Step / Pulse And Direction Drive - Danaher Motion s200 User Manual

Locking onto the master signal typically takes one-of-three forms. The simplest form just locks the
signals when the master is at rest. As the master begins to move the S200 Position Node is a
slave motor controller that then follows the master per the defined 'gear ratio'. Applications that
require locking onto a moving master can have one-of-two different needs. The first method is a
simple 'velocity' lock. Under this method the drive has been configured to have a discrete input
assigned as the 'lock' (Gearing w/o correction) function. When the input is asserted the drive will
accelerate to the velocity of the moving master and then switch to a full position-mode lock
(pulse-for-pulse) mode. These applications require the velocity of the slave as the main
requirement. The final locking method is slightly more complicated and is used in applications
where the positional relationship to the master signal is as important as the velocity following. A
discrete input is assigned to lock onto the master (Gearing w/ correction). When the input is
asserted the S200 Position Node registers the position of the master and begins accelerating to
the master's velocity but will overshoot the target velocity to 'catch up' to match the position of the
master at the time in which the lock signal was asserted. The S200PN motor overshoots the
master velocity and then decelerates once the lost position was 'made up'. Mathematically
speaking, on a velocity vs time chart, the area under the overshot velocity equals the area lost
during the initial acceleration.
Acceleration and deceleration control in these applications can be a little tricky if the master
speed fluctuates. When locking onto a master at rest you can defeat (set to maximum value) the
ramp control on the S200PN. Locking onto a moving master requires the use of reasonable
acc/dec limits. If the speed of the master can change nearly as quickly as the limits set in the
S200PN then strange results can occur with the slave's lagging response.
To setup the S200 Position node for Gearing:
Drive Setup\Drive Setup; Mode of Operation: Electronic Gearing
Drive Setup \ Gearing; Gearing Type: Quad Encoder
Drive Setup \ Gearing; Electronic Gearing Command Ratio: As desired
Profile Setup; Homing: Auto home, or as desired.
Accel / Decel: As desired but should be set to maximum
I/O Setup \ Digital Inputs: Gearing Active w/ (w/o) Correction
Other settings: As desired
4.3 S / P
TEP ULSE AND
Step and direction control is common in the stepper motor market. Some CNC products (such as
MACH2) also use step and direction command. Some PLCs have step and direction outputs. The
S200 Position Node can make an excellent servo replacement for stepper systems with many
advantages.
Step and direction controllers are motor shaft positioning devices controlled by two signals. One
signal provides the travel direction (An inactive high signal moves the motor clockwise while the
active state moves the motor counter clockwise. More precisely, this signal does not actually
move the motor at all. The second channel called the pulse (or step) channel is the one that
commands motor motion. Each pulse on this channel causes the motor to move one 'pulse' of
motion in the direction commanded by the direction channel. The reason that the motors'
movement of 'pulse' is in quotes is because the actual angular distance of the motor can be
configured by the user. The finer the pulse resolution the smoother the motion and the better the
positioning resolution can be. The S200 Position Node receives the command pulses in on the A
channel and the direction on the B channel of the external encoder input on J12.
It is valuable to bring a mental conceptual view to these applications. The device that generates
the step and direction pulses is a profile generator whose outputs are sent to the S200 PN that
receives these commands into a command position register. It is the S200 PN that contains and
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IRECTION RIVE