Cutter feed rate control system

• US 4,330,832 A
• Filed: 03/07/1980
• Issued: 05/18/1982
• Est. Priority Date: 03/13/1979
• Status: Expired due to Term

• Current Assignee: Fujitsu Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fujitsu Fanuc Ltd (Fanuc Corporation)
• Inventors: Fujioka, Yoshiki, Kawada, Shigeki, Kohzai, Yoshinori
• Primary Examiner(s): Smith, Jerry
• Application Number:
  US06/128,173
• Time in Patent Office: 802 Days
• Field of Search: 364/474, 364/475, 318/571
• US Class Current: 700/173
• CPC Class Codes: B23Q 15/10 to maintain constant cutting velocity between tool and workpiece

Abstract

A method of, and apparatus for, controlling the feed rate of a cutter in a machine tool of the type in which a spindle is rotated by an electric motor having operating regions of constant torque and output characteristics so as to render constant the circumferential speed of a workpiece while the workpiece is subjected concurrently to a machining operation by moving a cutter into contact therewith. The apparatus includes mechanism for computing the maximum cutter feed rate, the circumferential speed V_c of the workpiece, the cutting width d of the cutter and the maximum cutting quantity Q_max which is decided by the maximum power P_max of the motor, mechanism for computing a spindle speed N_s from the circumferential speed V_c and the outer diameter D of the workpiece, mechanism for comparing the magnitudes of a base speed N_b and the spindle speed N_s, where the base speed N_b is defined as a spindle speed at which there is a transition from the constant torque region of the motor to the constant output region thereof, and mechanism for computing the cutter feed rate f_r from f_r.sbsb.max,·N_s and N_b. The cutter is fed at the rate f_r.sbsb.max when N_s ≧N_b and at the rate f_r when N_s <N_b, whereby a cutting operation is performed while utilizing the power of the motor to the fullest possible extent.

Claims

1. In a method of controlling the feed rate of a cutter employed in a machine tool of the type in which a spindle is rotated by an electric motor having operating regions of constant torque and output characteristics so as to render constant the circumferential speed of a workpiece while the workpiece is subjected concurrently to a machining operation by moving a cutter into contact therewith, the improvement comprising the steps of:

storing a maximum cutter feed rate f_r.sbsb.max which is computed from a circumferential speed V_c of the workpiece, a cutting width d of the cutter, and a maximum cutting quantity Q_max decided by the maximum power P_max of the motor;

computing a spindle speed N_s from an equation N_s =V_c /π

·

D where D is the outer diameter of the workpiece;

comparing the magnitude of the spindle speed N_s with the magnitude of a base speed N_b defined as a spindle speed at which there is a transition from the constant torque region of the motor to the constant output region thereof; and

feeding the cutter at the feed rate f_r.sbsb.max when N_s ≧

N_b and at a feed rate which is reduced in conformance with the spindle speed N_s when N_s <

N_b.

2. A method of controlling the feed rate of a cutter according to claim 1, further comprising a step of feeding the cutter at a feed rate f_r which is computed from an equation f_r =f_r.sbsb.max ·

N_s /N_b when N_s <

N_b.

3. A method of controlling the feed rate of a cutter according to claim 1, in which the maximum feed rate f_r.sbsb.max is computed by using an equation f_r.sbsb.max =Q_max /d·

V_c.

4. In an apparatus for controlling the feed rate of a cutter employed in a machine tool of the type in which a spindle is rotated by an electric motor having operating regions of constant torque and output characteristics so as to render constant the circumferential speed of a workpiece while the workpiece is subjected concurrently to a machining operation by moving a cutter into contact therewith, the improvement in said apparatus comprising:

memory means for storing a maximum cutter feed rate f_r.sbsb.max which is computed from a circumferential speed V_c of the workpiece, a cutting width d of the cutter, and a maximum cutting quantity Q_max decided by the maximum power P_max of the motor;

spindle speed computing means for computing a spindle speed N_s from the equation N_s =V_c /π

·

D where D is the outer diameter of the workpiece;

comparing means for comparing the magnitudes of a base speed N_b and the spindle speed N_s, where the base speed N_b is defined as a spindle speed at which there is a transition from the constant torque region of the motor to the constant output region thereof; and

cutter feed rate computing means for computing a cutter feed rate f_r from the equation f_r =f_r.sbsb.max ·

N_s /N_b ;

wherein an output indicative of the maximum feed rate f_r.sbsb.max is obtained when N_s ≧

N_b and an output indicative of the feed rate f_r is obtained when N_s <

N_b so that the cutter is fed at the feed rate f_r.sbsb.max or f_r in conformance with the spindle speed.

5. An apparatus for controlling the feed rate of a cutter according to claim 4, further comprising computing means for computing the maximum cutter feed rate f_r.sbsb.max from the equation f_r.sbsb.max =Q_max /d·

V_c using the maximum cutting quantity Q_max, the circumferential speed V_c and the cutter width d.

6. An apparatus for controlling the feed rate of a cutter according to claim 4, further comprising memory means for storing the distance from the center of the workpiece to the current position of the cutter, the content stored in said memory means being incremented or decremented whenever the cutter moves radially of the workpiece by a prescribed amount and in accordance with the direction of cutter movement, the value of said spindle speed N_s being obtained by utilizing the content stored in said memory means as the value of the workpiece radius.