Delta Tau GEO BRICK LV User Manual

1.  It can be used as regular feedback to the Turbo PMAC, just as on a servo motor.  In this method, the 

key issue is the resolution and phasing of the encoder edges relative to the steps or microsteps 
produced by the drive – some deadband may have to be created with Ixx64 and Ixx65 to prevent 
hunting at rest.   

2.  The encoder can just be used for position confirmation at the end of moves.  However, this technique 

requires the use of two encoder channels on the Turbo PMAC: one for the simulated feedback of the 
pulse train, and one for the confirmation encoder. 

Stepper-Replacement Servo Amplifiers 
These take position feedback from the servo motor and close all the loops inside the drive.  Do not use the 
encoder signal from the drive for feedback into Turbo PMAC’s servo loop, because the position loops in 
the drive and the controller will conflict with each other.  With these drives, use the commanded pulse 
train from the Turbo PMAC as simulated feedback. 
When using simulated feedback, it is possible to set up the Turbo PMAC servo gains solely with analytic 
methods.  See the Setting up Turbo PMAC2 for Pulse-and-Direction Control section for details.  When 
using real encoder feedback, tune the servo loop just as for an analog velocity-mode drive. 

Hydraulic-Valve Amplifiers 

Hydraulic-valve amplifiers, whether for servo valves or proportional valves, control a fluid-volume flow 
proportional to their command input.  Since fluid flow into or out of a hydraulic cylinder is proportional 
to the velocity of the moving member of the cylinder, the command into the valve’s amplifier is 
effectively a velocity command. 

Several types of amplifiers require the Turbo PMAC servo loop to close the velocity loop as well, making 
the output of this servo loop a torque or force command.  If Turbo PMAC is not doing commutation for 
this motor, the torque/force command is output to the amplifier; if Turbo PMAC is doing the 
commutation, this command is an input to the commutation algorithm.  The main types of amplifiers that 
require the controller to close the velocity loop are: 

• 

Analog-input torque-mode amplifiers 

• 

Sinusoidal-input amplifiers 

• 

Direct-PWM power-block amplifiers 

If the command value from the Turbo PMAC servo loop, regardless of signal type, is a torque or force 
command, the Turbo PMAC servo must close the velocity loop for the motor.  With the standard PID loop, 
this means that the derivative (D) term Ixx31 must be set to a non-zero value.  This derivative action is 
required to get the damping action needed for stability.  Because motors produce a torque or force 
proportional to motor current, the torque/force command out of the servo can also be considered a current 
command. 
There is no need to tune anything in the amplifier with the load attached to the motor, because no 
velocity-loop closure is done in these types of amplifiers.  Any tuning that may be required is dependent 
only on motor properties, so potentially this can even be done by the amplifier manufacturer. 

Analog-Input Torque-Mode Amplifiers 

Analog-input “torque-mode” amplifiers accept an analog voltage that represents a torque/force, and hence 
current, command.  These amplifiers close a current loop inside, and if for brushless motors, perform the 
motor phase commutation as well.  Another name occasionally used for these types of amplifiers is the 
transconductance amplifier, signifying that a voltage input results in a proportional current output.   

Sinusoidal-Input Amplifiers 

A sinusoidal-input amplifier accepts two phase-current commands that are sinusoidal functions of time in 
the steady state.  This type of amplifier expects the controller to calculate the commutation, using the 
torque/force command from the position/velocity-loop servo as the current-magnitude command into the 
commutation.  The amplifier performs the current-loop closure in this style.