Movtec XY table driver

This driver controls a Movtec Wacht XY-table using a Nanotec stepper motor controller SMCI33 or compatible serial interface.

This driver implements the sensor interface of the generic data recorder and thus a driver instance can be passed directly to the recorder as a sensor.

Driver configuration

Instantiating the driver requires providing a configuration record of type BRML.Drivers.BioTacCfgT.

 1: 
 2: 
 3: 
 4: 
 5: 
 6: 
 7: 
 8: 
 9: 
10: 
11: 
12: 
13: 
14: 
15: 
16: 
17: 

open BRML.Drivers

let cfg : XYTableCfgT = {
    PortName       = "COM5"   
    PortBaud       = 115200
    X              = { StepperConfig = {Id=1; AnglePerStep=1.8; StepMode=8; StartVel=1000.}
                       DegPerMM      = 360. / 1.25
                       Home          = StepperCfg.Right
                       MaxPos        = 147. }
    Y              = { StepperConfig = {Id=2; AnglePerStep=1.8; StepMode=8; StartVel=1000.}
                       DegPerMM      = 360. / 1.25
                       Home          = StepperCfg.Left
                       MaxPos        = 140. }
    DefaultVel     = 30.
    DefaultAccel   = 30.
    HomeVel        = 10.    
}

PortName is the serial port the drive is connected to, and PortBaud is the corresponding baud rate. Then the parameters of the X and Y axes follow. They are described as follows. Id is the motor id of the axis. AnglePerStep is the angle in degree per motor step. StepMode is the stepping mode of the motor. StartVel is the initial velocity when starting the motor in steps per second. DegPerMM is how many degrees the motor must turn to move the table by \(1\mathrm{mm}\). Home is the direction of the reference switch and can be StepperCfg.Left or StepperCfg.Right. MaxPos is the maximum reachable position in \(\mathrm{mm}\). DefaultVel is the default movement velocity in \(\mathrm{mm}/\mathrm{s}\). DefaultAccel is the default acceleration and deceleration in \(\mathrm{mm} / \mathrm{s}^2\). HomeVel is the homing velocity in \(\mathrm{mm}/\mathrm{s}\).

Driver instance

We can now instantiate the driver.

1: 

let tbl = new XYTableT (cfg)

Initialization and checking of communication is performed automatically. After initialization the driver starts to stream position samples from the XY table.

The driver has overshoot protection and will stop the XY table and terminate the program, if the position of any axis goes below 0 or above MaxPos specified in the configuration. Nevertheless, program and computer crashes can cause a dangerous situation; see the caution below.

The tbl.Home and tbl.DriveTo instance methods return an Async<_> instance. You can perform asynchronous control or pipe all results into the Async.RunSynchronously to perform immediate command execution and wait for the operation to finish before your program continues.

Homing

The XY table must be homed (finding the zero reference positions) before it can be moved. Use the tbl.Home method for that. Homing is only performed, if the XY table is currently not homed.

1: 

tbl.Home () |> Async.RunSynchronously

Reading the current position

The current position is available in the tbl.CurrentPos property. It is a tuple of X and Y positions in \(\mathrm{mm}\)

1: 
2: 

let x, y = tbl.CurrentPos
printfn "The table is currently at X=%.3f mm and Y=%.3f mm." x y

Event-based position acquisition

The driver also provides an event-based interface to obtain position samples. Subscribe to the tbl.PosAcquired event and you will be notified for each newly acquired sample. This is the recommended method if you want to record the position of the XY table or perform closed-loop control (using external sensors).

1: 
2: 

tbl.PosAcquired.Add (fun (x, y) ->
    printfn "Acquired position sample: X=%.3f mm   Y=%.3f mm" x y)

This code will automatically print each new sample as it is acquired.

You can adjust the position sampling interval by setting the tbl.PosReportInterval property to the desired sampling interval in \(\mathrm{ms}\), but changing this property is usually not necessary.

Moving to a target position

To move to a target position with a fixed velocity and linear acceleration and deceleration ramps use the tbl.DriveTo method.

1: 

tbl.DriveTo ((50. (* mm *), 80. (* mm *))) |> Async.RunSynchronously

The first argument is the target XY position in \(\mathrm{mm}\) as a tuple.

You can specify additional arguments for the movement velocity, acceleration and deceleration. If they are omitted, the default values from the configuration are used.

1: 
2: 

tbl.DriveTo ((10. (* mm *), 10. (* mm *)), (5. (* mm/s *), 5. (* mm/s *)), (10. (* mm/s^2 *), 10. (* mm/s^2 *))) 
|> Async.RunSynchronously

Moving with a set velocity

It is also possible to control the movement velocity of the XY table directly. This may be useful when the XY table is to be controlled in a closed loop mode of a larger system.

To enable direct velocity control call the tbl.DriveWithVel method with the desired velocity in \(\mathrm{mm}/\mathrm{s}\) as argument.

1: 

tbl.DriveWithVel ((3. (* mm/s *), 5. (* mm/s *)))

hide *

1: 

Async.Sleep 1000 |> Async.RunSynchronously

Contrary to the rest of the driver interface, this method returns immediately with a unit return type. It does not wait for the XY table to reach the specified velocity.

CAUTION: If the program crashes in a disadvantageous way or the whole computer crashes or the communication is lost, the XY table will continue to move with the last set velocity and crash into the stop. The only way to stop it in such a situation, is to cut the power of the motor driver.

The movement velocity can be adjusted at any time by calling tbl.DriveWithVel again with the new velocity. Use negative velocities to reverse the movement direction. You can optionally specify an acceleration that should be used to acquire the new velocity.

1: 

tbl.DriveWithVel ((-10. (* mm/s *), -20. (* mm/s *)), (7. (* mm/s^2 *), 7. (* mm/s^2 *)))

To stop the table call the tbl.Stop method, optionally specifying the deceleration.

1: 

tbl.Stop ()

The method does not block until the XY table has stopped.

Disposing

Dispose the driver instance after usage.

1: 

tbl.Dispose ()

This will stop the table and release the serial port.

• BRML Drivers
• Home page
• Get Library via NuGet
• Source Code on GitHub
• Release Notes
• Data Recorder
• Usage
• Instrument Drivers
• Linmot
• XY table
• BioTac SP
• Documentation
• API Reference