Lloyd LS1 - Crosshead Drive System; User Limit Switches; Compression Cut-Out

LS SERIES SERVICE MANUAL
ISSUE 4.0 OVERVIEW 10
1.11 Crosshead Drive System
A DC permanent magnet motor moves the crosshead via a gearbox, pulleys, toothed timing belt
and a leadscrew. The motor is powered by a PWM Driver IC, which is fed with a PWM signal
from the Main PCB. The motor speed is controlled by a PWM signal that is generated on the
Main PCB and the value of the PWM is calculated by measuring the speed of the motor encoder
pulses.
1.12 User Limit Switches
The machine is fitted with two mechanically activated limit stops that are fitted onto a vertical
rod mounted on the right hand side of the vertical column. An actuator bar is fitted to the
right hand side of the moving crosshead and this operates the limit stops if the crosshead
moves up or down to touch the relevant stop.
If the crosshead moves up so that the actuator bar touches the upper limit stop, the vertical
limit rod moves up and operates the N/C upper limit switch. If the crosshead moves down so
that the actuator bar touches the lower limit stop, the vertical limit rod moves down and
operates the N/C lower limit switch. Both limit switches (microswitches) are mounted on the
right hand side of the lower casting, under the lower cover.
The machine will stop if one of these switches is operated. An error message will be displayed
on the Full Control Console or an error number will be displayed on the Hand Held Remote.
To reset the machine, accept the error by pressing the ACCEPT key then move the crosshead
away from the limit stop using the appropriate JOG keys.
These stops are provided to prevent the grips from being accidentally driven together.
Therefore, these limit stops should be set to the appropriate position whenever a loadcell and/or
grip are changed.
Please note that these are NOT Cycle limits.
1.13 Compression Cut-Out
The safety compression cut-out load feature is provided by the microprocessor monitoring the
load applied to the loadcell. The machine will stop if a compressive load greater than the user
defined SAFETY JOG LOAD is applied when driving the machine downwards by using either
the down jog key, the return key or during automatic return.
Therefore, it is recommended to manually zero the machine whenever a loadcell and/or
grip are changed.