HS50_advance_level 2.pdf - 第150页
07/2002 Editio n Student G uide HS -50 Advanc ed II 6 Cont rol & C ommun icatio n 20 %DO ODVW& LUFXLW The kineti c ene rgy , s tored i n the m otor and l oad is f ed bac k into th e power supply unit during b …
Student Guide HS-50 Advanced II 07/2002 Edition
6 Control & Communication
19
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This system consists of the following. The ’mailbox’ is used to store the position of the axis re-
quired by the machine controller (the ’Target’ position). The ’Target’ position and the actual posi-
tion, given by the position detection system, are supplied to a comparator, which compares the 2
inputs. The result is supplied to the ’Position Controller’, which outputs the required parameters
for the axis movement.
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This system takes the output from the ’Position Controller’ and the input from the speed detection
system and compares them. This results in a speed requirement, which is fed to the servo card.
The digital signals are converted into an analogue output by a DAC. There are actually 2 outputs,
firstly the V nom, which directly controls the speed and direction of the movement. Secondly there
is the force output, which is used for the initial acceleration of the X & Y axis on S2x machines.
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With a rectifier we generate an appropriate constant DC-Voltage for the power semiconductor of
the axis servo amplifier. The power semiconductor on the DC servo board varies the DC-voltage
according to the speed the motor should move. If the motor should reverse the polarity is changed.
The power semiconductor on the AC servo board sets the voltage so that a sinusoidal motor cur-
rent moves the AC-motor. If the motor should speed up the frequency is increased. If the motor
should reverse the phase sequence is changed.
Power supply DC Axes
+
+ / -
AC from
Transformer
Constant DC
Motor DC
current
accordin
g
turning direction
AC from
Transformer
Constant DC
Sinusoidal
motor curren
t
+
Power supply 3 phase AC axis
07/2002 Edition Student Guide HS-50 Advanced II
6 Control & Communication
20
%DOODVW&LUFXLW
The kinetic energy, stored in the motor and load is fed back into the power supply unit during brak-
ing by the servo amplifier. In the case of large moments of inertia the energy take-up of the filter
capacitors in the power supply units is inadequate, and the servo amplifier would be isolated dur-
ing breaking. To prevent this from happening the ballast circuit absorbs the remaining energy and
ensures correct braking via the servo amplifier.
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The servo amplifier is used as final controlling element for the actual speed of the axis drive. It
attempts to adjust the motor voltage so that the system deviation between specified setpoint
speed and tacho-generator feedback is as small as possible. For force control a power controller
is available. The power controller (current sensor mode) is only used with the Z-axis, when com-
ponents are being mounted with higher placement force (the minimum z-axis force is defined by
the spring loaded sleeve).
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This system compares the setpoint speed requirement, given by the axis controller (V nom) with
the actual motor speed given by the tacho generator fixed to the motor shaft. The tacho generator
generates a voltage, which is directly proportional to speed; the faster the motor turns the higher
the generated voltage. The amount of tacho voltage feed back into the system can be controlled
by adjustment of the tacho potentiometer on the servo card. Therefore motor speed can be directly
affected by adjustment of the tacho potentiometer. The P-gain of this RPM-controller is adjusted
to control the positioning quality of the axis. Therefore you check can the positioning quality ac-
cording to the size and the amount of overshoots after crossing the target position for the first time.
Basic DC-Servo Card Function
Analogue
control signals
from Axis card.
RPM Controller
with Comparator
Motor Control
System
Motor Current
control loop
with Comparator
Controlled
voltage to
motor.
V Nom
V Force
Tacho Adjustment
P Gain Adjustment
Motor
Tacho
Power supply
Student Guide HS-50 Advanced II 07/2002 Edition
6 Control & Communication
21
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The output of the RPM controller produces the set point value for motor current controller loop.
The output of the servo system is fed back current controller loop in order to control the limit of the
motor current. An additional element is the input of the force voltage from the axis controller, which
is used to provide the current limit for the axis movement. An additional element for the X & Y axis
is the (additional) speed signal given by the force input of the servo amplifier to boost the accel-
eration and deceleration. Fixed value resistors limit the maximum motor current and they are
specified by the motor data.
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Here the motor current is controlled to directly affect the motor speed. The output signal of the
current controller is amplified here and fed to the power semiconductors to generate the motor
current. (See Power supply).
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NOTE
The AC Servo card produces the 3 phase AC voltage from the DC voltage inputted into the card.
The third
current signal
is generated on
servo board:
0 - I
L1
- I
L3
= I
L2
Inverter
+
-
+
-
current controlling signal input I
u
/ I
w
current pulse
limiter
I RMS current
limiter
current
commutation
controller
pulse-
witdth-
modulation
over- under
voltage
over current
power stage
operational
controlling
and error logic
2 current controller
Enable start enable
controlling dynamic brake
power supply
readyt
Servo ON
I RMS
error
fatal
error
Inverter