Patent ID: 6178081
Filing Date: 2001-01-23
Classification: B23Q

Abstract:
A method of operating an electric permanent chuck comprising the steps of: supplying an alternating current having no more than a single selected frequency and phase from an alternating current source;generating electrical pulses at a frequency equivalent to a multiple of the frequency of the alternating current, the electrical pulses having a predetermined phase relative to the phase of the alternating current;providing an electric permanent chuck having at least one pair of adjacent magnetic coils that are oriented such that the coils within each pair are magnetized by current flow in opposite directions through each respective coil;providing at least one pair of magnetizing SCRs, wherein one magnetizing SCR within each pair is electrically connected to one of the respective magnetic coils within an adjacent pair of magnetic coils and the other magnetizing SCR within each pair is electrically connected to the other of the respective magnetic coils within an adjacent pair of magnetic coils, wherein each magnetizing SCR within each pair has a gate to control communication between each respective magnetic coil and the alternating current source in response to the electrical pulses, and wherein each magnetizing SCR within each pair is configured to allow current to flow in a magnetizing direction through the magnetic coil to which it is connected; andtransmitting a number of electrical pulses to the gate of each pair of magnetizing SCRs, each pulse enabling the magnetizing SCR to which the pulse is transmitted to communicate a charge from the alternating current source to each respective magnetic coil to which the magnetizing SCR is electrically connected to magnetize the respective magnetic coil within the electric permanent chuck, the magnitude of the charge communicated by the magnetizing SCR due to each pulse being a function of the difference in phase between the electrical pulses and the alternating current and the total of all charges communicated to each respective magnetic coil being a function of the number of pulses transmitted to the gate of the magnetizing SCR.