machine sychronisation problem

[powerdown]

How can i ensure that 3 machines all ac inverter and shaft encoder controlled will synchronise position from the instant they are called on to run- bare in mind that the machines will stop in different positions.
plc type FX32MR WITH 2 FX2DA OUTPUT MODULES TO THE INVERTERS.
I along with others have tried various programs but at the moment all three machines will take 3/4 machine cycles before thay start runing in synchronisation.
A real brain teaser!!!

 

[wired1]

I'm unfamiliar with the PLC you have. Are you trying to do this strictly with PLC logic or do you have motion control card? If you have a motion card, it should be do-able.

 

[xyzz]

No enough initial data for suggestions.
What is the encoder number of pulses per revolution?
What is the necessary synchronization precision in encoder pulses?
How fast it has to be reached in time units and encoder pulses?
What overrun is allowed?
Is the target speed constant?
What determines the position to be synchonous with?
Why motors are stopped non-synchronized?
Are all the motors driving similar loads or not?
Is each load variable?
Which type inverters are used and how their speed is controlled?
What is accel/decel settings of the invereters?

 

[mdonner]

VFD controlled AC motors are usually not the choice for positioning control applications.
Some type of machines, such as diapers or multy layer cardboard manufacturing, has several motorized feeds and one master pooling motor, when all feeds must reach simultanuously to the bonding line.
This is achived by using a speed proportional analog output signal from the pulling motor to the feeding motor VFDs reference input, with slack detector reference compansation.
Metal millimg machine sometimes have "electrical shaft": you set one motor as master, feed amps proportional analog output as reference to the slave motors whos VFD operate in torque control mode.
Since the nature of the machine dictates the type of solution, more data is required.

 

[dbaird]

Its called "Electronic Gearing" or "Electronic line shafting". Checkout:

http://www.boschrexroth.com/BoschRe...tes/en/products/brc/a_downloads/Packaging.pdf

David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[plcsavvy]

dbaird has it correct. Electronic line shafting is what is required for your application. I would not however recommend using the Indramat servo drives from Bosch Rexroth. These drives are extremely complicated and are over kill for the type of application you are speaking of.These drives can handle interpolation and other advanced applications including CNC. Two years ago I did a project whereby a single turret machine driven by a servo motor was electronically coupled to a discharge conveyor also driven by a servo motor, and a servo driven flow wrapper machine.
The servo drive used to control the main drive motor acted as the "master" The servo drive controlling the discharge conveyor acted as the slave. The slave followed the master at a velocity and phase that was at some proportion to the master servo drive. The master and slave drives communiacted over sercos (fiberoptic) network. The flow wrapper followed an encoder that was attached to the main drive of the single turret machine. The result was that the main drive turret,discharge conveyor, and flow wrapping machine were phase and velocity synchronized. I would recommend that you use one servo drive for the master and the other two as slaves. A major problem arises if each machine has separate low and high level conditions, Which require each machine to stop and start independently.

One major disadvantage I discovered with the indramat system was that the accel and decel ramps are identical.
I discovered that the main drive cluth on the single turret machine would trip when the drive decelerated to a stop.
The solution was to slowly ramp down the analog velocity input to the drive. I referred to this as rampdown speed. when the main drive was required to stop, a signal was sent for a rampdown request to the drive and the analog voltage was gradually reduced. When the desired rampdown speed was reached in the drive, a confirmation signal was sent to the PLC. Upon receiving this signal, the plc then sent the stop signal to the drive, thereby stopping the main turret, and preventing the main drive clutch from tripping.

Best regards, PLCSAVVY