A COMPARATIVE STUDY OF PAPER HOLD DOWN SYSTEMS FOR X-V PLOTTING INSTRUMENTS

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 hold-down 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 hold-down 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.