US 4,408,280 AGranted

Adaptive numerical control apparatus for machine tools

AssigneeOlivetti Controllo Numerico S.p.A.

InventorsRaffaele Bedini, Luciano Lauro, Pier C. Pinotti

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Abstract

The system is applied to a lathe and allows control of the machine to be adapted in such manner as to make use of the maximum power of the spindle motor with the maximum feed of the tool and the minimum cutting speed. The feed rate and the cutting speed are defined by the programmer only as the permitted region within which these parameters must jointly lie. The control unit tends constantly to command the feed rate and the spindle motor in such manner as to be within this region. Then the control unit compares the power consumed by the spindle motor, which is detected by a circuit through the armature current, with the maximum power of the motor for the actual working conditions and tends to cause the feed rate and the number of revolutions to be adapted in such manner as to make use of this maximum power. The system is adapted to exclude adaptation during cutting-in-air operation.

An adaptive numerical control system for a lathe, comprising a cutting tool having optimum cutting conditions when cutting at a predetermined cutting speed and at a predetermined feed rate, a direct-current electric motor operable for rotating a workpiece spindle at a number of revolutions per-unit-time corresponding to an actual cutting speed, said motor having an armature circuit absorbing an electric current proportional to power supplied by the motor, said motor having a predetermined characteristic revolution number defining the optimum working conditions for the motor when the motor operates at the maximum torque and at the maximum power corresponding to a maximum current that said armature circuit can absorb, moving means for moving said tool at the actual feed rate with respect to the workpiece spindle, memory means for storing a machining program, a control unit for executing the machining program stored in said memory means to command said moving means and said motor, recording means for recording a machine technological range around said optimum cutting conditions, said range being defined by maximum and minimum feed rate of said tool, maximum and minimum number of revolutions per-unit-time of said motor and maximum and minimum feed per revolution, said range including said optimum working conditions, said recording means also recording said maximum current and said characteristic revolution number, means for sensing said moving means to indicate the actual feed rate, a tachometer for indicating the number of revolutions per-unit-time of said motor,

a shunt arranged in series with said armature circuit,
shunt sensing means for sensing said shunt to indicate the current flowing in said armature circuit, timing means for defining an optimization cycle, comparison means controlled by said timing means for cyclically effecting a comparison of the actual feed rate indicated by said means for sensing the moving means and the number of revolutions per-unit-time indicated by said tachometer with said range to condition said control unit to command an operation of said moving means and of said motor to first bring the actual feed rate and number of revolutions per-unit-time within said range,
said comparison means being effective when said actual feed rate and number of revolutions per-unit-time are within said range for effecting a comparison of the current indicated by said shunt sensing means and the number of revolutions per-unit-time indicated by said tachometer with said recorded maximum current and characteristic number of revolutions respectively to condition said control unit to command an operation of said moving means and said motor to bring said actual feed rate and said number of revolutions per-unit-time toward said optimum working conditions.

Abstract

Claims5