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DC Motor Controller Offers Great Flexibility
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Date Added: 15th June 2011
Maxon Motors' have a fine reputation for providing an impressive range of DC electric motors and EPOS motor controllers that are operated through a variety of industry standard field buses to give precise control in just a few milliseconds. So what is CANopen?
Simply stated, CANopen is a communication protocol and device profile specification. It is mostly seen in embedded systems for compact automation and motion control applications.
The basic CANopen profile is defined in CiA 301 standard and in the EPOS Controller range, the automation profile to CiA 401 and motion control profile CiA 402 are all used to reduce external interfaces and inter-device cabling; thus reducing development times and costs for new products.
CAN controllers are very cost effective in that they can be found embedded in a high proportion of compact microcontrollers and processor devices. With CANopen applications, device developers have the flexibility to exchange components without having to go back to first principles as the interface protocols are standardised.
For example, if a stepper motor, supplied with its relevant controller, has a replacement controller from another manufacturer, there is little to change in the controller's CANopen profiles and both drive systems appear almost identical on the CANbus.
Complex control is easily achieved even for smaller devices including the synchronisation of individual drives. CANopen can operate in three modes to synchronise motors, each with their strengths and drawbacks.
Interpolated Position Mode (known also as PVT - position & velocity versus time) is where the machine controller calculates all drive movements individually and then generates existing support points using position and velocity at discrete intervals. These are written into the positioning controller's message buffer. From this, the message controller calculates reference values for positioning control through linear or 3-D interpolation.
The local timers within the positioning controller are then synchronised on the CAbus with SYNC messages.
The benefit for PVT mode is that the periods between the support points are between 10ms and 100ms and the real-time requirements are low. The drawback is that additional synchronisation with external sensors is too slow for rapid motion control.
Velocity Modes are used where greater dynamics in motion planning can be achieved if the motion planning and some drive control are carried out in the CANopen master. The controllers are then operated in "profile velocity" mode. The Maxon EPOS2 positioning controllers allow a "true velocity" mode whereby velocity reference values are fed directly into the controller, this allowing a high level of control dynamics.
The drawback is the bus load and there are greater demands on the master's real time capacity with control architecture cycle times of between 2 and 5 ms.
Profile Torque Mode & Current Mode - In this arrangement, both the positioning and velocity controller is located in the CAN Master device and torque or current set values are specified via CAN-bus. To enable this to happen, CANopen specifies "profile torque mode for motion control products. Maxon offers an alternative "current" mode for its EPOS2 controllers, which is an essential requirement to create a large dynamic range for its coreless motors.
The benefits are that they maximise dynamic range and complex algorithms can be be implemented in the master (which is ideal for robots). The drawbacks are that real-time capacity requirements are high, high demands upon the CANbus and short cycle times.
Maxon Motor offers a whole family of CAN enabled universal positioning controllers which are ideal for use in conjunction with DC and EC motors up to 700 W out put. The EPOS range of miniaturised controllers are also compatible with USB, RS232 interfaces fro maximum flexibility. For more information, please contact Maxon Motors regional team for more information.
More from this supplier | More from this category: Motors, controls and Drives
More from this subcategory: Motor Controllers