Colt Industries Operating Corporation

Davey J Chance

Oliver A Bell, Jr

Randall C Gilleland

A programmable system for controlling machining current magnitude and reducing it in a step function as gap voltage falls indicating gap short circuit condition. A set of off-time numbers are computed and stored in an off-time counter. These numbers are recomputed each time a new on or off time is entered in the pulse generator. The original off-time is the normal cutting parameter. As the gap voltage drops, indicating problems, the off-time starts doubling or increasing in a like manner until it has reached many times its normal duration.

Cut-off protection system for electrical discharge machining apparatus

Included in the circuit are a pair of counter timer circuits, a pair of inverters and a D-type flip flop. The inputs of the counters are tied to a programmable computer buss. A number is loaded into the first counter representative of machining power pulse on-time and a second number is loaded into the second counter representative of machining power pulse off-time. As the first counter counts to 0, the pulse output from the first counter is passed through an inverter to the second counter to enable it. After the second counter counts to 0 there will be provided an output through the second inverter to initiate the operation of the first counter. The pulses which are produced at the termination of each count provide operation of a following flip-flop stage which is toggled to provide on-off time for the machining power pulses to the following power module of the electrical discharge machining apparatus.

Programmable pulse generator for electrical discharge machining apparatus

The servo circuit is operable to monitor gap conditions on any number of working leads up to four at the same time. It further has the capability of responding to high voltage operating conditions and then reducing the gap voltage being sensed to an appropriate level. An analog stage is then employed to pick out the most valuable information being provided from the several gap leads. An amplifier of the FET type is used to provide high input impedance to the circuit. An absolute value circuit is further included which in either polarity will rectify the gap signal back to the positive level.

Servo feed system for electrical discharge machining apparatus

A programmable system for controlling maximum machining current. A current limit is entered into the system together with the on time and off time desired. The system operates to use the entered on-time and current values, but the off time will be modified depending on the maximum current limit possible. This will protect the apparatus when an impossible combination has been entered by the operator. The duty cycle is checked against a maximum level such as 87% or a like upper limit.

Current limit system for electrical discharge machining apparatus

Included in the power supply is an output module connected to the gap which module uses a power FET. This module has its current output and the current to the gap controlled as a linear function of the control voltage applied to the gate of the FET. A suitable input means for the control voltage, includes manually controlled potentiometers, microprocessors, keyboards and the like.

Power output module for electrical discharge machining power supply

A protection system circuit which senses and responds to abnormal gap voltage condition. The circuit is operable in either positive or negative polarity of the gap. The circuit includes two branches, one relating to positive gap polarity and the other to negative polarity. The appropriate one of the two branches is selected by enabling one of two comparators in the respective branches.

Gap condition sensing circuit for electrical discharge machining power

The system includes a standard servo feed arrangement in which responsive to gap voltage, servo feed is controlled for the electrode tool or alternately the workpiece.

Adaptive control of gap voltage and power to control servo operation of

A digitally controlled and free-running multivibrator for the power supply is used to supply machining power pulses of predetermined ON and OFF time duration. The pulse output from the digital multivibrator is passed through at least one intermediate drive stage to trigger an electronic output switch, which is operatively connected both to a main DC power source and the gap, to actually provide the machining power pulses thereto. Responsive to a predetermined drop in gap voltage, a digitally predetermined extended OFF time is added.

Electrical discharge machining power supply with digitally controlled on

An improved high voltage module for use in conjunction with a standard power module. The high voltage module includes a floating power supply in parallel with the standard power module and without ground connection included in the high voltage module are a plurality of stages of Darlington amplifiers. The two modules are opticoupled in the circuit with provision for fast turn-on and turn-off networks for the opticoupling network.

Power supply circuit of the high voltage type for electrical discharge

Gap current is sensed and a voltage signal representative of gap current is integrated to provide a relatively stable DC voltage that is proportional to average current at the gap. A reference setting is made to which the average gap current is compared and, responsive to rise in current above that level, cutoff of the power supply will be initiated.

Protection circuit for electrical discharge machining power supply

The system responds to the frequency of pulses from the pulse generator or multivibrator. As the frequency of the pulses increases, they get closer together and the average voltage changes in a somewhat linear fashion. A final integrator amplifier stage is used to find the predetermined maximum current level for different frequency settings. Responsive to this level being exceeded, machining power is interrupted and the EDM operation interrupted.

Over current protection system for electrical discharge machining

A power supply circuit including a multivibrator and a power output module. Drive signals are provided at low power level and an FET stage is used to provide a high wattage output to operate the power output module. The power output module provides machining power pulses to the gap through a plurality of series resistors so that peak current can be regulated in the module itself.

A set of indicator lights, preferably of the light emitting diode type, are used to provide readout from the gap to indicate a gap open circuit condition, a gap normal machining condition, or a gap short circuit condition, respectively. Three lights are preferably contained in a vertical array to give the operator an exact indication of what type of machining is being carried on and hence inform him as to what correction should be made by way of servo feed adjustment, change of machining current, or the like.

Gap condition light indicator system for electrical discharge machining

The servo circuit is operable both in a dual and in a single mode and includes an analog gate for multiple gap inputs. Dual operation is required where more than one gap is involved such as in the situation where multiple electrodes are carried by a common machine tool ram. In the servo operation, the unwanted information over a relatively wide voltage range is eliminated and the more significant voltage excursions around the 30 volt or gap breakdown voltage level are employed. This compensates for the non-linearity that is inherent in the electrical discharge machining gap.

Servo feed system for an electrical discharge machining apparatus

A servo feed control system providing arc sensing for each individual lead in a multiple lead set up. The lowest arc voltage of the several leads in the system determines the feed of the servo system through a hydraulic servo system or the like. Included are a pair of analog switches one of which is actuated responsive to gap polarity so that the system is conditioned to operate with equal facility at either gap polarity.

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Concord, NC, United States of America

Davey J Chance