Abstract:
A comparative study of 'the vacuum hold-down system and the
electrostatic hold-down system for X-Y plotter was carried out using
fabricated prototype units. The vacuum hold-down system consists of a
motor driven suction unit, suction chamber, perforated flat plotting surface
and pulse-width-modulated motor speed controller. A 24V dc air blower
was converted to an air suction unit with an adjustable pump speed
controlled by a pulse-width-modulated motor speed controller. The holddown
force on the plotting paper for varying pump speed was measured
using gravitational force technique. The graphical analysis (using linear
regression) of the collected data produced a linear relationship between
the measured hold-down force and the pump speed which showed that
the hold-down force is O.004±O.0001 N 5% per 100rpm.
The fabricated electrostatic paper hold down system consists of the
electrostatic charging unit, insulated charged metal sheet and flat plotting
surface. The design of the electrostatic charging unit was based on
voltage multiplication principle with a symmetrical Cockcroft-Walton half
wave voltage multiplier circuit (modified Jacob's ladder circuit) powered by
a high frequency ac voltage source (500V, 12kHz) obtained using dc-ac
voltage inverter circuit. The parallel plate capacitor and the corona
discharge methods were used for charging the insulated plate. The holddown
force on the plotting paper for varying charge , voltage was measured
using gravitational force technique. The' experiment showed that the
measured force varied linearly with the charging voltage with an average
hold-down force of O.003±O.0001 N V-1. The two systems under study were efficient as paper hold-down systems but the vacuum system was
more bulky and it required additional hardware for its implementation.
