Speed/Torque Select

ALLEN-BRADLEY
ALLEN-BRADLEY
BULLETIN 1336 IMPACT
SPEED/TORQUE MODE SELECT
APPLICATION NOTE # 1336E - 1
June 24, 1997
PURPOSE
The purpose of this document is to provide guidelines for wiring and
control schemes for the Bulletin 1336 IMPACT AC Drive. This document
is to be used as a suggestion only. Users must ensure that installations
meet applicable codes and are suitable for the existing conditions.
WHAT THIS NOTE
CONTAINS
This note describes the setup and application of the Speed/Torque Mode
Select parameter.
INTENDED
AUDIENCE
This application note is intended to be used by personnel familiar with the
hardware components and programming procedures necessary to
operate the Bulletin 1336 IMPACT.
WHERE IT
IS USED
The diagrams, parameter settings, and auxiliary hardware used in this
application note are designed to address specific issues in many different
applications. Some changes by the Users may be necessary to apply the
concepts of this document to a specific application.
TERMS AND
DEFINITIONS
[ ] - indicates a parameter name.
Link - A link is a software connection between two parameters that lets
one parameter receive information from another.
- This represents a source which is a link parameter that
provides the information.
- This represents a destination which is a link parameter
receiving the information.
File - A set of categorically similar parameter groups.
Group - A set of parameters that are similar in feature or function.
Element - A single parameter within a group.
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HIM - Human Interface Module
DESCRIPTION
The Speed/Torque Mode Select parameter is used to choose the
operating mode for the drive. The drive can be programmed to operate
as a velocity regulator, a torque regulator, or a combination of the two.
Refer to the firmware flowchart shown in figure 1.
Figure 1
As shown in figure 1, parameter 68 [Spd/Trq Mode Sel], is used to select
the mode of operation. Zero torque current is allowed when set to (0).
Set to a value of 1, the drive/motor are operated in speed mode. The
torque command changes as needed to maintain the desired speed.
Set [Spd/Trq Mode Sel] to a value of 2 for torque mode. In torque
regulation mode, the drive controls the desired motor torque. The motor
speed will be a result of the torque command and load present at the
motor shaft.
Min and Max mode are selected by values 3 and 4 respectively. These
two modes offer a combination of speed and torque operation. The drive
will automatically switch from speed to torque mode (or from torque to
speed) based on the dynamics of the motor/load. The algebraic minimum
or maximum of speed/torque will be the operating point for the Min and
Max modes.
The Min mode is typically used with positive torque and forward speed
operation, the minimum of the two being closest to zero. The Max mode
is opposite, typically used with reverse speed and negative torque, the
maximum being the least negative (closest to zero).
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Sum mode is selected when [Spd/Trq Mode Sel] is set to a value of 5.
This mode allows an external torque command to be added to the speed
regulators output when desired.
APPLICATION CONSIDERATIONS
SPEED REGULATION MODE
Operating as a speed regulator is the most common and therefore
simplest mode to setup. Examples of speed regulated applications are
blowers, conveyors, feeders, pumps, saws, and tools.
To configure the drive as a speed regulator, set [Spd/Trq Mode Sel] to 1.
Select a speed reference source and program the appropriate link. The
factory default link is [SP An In1 Value] 134
29
[Speed Ref
1]. If left at default, the drive will follow the speed reference of the
SCANport 1 input. Typically this reference will be the potentiometer on
the drive mounted Human Interface Module. Figure 2 shows the drive
operating in speed regulation mode with a step decrease in load. The
response of the drive/motor to a change in load is dependent on the
tuning of the drive (bandwidth setting), and system inertia.
Figure 2
Note that under steady state conditions the speed feedback is steady
while the torque reference is a constantly adjusting signal. This is
required to maintain the desired speed. At transient state, the torque
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reference will change dramatically to compensate for a speed change. A
short duration change in speed is the result of increasing or decreasing
the load very rapidly.
TORQUE REGULATION MODE
A torque regulated application can be described as any process that
requires some tension control. An example of this is a winder or unwinder
where material is being “drawn” or pulled with a specific tension required.
The process requires another element setting the speed.
Configuring the drive for torque regulation requires [Spd/Trq Mode Sel] to
be set to 2. In addition to that, a reference signal must be linked to the
Torque Reference. If an analog signal is used for the reference, link [An
In1 Value] 96
69
[Torque Ref 1].
When operating in a torque mode, the motor current will be adjusted to
achieve the desired torque. If the material being wound/unwound breaks,
the load will decrease dramatically and the motor can potentially go into a
“runaway” condition.
MIN MODE / MAX MODE
This operating mode compares the speed and torque commands, the
algebraically minimum value is used. This mode can be thought of as a
Speed Limited Adjustable Torque operation. Instead of operating the
drive as a pure torque regulator, the “runaway” condition can be avoided
by limiting the speed. A winder is a good example for the application of
the Min Spd/Trq operating mode. Max mode would be used if both speed
and torque are negative.
Figure 3 illustrates how min mode operates. The drive starts out
operating as a torque regulator. The torque reference causes the motor
to operate at 308rpm. The speed reference is 468rpm, so the minimum is
to operate as a torque regulator. While operating in torque regulation, the
load decreases and the motor speeds up. Notice the torque command
has not changed. When the speed regulator comes out of saturation, it
clamps the speed and now the drive operates as a speed regulator. The
At Speed Relay then closes.
Figure 3
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468RPM
308RPM
SUM MODE
Configuring the drive in this mode allows an external torque input to be
summed with the torque command generated by the speed regulator. The
drive requires both a speed reference and a torque reference to be linked.
This mode can be used for applications that have precise speed changes
with critical time constraints. If the torque requirement and timing is known
for a given speed change, then the external torque input can be used to
preload the integrator. The timing of the speed change and the application of
an external torque command change must be coordinated for this mode to
be useful. The sum mode will then work as a feed forward to the torque
regulator.
ZERO TORQUE MODE
Operation in zero torque mode allows the motor to be fully fluxed and ready
to rotate when a speed command or torque command is given. For a cyclical
application where through put is a high priority this mode can be used. When
the [L Option Mode], parameter 116, is set to a value of 19, 20, or 22, logic
inputs may be used to switch between operating modes. Refer to the
Speed/Torque Select Table.
The logic inputs can select zero torque during the “rest” portion of a machine
cycle instead of stopping the drive. When the cycle start occurs, instead of
issuing a start to the drive, a speed regulate mode can be selected. The drive
will then immediately accelerate the motor without the need for “flux up” time.
Speed/Torque Select Table
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SPD/TRQ 1
False
True
False
True
False
True
False
True
SPD/TRQ 2
False
False
True
True
False
False
True
True
SPD/TRQ 3
False
False
False
False
True
True
True
True
OPERATING MODE
Zero Torque
Speed Regulate
Torque Regulate
Min Speed/Torque
Max Speed/Torque
Sum Speed/Torque
Zero Torque
Zero Torque
Zero Torque may excessively heat the motor if operated in this mode for
extended periods of time. No load or flux current is still present when the
drive is operating in zero torque mode. A motor with an extended speed
range or separate cooling methods (blower) may be required.
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