepartner. de) supplied the bp306 control unit with two CANopen interfaces.
The network consists of two separate CANopen sub-networks. One of them leads into the lift cabin, where a CLK-01 evaluates the cabin’s I/Os. The CLK-01 I/O modules provide signal inputs and outputs and calls in the lift cabin and control the display to indicate the lift position. They provide the CiA DSP 417 virtual devices “input panel unit”, “output panel unit”, and “door unit”. This line also incorporates the CAN absolute encoder by IVO (www.baumerivo.com). It is used to position the cabin in the church tower. It transmits PDOs cyclically every 20 ms. All other PDOs in the networks are event-triggered, the bus load is approximately 5%. Further CLK-01 units are connected via repeaters by Ixxat (www.ixxat.de); these I/O modules control LED dot-matrix displays, which visualize the position information of the cabin. They receive the position information from the absolute encoder, which transmits its data to the network.
A gateway connects the two CANopen sub-networks together at the CDG-01 diagnostic gateway. Located on the gateway is a modem, which enables the connection to a remote service center. The service center can thus diagnose and parameterize all devices on the two CANopen busses via this modem with the help of the CANwizard software.
Safe and simple: CANopen encoders for lift technology
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 CiA DSP 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.).
