Axis Setup Procedure

The steps below explain how to create and define an axis in the softMC controller.

The following are required:

• Running softMC (actual or simulated)
• User interface (ControlStudio)

Step 1: Declare Axis

In the first line of CONFIG.PRG file write the number of axes that will be in use:

Sys.Naxes = <number>
…
Program
…
End Program

Send this file to softMC and run it by issuing these two lines from terminal window:

send config.prg
reset all

Now you have your axes defined, it is easily to check issuing this command from terminal window:

->?axislist
A1,A2,A3,A4,A5,A6,A7,A8,A9,A10,A11,A12,A13,A14,A15,A16,A17

Step 2: Define Meaningful Axis Name

System default axis names are not very user friendly (a1,a2,a3, etc.). It is a good practice to give them more meaningful names. This is done in CONFIG.PRG file only, by assigning a new name to each axis (no double-quotes) to <axis>.AxisName property.

Sys.Naxes = <number>
…
Program
	a1.AxisName = Xaxis
	a2.AxisName = Lift
…
End Program

Step 3: Prepare General Axis Setup

To set up system axes, a setup program must be prepared. Let’s call it SETUP.PRG.</br> It is important to know:

• To access (write to) an axis property, the axis needs to be attached.
• For some properties, the axis needs to be disabled

SETUP.PRG

Program
	Call SetAxis(a1)
	Call SetAxis(a2)	
	…
End Program

Sub SetAxis(ax as generic  axis)
With ax
	Attach
		En = 0
		…
		<stuff goes here>
		…
	Detach
End With
End Sub

Step 4: Position Units Definition

<axis>.PositionFactor defines the position units that will be used in all position variables of the specified axis (pcmd, pfb, etc.). It consists of:

• Motor encoder resolution seen through the motion bus (See EtherCAT, SERCOS, CanOPEN). How many counts are there in one motor revolution - stored in pos_units global variable (for each axis differently).
• Gear ratio (M:N) and/or the pitch of the linear screw (mm/rev).

• Rotary axes:

For position in degrees PositionFactor is:PFAC = Pos_Units *(M/N)/360

• Linear axes:

For position in millimeters PositionFactor is:PFAC = Pos_Units)/MPITCH

See Motion Bus setup for pos_units and MPITCH setup

Step 5: Direction of Movement

Positive direction of drive's position increments does not have to match the desired positive direction of user axis (Upwards, Left-Right, Counterclockwise). Therefore <axis>.direction flag is to be used:

<axis>.Direction = {1|-1}

Value of -1 indicates direction inversion.

Step 6: Velocity, Acceleration, Jerk Units

Velocity/acceleration/jerk units do not have to match position units. The user may select the units. For all the derivative units (velocity, acceleration, jerk), the default time scale is in milliseconds; therefore scaling is needed.

To use position units per second for velocity the following must be defined:

<axis>.VelocityFactor = <axis>.PositionFactor/1000

In this case if the user sets the position in millimeters the velocity will be mm/sec

To define velocity in RPM of the motor:

<axis>.VelocityFactor = Pos_Units /1000/60

Acceleration and jerk units are the same; their default values are expressed in velocity and acceleration units per milliseconds. Thus, in order to set them per seconds, they need to be set as:

<axis>.AccelerationFactor = <axis>. VelocityFactor /1000
<axis>.JerkFactor        = <axis>. AccelerationFactor /1000

Step 7: Units Summary

Position, velocity, acceleration and jerk units are set by:

<axis>.PositionFactor = …
<axis>.Direction = …
<axis>.VelocityFactor = …
<axis>.AccelerationFactor = …
<axis>.JerkFactor = …

Step 8: Position Limits

Setting position range of an axis. Setting maximum position:

<axis>.Pmax = … and enabling /disabling it: <axis>.PmaxEn = {0|1}

Setting minimum position:

<axis>.Pmin = … and enabling /disabling it: <axis>.PminEn = {0|1}

Setting the axis type:

<axis>.AxisType = 0 ‘ For linear axes
<axis>.AxisType = 1 ‘ For rotary axes

For rotary axes rollover can be defined: Enabling/Disabling it:

<axis>.PositionRollOverEnable  = {0|1}

Setting the whole range:

<axis>. PositionRollOver

Setting the low value:

<axis>. PositionRollOverMin

Note: If the enable flag is not set, the corresponding value does not need to be set.

Step 9: Motion Bus Units

Depending on the type of motion bus (EtherCAT, SERCOS, CANopen) and drive used, several parameters are available for the user to adjust (but are not necessarily needed):

If micro-interpolation is turned on in the drive, the velocity sent to drive must be properly scaled; this is done with (for counts per ms):

<axis>.MotionBusVelocityScale = 0
<axis>.MotionBusVelocityBase = 1

If a limited drive’s position range is used (other then integer 32 bits):

<axis>.CountMin = <drive min position value>
<axis>.CountMax = <drive max position value>

Step 10: Motion Parameters

Motion parameters are grouped into velocity, acceleration and jerk values. All have maximum values for overall limitations, and motion-default values that are used when motion is executed.

Motion default value is:

<axis>.VelocityCruise

Velocity is set according to maximum axis physical limit (drives/motor capabilities and mechanical limitations):

 <axis>.Vmax 

Motion default values are:

<axis>.Acceleration <axis>.Deceleration

Acceleration is set according to maximum axis physical limits (Max drive/motor current, axis load) in user units:

 <axis>.Amax
 <axis>.Dmax

Motion default value is:

<axis>.Jerk

Jerk is the third time-derivation of position, if smooth profiles are used it needs to be defined a good rule of thumb is to set J=BW*A, where J – jerk, A – acceleration, BW- control Bandwidth (Hz).

 <axis>.JerkMax

Step 11: Safety Parameters

Maximum allowed position error (PE). PE is defined as a difference between the position command and position feedback. Due to communication delay of the motion bus and processing time of the drive (micro-interpolation) position command of the several samples before the current is compared to the currently obtained position feedback of the drive:

 <axis>.PositionErrorMax – max allowed position error during in user units.
 <axis>.PositionErrorDelay – number of samples used for delay computation.

Velocity (Runaway) Protection, the feedback velocity of the motor is checked every sample (recommended to be set to 120% of the <axis>.VelocityMax)

 <axis>.VelocityOverSpeed

Sanity Threshold, as a final protection against unintentional jumps (recommended to be set to 1000% of <axis>.VelocityMax):

 <axis>.VelocitySafetyLimit

Torque Error – only if axis dynamic model is turned on

 <axis>.TorqueMaxError

Step 12: Smoothness

Different profile types are available, ranging from very smooth S-curves (Acceleration Trapeze, Sine Acceleration) to less smooth but faster Velocity Trapeze, to totally edgy profiles (Constant Velocity) by setting these two parameters:

<axis>.Smooth defined automatic (0-100) or manual smoothing (-1)

<axis>.PrfType specifies profile more precisely (Velocity Trapeze, Acceleration Trapeze, Sine Acceleration)

Step 13: Axis Setup - Complete Example: the SetAxis Subroutine

sub SetRotAxis(ax as generic axis, byval minval as double , byval maxval as double)
  with ax
    attach
      En = 0
      AxisType = 1
      PositionFactor = pos_unit/360
      VelocityFactor = PositionFactor /1000
      AccelerationFactor = VelocityFactor /1000
      Jerkfactor = AccelerationFactor /1000
      VelocityMax = 1000
      AccelerationMax = 10000
      DecelerationMax= 10000
      JerkMax = 20*amax
      VelocityCruise = 0.5*VelocityMax
      Acceleration = AccelerationMax 
      Deceleration = DecelerationMax
      Jerk = JerkMax 
      PrfType = -1
      Smooth = -1
      VelocityOverspeed = 1.2*VelocityMax
      VelocitySafetyLimit = 10*VelocityMax
      PositionErrorDelay = 2
      PositionErrorMax  = 1
      PositionMax = maxval
      PositionMin = minval
      PositionMaxEn = 1
      PositionMinEn = 1
      PositionRolloverEnable = 0
   detach
  end with
end sub

Step 14: Motion Bus EtherCAT Example

Position Units

First read the motor encoder resolution (MENCRES – SDO:0x20F1:0)

MENCRES = EC_SDO_READ(<addr>,0x20f1,0)

Then set (value of 1) the configured number of motor shaft revolutions and number of driving shaft revolutions. The gear ratio is calculated by the following:

Fieldbus CANopen Gear Motor Shaft Scaling (FBGMS – SDO0x2091:0)

Fieldbus CANopen Gear Driving Shaft Scaling (FBGDS – SDO0x2091:1)

gear ratio = FBGMS / FBGDS

Step 15: Extra - Dynamic Model

Torque Scaling

<axis>.TorqueFactor – according to the Motor KT parameter

Limits

<axis>.TorqueMax – maximum motor torque

Dynamic Model Parameters

axis.DYNAMICMODEL[..] = <…>