Emerson Control Techniques Epsilon Eb Series Reference Manual page 37

Epsilon Eb and EN Drives Reference Manual
In applications with un-counterbalanced vertical loads, you must be careful not to set the
controller's torque command to zero when the upper Travel limit is activated. Setting the
controllers analog torque command to zero in this situation will command the axis to move
off the limit switch causing the load to drop.
If your controller removes the torque command (zeroes the analog command output) when a
Travel Limit is activated, you have a number of choices to prevent the load from dropping.
All of which require some external logic to determine when the controller can actually take
control again.
• Activate the opposite Travel Limit input function, then release it when the controller is
operational again.
• Activate the Stop input function, then release it when the controller is operational again.
• Apply the axis brake, then release it when the controller is operational again
Pulse Mode
In applications with horizontal, counterbalanced or un-counterbalanced vertical loads, the
load will be held in position when motion is stopped due to a + or - Travel Limit. The position
will be held until the controller commands motion in the opposite direction of the activated
Travel Limit.
When the travel limits are activated, the drive will decelerate at the Travel Limit Deceleration
Ramp and will continue to store all the command pulses received up to ±2
stored pulses need to be cleared out before the axis will move off the Travel Limit. This can
be done if the controller generates command pulses in the direction opposite the activated
Travel limit. The stored command pulses can also be cleared by activating both Travel Limit
input functions at the same time, activating the Stop input function or disabling the drive for
as little as 5 msec (plus any debounce time).
Torque Limiting
The Torque Command is calculated as shown previously, but its value is limited by the
Torque Limit parameter and the current foldback function (see "Torque Limit" and "Current
Foldback"). The result of this limiting function is Torque Command Actual. This is the
command that drives the Power Stage to generate current in the motor. The Torque Limit
Active output function is active whenever the Torque Command Actual is less than from the
Torque Command. This will be true when motion is stopped due to a Travel Limit input
function.
Torque Limit Function
The Torque Limit Enable input function allows an external controller to limit the Actual
Torque Command to a lower value. The Torque Limit parameter is active only when the
Torque Limit Enable input function is active.
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