LIBRARY ı6ıul 0) - Cranfield University

the torch end. Only one degree of freedom was implemented, allowing correction of
contact tip-to-workpiece distance (stand-off), when the flat welding position was
used. The moving table was not a complete solution to the problem, since deviations
in the path, apart from stand-off, could not be controlled. Three degrees-of-freedom
would provide a good level of controllability but it would require a seam-tracker,
which was not available.
The implemented sliding table consisted of a moving horizontal platform,
which could be moved vertically by means of spinning a ball nut screw (see Figure
5.2). This movement was provided by a stepper motor (RS Catalogue No. 440-442),
which was driven by a 2A unipolar drive (RS Catalogue No. 332-082) and controlled
by a TRIO Motion Co-ordinator 2 controller. A linear resistive sensor was used to
measure the position of the table relative to an adjustable "zero" position, which was
set by subtracting the output of the resistive sensor from an adjustable voltage signal
(0 volts to 10 volts). The result of this subtraction was used as a measurement of the
table position.
The TRIO Motion Co-ordinator 2 controller' is a multitasking multiaxes
controller which can be programmed by a dedicated BASIC language. The controller
has sixteen 24V digital inputs, of which 8 can also be used as outputs. It can be
connected to a personal computer via RS-232 serial communications and can control
up to 12 axes. The controller used had 4 stepper motor daughter boards installed, of
which only one was used.
Specification of moving table components:
Ball nut screw:
" Diameter:
" Pitch:
" Length:
Stepper Motor:
" Number of steps:
" Maximum torque:
14mm
5 mm/revolution
300 nun
200 steps
" Maximum pull-in speed: 1000 Hz
" Rotor Moment of Inertia: 115 gr/cm2
34 Ncm (300 to 500 Hz) (see Figure 5.4)
The stepper motor drive used could only generate full steps.
Stepper motor + ball nut screw + moving table:
" Resolution:
" Load capacity:
" Travel range:
" Maximum speed:
" Maximum acceleration rate at 20 mm/s:
' Trio Motion Technology Ltd, UK
118
0.025 mm/step
7.0 kg
140 mm
20 mm/s
494 mmis2