CAN Newsletter special issue
| Application | How to implement a CANopen drive - CANopen speeds food packaging - Drives move melting process in steel plant - CAN-based food concept runs food-slicing machine - Fleece-processing machines rely on servo drives |
|---|---|
| Device | CiA 402 drives - Electrohydraulic drives with CANopen - Servo controller - Positioning system - Servo motor - Pushing the limit of number of axes in CANopen - Survey of CiA 402 drives - CiA 402 in compact drives - CANopen frequency converters |
| Software | CAN and motion control in medical technology |
| Technology | CAN-based systembus reduces installation effort |
| Specification | Extensions to the CANopen device profile CiA 402 |
How to implement a CANopen drive according to CiA 402
This article describes how a CANopen drive can be developed successfully in a short time with the aid of software tools.
Modern drives systems can be adapted to custom-designed requirements and integrated into all sorts of communication networks. As a robust field bus system CANopen is increasingly used in drive applications. Users are facing the necessity of integrating the CANopen communication profile into their drives. The CANopen software must provide all components necessary for a CANopen drive. To achieve this, the following considerations play a decisive role:
- How is the fastest and most cost effective implementation in conformity with the CANopen standard achieved?
- How is the implementation carried out?
- Which software tools are available and which are useful?
CiA has published different standards for the communication in a CANopen network. The available CANopen services are defined in the communication profile CiA 301. Special drive functions with their parameters are defined in the “Device profiles Drives and Motion Control” CiA 402. The CiA 402 defines the behavior of a drive at the start, the configuration and the execution of motion sequences by a state machine.
Electrohydraulic drives with CANopen
Thanks to the linking of tried-and-tested mechanics with rapid actuator technology and high-resolution sensor technology, electrohydraulic axes with network interface have reached better accuracy and dynamics. Bosch Rexroth (www.rexroth.de) is continually separating drive physics and automation technology, at the same time opening up new areas of application for electrohydraulics. Here, the company favors open interfaces and supports all common network interfaces such as CANopen. The user can select the most appropriate and most economic solution from among the different drive technologies and combine them. By means of complete, ready-to-install electrohydraulic Plug & Run axes, the company assumes system responsibility, simplifying the incorporation of electrohydraulics in decentralized control systems.
Electrohydraulic axes have developed in terms of dynamics and precision: acceleration up to 80 g, rapid speed traverses of up to 10 m/s and control cycles in the milliseconds range have all become common industrial practice. In the case of punching presses, Rexroth axes can move forces of 30 tons with up to 1,500 double strokes per minute, in engrave mode even up to 4,000 double strokes can be achieved. With aluminum diecasting machines, electrohydraulic axes decelerate from 600 m/min to 0 m/min within 30 ms to 40 ms. Depending on the position measuring system, accuracies of up to 1 µm are common practice. But also incorporation in modern control architecture systems, with all the advantages of transparent data access, has been made considerably easier.
CAN-based concepts runs food slicing machine
Weber is a leading food slicing machine manufacturer from Breidenbach, Germany with subsidiaries in two other German locations and in Kansas City, MO, USA. Under the name Slicer, the company develops and produces a range of high-performance cutting machines for industry and trade. The systems process sausage, ham, meat and cheese. Weber slicing systems can be extended to form automatic processing lines: feeding, scanning, cutting, portioning, weighing, sorting, buffering, and automatic transport in packaging machines. Since the company’s founding in 1981 Weber has assembled machines and later developed their own machines for the food-processing industry. As a matter of fact, some of the Slicer machines sold in 1987 are so durable that they are still being used today.
The company’s slicing machines slice up to 2.5 tons of sausage or cheese per hour, which is the equivalent of 8,000 slices per minute. To illustrate this number: If you use four slices per sandwich for your children’s lunch, 8,000 slices is enough to pack their lunch box for two years.
Extensions to the CANopen device profile CiA 402
The CANopen device profile for drives and motion control (CiA 402) has been submitted to IEC for international standardization. It includes the type-specific PDO mapping for frequency converter, servo drive, and stepper motor. This type-specific PDO mapping simplifies the CANopen network configuration. The device profile also defines three additional synchronous modes of operation.
The profile defines a generic PDO mapping using seven TPDOs and eight RPDOs. Due to the fact that a generic CANopen device has only four pre-defined TDOs and four pre-defined RPDOs, the system designer has to assign CAN-IDs to the remaining PDOs and to switch them on. This is necessary even if the device manufacturer has pre-defined the corresponding PDO mapping parameter objects. In some drive implementations even these PDO mapping parameter objects have to be configured.
In order to reduce the configuration effort, the CANopen SIG Drives & Motion Control has defined the type-specific PDO mapping. In the device object (0x1000), bit 22 defines, which kind of PDO mapping is used (0 = generic mapping; 1 = type-specific mapping). All event-driven TPDOs are transmitted when entering the NMT operational state. The PDO set for frequency converter consists of three TPDOs and three RPDOs. The PDO sets for servo controller and stepper motor are identical. The first RPDO maps the control-word, while the second RPDO receives the target position, too. The third RPDO contains the target velocity instead of the target position. RPD= 4 is manufacturer-specific. The first TPDO sends the control-word. The second and third TPDO additionally map the current position respectively the current velocity. They are transmitted periodically every 100 ms. TPDO 4 is manufacturer-specific. The type-specific PDO mapping is in particularly recommended for drives and motion controllers with limited functionality.
CiA 402 in compact drives with computing power
The productivity of almost all types of machines depends to a great extent on the flexibility of the machine itself as well as on the required adjustment and setup time for the different products. Standstill times for adjustment are an important factor of the machine cost per produced unit of a product. That means, reduction of standstill time due to machine adjustment for a new product cycle will increase the efficiency and the output of fabrication. Several decades ago, as labor force used to be comparably inexpensive, manual-labor was not necessarily considered as important cost factor. But nowadays it is fairly uneconomic to require a lot of manual adjustments, when it comes to a product change on the same machine. It is even more uneconomic, if product cycles are very short or as high flexibility in manufacturing or a wide product range is required. A first step to increase efficiency and to shorten set-up times is of course to automate the procedure of manual machine adjustment. An additional motor and a suitable drive can be used surely for this purpose. This means that motor, gearbox, encoder, cables and drive replace the hand wheel. The usual consequence of this is that the main cabinet has to be enlarged to host the drives. A holding device with adaptation plate for the motor has to be mounted as a replacement of the hand wheel. In a cost sensitive area this will increase machine expense as well as assembling and wiring effort. To reach this market segment, Berger Lahr has developed an integrated compact drive that comes with a CiA 402 interface. Main cabinets do not require extra space for the drive, as the motor has its drive already integrated.
The integrated compact drive IclA N06x is based on an electronically commutated three-phase synchronous servo motor, which is permanently excited. IclA stands for “intelligent closed loop actuator”. The compact drive consists of an optional gearbox, servo motor, power and control electronics, position and velocity controller and a CANopen conform interface. With a 24-V DC power supply, a maximum phase current of 6 A and 71-W nominal output (N065) or up to 20 A with 100 W nominal output (N066) are possible. Different gear types as well as gear transmission ratios are available, which make the drive suitable for almost any kind of applications. A special focus was put on size minimization as size is one of the most important requirements in this field of application.
