Galil Motion Control DMC-4123 - Voltage Drive; Current Drive

1. Voltage Drive
2. Current Drive
3. Velocity Loop
The operation and modeling in the three modes is as follows:
Voltage Drive
The amplifier is a voltage source with a gain of K
v
[V/V]. The transfer function relating the input voltage, V, to the
motor position, P, is
  
 
P V K K S ST ST
V t m e
  1 1
where
T RJ K
m t

2
[s]
and
T L R
e

[s]
and the motor parameters and units are
K
t
Torque constant [Nm/A]
R Armature Resistance Ω
J
Combined inertia of motor and load [kg m
2
]
L Armature Inductance [H]
When the motor parameters are given in English units, it is necessary to convert the quantities to MKS units. For
example, consider a motor with the parameters:
K
t
= 14.16 oz - in/A = 0.1 Nm/A
R = 2 Ω
J = 0.0283 oz-in-s
2
= 2 * 10
-4
kg . m
2
L = 0.004H
Then the corresponding time constants are
T
m
= 0.04 sec
and
T
e
= 0.002 sec
Assuming that the amplifier gain is K
v
= 4, the resulting transfer function is
P/V = 40/[s(0.04s+1)(0.002s+1)]
Current Drive
The current drive generates a current I, which is proportional to the input voltage, V, with a gain of K
a
. The
resulting transfer function in this case is
P/V = K
a
K
t
/ Js
2
where Kt and J are as defined previously. For example, a current amplifier with K
a
= 2 A/V with the motor
described by the previous example will have the transfer function:
P/V = 1000/s
2
[rad/V]
Chapter 10 Theory of Operation ▫ 156 DMC-41x3 User Manual