CAN Network Adjusted for Advanced Motion Control

DN Staff

March 8, 2011

4 Min Read
CAN Network Adjusted for Advanced Motion Control

Thegoal for Animatics Corp. of connectingits new Class 5 SmartMotors over a standard CAN network without the need for adedicated master, allowing them to communicate on an equal footing and shareall information and processing resources available on the network has beenachieved. An array of these integrated servos can now act as aparallel-processing system capable of multi-axis coordinated motion, high-speedcontouring, electronic camming and gearing.

How the company achieved this by adapting theindustry-standard CAN network is a key point in Animatics' system designphilosophy.

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Leveragingan Industry Standard

"CANis amazing technology that providesspeed up to a megabit and a hardware infrastructure to decode messages andaccelerate system performance, plus built-in arbitration and data collisionfeatures that create an excellent interface," says Robert Bigler, CEO ofAnimatics Corp.

Biglersays that to use CAN as an industrial network, the choices for a systemdesigner are to use either CANopen and DeviceNet, both of which are widelyrecognized network protocols. The system architecture of each protocol uses amaster and slave setup, but both still use a centralized control approach attheir core. Initially, Animatics set out to use CANopen for advanced motioncontrol networking by extending it.

"Butwe couldn't break through the master-slave mentality, so we had to create ourown protocol which we call Combitronic," Bigler says.

Combitronictechnology uses a CAN serial port to join Animatics' SmartMotor servos in asystem so that any motor's program can read, write or control any other motorby tagging a local variable or command with the other motor's CAN address. Theresult is that a group of integrated servos become one multi-tasking,data-sharing system without writing a single line of communications code orrequiring detailed knowledge of the CAN protocol.

Thisadvancement allows any single axis to act as master to other axes in thesystem. Each servo is able to access and control all of the motion parametersand I/O in other servo motors. Any axis can use inputs or status registers inany other axis to trigger motion with sub-millisecond response times, exceedingthe abilities of most PLCs to coordinate motion and I/O together.


Toleverage the Combitronic capabilities, a new class of commands has been addedto the Class 5 SmartMotors that create multiple-axis coordinated motionaccessible through one line of code executed in any of the contributing motors.First, the programmer sets a desired "path" velocity and acceleration, and thenissues multiple positions and pertinent axis numbers for a completelycoordinated move resulting in straight-line motion along the direct path.

Cammingand contouring functions have dual trajectory capabilities, so users can add arelative motion on top of cam or contour motions. If there is material on aconveyor and a gantry is being used to synchronize its motion with a movingframe of reference such as a conveyor, users can set up a followingrelationship with the conveyor and perform the motion task in the coordinatesystem of the conveyor as it is moving.

Thesystem is also able to perform other advanced motion functions such as curvefitting capable of adjusting the data set and maintaining system accuracy.

MotorControl

Class5SmartMotors range from a Size 17, or 1.7-inch motor, up to more than 1 hp andtorque up to 700 oz-inch. Each motor offers seven built-in I/O points, and anoptional 10 I/O points can be added.

"With10 motors in a system, there can be up to 170 I/O in the system, and programexecution speed is several times faster than in the past. Many applicationsdon't need a PLC in the machine," says Bigler.

Bigler adds that Combitronic provides the benefits of bothcentralized and distributed control by offering a distributed system where theuser gets to write one program. Users typically favor centralized controlbecause they can write one program that controls everything, which is easier tomaintain. Distributed control is an advantage when parts of the machine aredoing different functions, and users don't need to write a complicated programthat is multi-tasking between the different tasks.

"Whetherthe application is single- or multi-axis, our customers love that they don'tneed the PLC and need just one controller and one program with all of thatprocessing power," says Bigler.

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