ALLEVIATION OF DELAYS AND INACCURACIES IN MACHINING BY THE CONSTANT SURFACE FEET PER MINUTE MODE

• US 3,840,791 A
• Filed: 02/26/1973
• Issued: 10/08/1974
• Est. Priority Date: 02/26/1973
• Status: Expired due to Term

• Current Assignee: William H. Mack
• Original Assignee: William H. Mack
• Inventors: Mack, William H.
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Vandenburg, John P.
• Application Number:
  US05/336,055
• Time in Patent Office: 589 Days
• Field of Search: 340/172.5 235/151.11 318/571,573,574,39
• US Class Current: 318/571
• CPC Class Codes: G05B 19/182 characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control G05B19/21 - G05B19/40 take precedence
• CPC Class Codes: G05B 2219/34391 Synchronize axis movement and tool action, delay action, simulation inertia
• CPC Class Codes: G05B 2219/43007 Acceleration from rest
• CPC Class Codes: G05B 2219/43141 Surface, path, tangential speed
• CPC Class Codes: G05B 2219/43152 Feed in, transfer line, rapid traverse to work, grip speed
• CPC Class Codes: G05B 2219/45136 Turning, lathe

Abstract

Methods and apparatus for causing a turning machine tool to operate with selectable but '"'"''"'"''"'"''"'"'constant surface feet per minute'"'"''"'"''"'"''"'"' (CSFM) under the control of an iteratively computing numerical control director, and characterized by anticipation of the necessary spindle or table r.p.m. which will be required at the start of a cut, such that as the cutter is rapidly approaching a workpiece, the spindle or table is accelerated to that required speed, thereby to substantially eliminate the delay which would be necessary to wait for the required speed to be reached with spindle or table servo motors of limited power driving loads with high inertia. The invention is specifically embodied in methods and apparatus for substituting (in lieu of signals representing the actual radius of the cutter from the workpiece center) signals representing the radial distance from the work center which the cutter will reach at the end of a rapid traverse positioning motion- and while that positioning motion is being executed- in the steps and apparatus by which the table or spindle speed is made inversely proportional to a signaled radius value.

Claims

1. In a machine tool control system having means to drive a spindle at a rotational speed which varies inversely in proportion to the radial distance of a cutter from the spindle axis as the cutter moves to different positions along a path disposed radially of the spindle axis, and wherein the cutter is moved through successive segments to successively commanded end point positions measured from the spindle axis along that path, the improved method which comprises a. signaling successively each successive commanded end point position, and b. when the cutter is to be moved in a positioning mode free of contact with any workpiece on the spindle, energizing said spindle drive means to call for a rotational speed which is inversely proportional to the signaled commanded end point position.

2. The method set forth in claim 1 wherein said spindle is driven by a velocity servo responsive to a commanded speed signal and having response time delays due to inertia, and further characterized in that said step (b) includes supplying to the servo a commanded speed signal which is inversely proportional to the signaled commanded end point position, whereby the spindle may accelerate or decelerate to the commanded speed during the time required for the cutter to reach the commanded end point position.

3. In the controlling of a machine tool having a rotatable spindle and a cutter-carrying member movable along a path radial of the spindle axis and to positions measured from the spindle axis, the method comprising a. producing first or second mode signals (POS or POS), b. driving said member toward a signaled end point position on the path whenever its actual position is not in agreement therewith, c. producing a speed command signal which (i) varies dynamically and inversely with changes in the actual position of said member when said first mode signal exits or (ii) is inversely proportional to the signaled end point position when said second mode signal exits, and d. utilizing said speed command signal to correspondingly control the speed at which said spindle is rotationally driven.

4. In the controlling of a machine tool having a rotatable spindle and a member translatable along a path disposed radially of the spindle, the method comprising a. producing first or second mode signals (POS or POS) designating rapid traverse or feeding modes of translation for the member, b. producing successive sets of end point signals (XCEP) representing successive final positions to which said member is to be moved along said path, c. producing position signals (XCP) which dynamically change to substantially represent the actual position of said member along the path, d. moving said member toward the signaled final position to bring its actual position into agreement with the signaled final position, said moving being (i) at a feed rate when said first mode signal exits or (ii) at a traverse rate when said second mode signal exits, e. driving said spindle at a changing rotational speed inversely proportional to the value (XCP) represented by said changing position signals when said first mode signal exits, and f. driving said spindle at a rotational speed inversely proportional to the value (XCEP) represented by said end point signals when said second mode signal exits.

5. In a machine tool control system having means to rotate a spindle at a variable controlled speed And means to translate a cutter member along an X axis disposed radially of the spindle axis, th method which comprises the steps of a. producing first electrical signals digitally representing the X axis segment end point coordinate (XCEP) to which the member is to be moved with respect to the spindle axis, b. producing second electrical signals digitally representing a dynamically changing commanded X axis coordinate (XCP) to be occupied by the member, c. changing said second signals either (i) at a rapid traverse rate or (ii) at a feed rate so that commanded coordinate progressively changes to approach the end point coordinate, d. utilizing said second signals to control said translating means to move the member along the X axis to keep its actual X axis coordinate position dynamically in agreement with said commanded coordinate, e. producing a changeable speed command signal and energizing said rotating means therewith to drive said spindle at a speed proportional thereto, f. utilizing said first signals to make said speed command signal inversely proportional to the end point coordinate (XCEP) while and when said second signals are being changed at a rapid traverse rate, and g. utilizing said second signals to make said speed command signal change to be dynamically inversely proportional to the commanded X axis coordinate (XCP) while and when said second signals are being changed at a feed rate.

6. In a method of controlling a machine tool having a rotatable spindle adapted to carry a workpiece, and a cutter movable along a path radial of the spindle axis to different positions measured relative to such axis, said method comprising a. measuring off successive, equal time periods Delta T, b. representing by first changeable digital signals successive programmed end point positions XCEP of successive path segments, c. representing by second changeable digital signals successive commanded positions XCP, d. changing said second signals to change the commanded position XCP by an amount Delta X during each period Delta T, where Delta X is proporational to a desired velocity at which the cutter is to be moved, until XCP becomes equal to XCEP, and thereafter signaling a new value of XCEP, e. moving the cutter along the path to keep its actual position dynamically and substantially in agreement with the position XCP represented by said second signals, f. producing a speed command signal which varies in inverse proportion to the commanded position XCP represented by said second signals, and g. applying said speed command signal to a spindle driving servo to rotate the spindle at a speed proportional to that signal, the improvement which comprises i. omitting said step (f) when the cutter is to be radially positioned while free of contact with the workpiece, and instead, ii. producing said speed command signal such that it is inversely proportional to the programmed end point position XCEP represented by said first signals.

7. In a machine tool control system having means to drive a spindle at a rotational speed which varies inversely in proportion to the radial distance of a cutter from the spindle axis as the cutter moves to different positions along a path disposed radially of the spindle axis, and means for moving the cutter through successive segments to successively commanded program end point positions measured from the spindle axis as an origin along the path, the improvement which comprises, in combination a. means for signaling successively each successive commanded program end point position, and b. means for energizing said spindle drive means to call for a speed which is inversely proportional to signaled commanded end point position whenever the cutter is moving in a positioning mode free of contact with any workpiece on the spindle.

8. In a system for controlling a machine tool having a rotatable spindle and a cutter-carrying membeR movable to different positions measured from and lying on a path radial to the spindle axis, said system including a. means for normally driving said spindle at a rotational speed inversely proportional to the radial position of said member as the latter moves along said path, b. means for successively signaling end-point positions to be reached at the ends of successive segments to be moved by the member along the path, and c. means for moving the member at programmed feed rates from one end-point to the next, the improvement which comprises, in combination d. means for disabling said means (a) under predetermined conditions indicative that the cutter is free of contact with any workpiece on the spindle, and e. means operative simultaneously with said means (d) for driving the spindle at a rotational speed inversely proportional to the end point position signaled by said means (b), whereby the spindle will have a speed inversely proportional to actual radial displacement of the member when it reaches said end point position even though the spindle driving means is subject to response delays due to inertia.

9. In a machine tool control system having means to drive a spindle at a variable controlled rotational speed and means to translate a cutter member along an X axis disposed radially of the spindle axis, the combination comprising:

means for producing first electrical signals digitally representing the X axis segment end point coordinate (XCEP) to which the member is to be moved, with the spindle axis taken as the origin of the X axis, means for producing second electrical signals digitally representing a dynamically changing commanded X axis coordinate (XCP) to be occupied by the member, means responsive to a first mode signal (POS) for changing said second signals such that the commanded coordinate (XCP) changes at a feed rate, means responsive to a second mode signal (POS) for changing said second signals such that the commanded coordinate (XCP) changes at a traverse rate, means responsive to said second signals for controlling said translating means to move the member along the X axis and keep its actual coordinate position dynamically in agreement with the changing commanded coordinate (XCP), means for producing a commanded speed signal and applying it to said drive means to cause the spindle to rotate at a speed proportional to that signal, means responsive to the combination of said first mode signal (POS) and said second signals for controlling said producing means to make said commanded speed signal vary to be inversely proportional to the represented changing commanded coordinate (XCP), and means responsive to the combination of said second mode signal (POS) and said first signals for controlling said producing means to make said commanded speed signal inversely proportional to the represented end point coordinate (XCEP).