Adaptive numerical control apparatus for machine tools

• US 4,408,280 A
• Filed: 10/08/1980
• Issued: 10/04/1983
• Est. Priority Date: 10/11/1979
• Status: Expired due to Term

• Current Assignee: Olivetti Controllo Numerico SPA
• Original Assignee: Olivetti Controllo Numerico SPA
• Inventors: Lauro, Luciano, Bedini, Raffaele, Pinotti, Pier C.
• Primary Examiner(s): Nusbaum, Mark E.
• Assistant Examiner(s): Niessen, William G.
• Application Number:
  US06/195,087
• Time in Patent Office: 1,091 Days
• Field of Search: 364/474, 364/475, 364/167, 364/168, 318/571, 318/561, 318/569, 318/570
• US Class Current: 700/173
• CPC Class Codes: G05B 19/4163 Adaptive control of feed or cutting velocity without NC B23Q15/12
• CPC Class Codes: G05B 2219/49295 Drive spindle motor at maximum, limit torque for rapid machining time

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.

Claims

1. 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.

2. A system as claimed in claim 1, comprising computing means controlled by the control unit for computing the current of said armature circuit corresponding to the power needed by the motor for carrying out cutting-in-air operation, said comparison means being arranged to compare the current sensed by the sensing means and that given by the computing means for excluding the operation of adaptation until such time as the current sensed exceeds the computed current.

3. A system as claimed in claim 1, wherein the said range recording means comprise first means controlled on the basis of the tool characteristics, for defining a band around the limits of the said range, and said means for recording the maximum current include second means controlld on the basis of a predetermined power and torque data of the motor, for defining a band along the maximum current and around the characteristic revolution number of the motor to define an optimum working condition.

4. A system as claimed in claim 3, wherein the comparison means cyclically effect a series of comparisons with the data of the said first and second means for acting on the moving means and on the motor in such manner as first to bring the feedrate and the speed onto the band around the said limits and then to bring them, along the said band, onto the band along said maximum current or around said characteristic revolution number.

5. A system as claimed in claim 4, wherein the comparison means finally condition the moving means and the motor to shift the feedrate and the cutting speed along the band of the said maximum current toward said optimum working conditions for the motor.