Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/4155—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by programme execution, i.e. part programme or machine function execution, e.g. selection of a programme
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/416—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control of velocity, acceleration or deceleration
  • G05B19/4163—Adaptive control of feed or cutting velocity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T408/00—Cutting by use of rotating axially moving tool
  • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T408/00—Cutting by use of rotating axially moving tool
  • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
  • Y10T408/165—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor to control Tool rotation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T408/00—Cutting by use of rotating axially moving tool
  • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
  • Y10T408/17—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor to control infeed
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T408/00—Cutting by use of rotating axially moving tool
  • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
  • Y10T408/175—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor to control relative positioning of Tool and work
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T409/00—Gear cutting, milling, or planing
  • Y10T409/30—Milling
  • Y10T409/30084—Milling with regulation of operation by templet, card, or other replaceable information supply
  • Y10T409/300896—Milling with regulation of operation by templet, card, or other replaceable information supply with sensing of numerical information and regulation without mechanical connection between sensing means and regulated means [i.e., numerical control]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T409/00—Gear cutting, milling, or planing
  • Y10T409/30—Milling
  • Y10T409/306664—Milling including means to infeed rotary cutter toward work
  • Y10T409/306776—Axially
  • Y10T409/306832—Axially with infeed control means energized in response to activator stimulated by condition sensor
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T409/00—Gear cutting, milling, or planing
  • Y10T409/30—Milling
  • Y10T409/306664—Milling including means to infeed rotary cutter toward work
  • Y10T409/306776—Axially
  • Y10T409/306832—Axially with infeed control means energized in response to activator stimulated by condition sensor
  • Y10T409/306944—In response to work condition

Definitions

• This invention relates to adaptive control of cutting operations on CNC-operated machine tools in which a controlled input parameter characterizing the movement of a cutting tool relative to a workpiece, is continuously adjusted during a cutting operation in response to a measured output operation parameter defining the productivity of the operation.
• the present invention particularly concerns the adaptive control of turning operations performed on lathes, where the controlled input parameter is a feed rate of the cutting tool and the output parameter is a cutting torque, cutting force or consumed power of the lathe's spindle drive.
• a program instructs a feeding means on a feed rate with which a taming tool should cut a workpiece and instructs the lathe's spindle drive on a speed with which a workpiece associated therewith should be rotated.
• the feed rate and the selected speed are controlled input parameters that are normally fixed by the program for each cutting operation based on pre-programmed cutting conditions such as depth of cut, diameter of the workpiece, material of the workpiece to be machined, type of the cutting tool, etc.
• pre-programmed cutting conditions such as depth of cut, diameter of the workpiece, material of the workpiece to be machined, type of the cutting tool, etc.
• the efficiency of CNC programs is limited by their incapability to take into account unpredictable real-time changes of some of the cutting conditions, namely the changes of the depth of cut, non-uniformity of a workpiece material, tool wear, etc.
• FIG. 3 illustrates a known control system for adaptively controlling a turning operation, for use with a CNC-operated lathe having a feeding means and a spindle drive that are instructed by a CNC program to establish the movement of, respectively, a cutting tool and a workpiece attached to the spindle, with pre-programmed values of respective controlled input parameters F 0 that is a basic feed of the cutting tool and S 0 that is a basic rotational speed of the spindle (the cutting tool and the workpiece are not shown).
• the control system comprises a torque sensor for measuring a cutting torque ⁇ M developed by the spindle drive.
• the cutting torque ⁇ M may have different current values ⁇ M c in accordance with which the torque sensor generates current signals U c proportional to ⁇ Mc.
• the maximal value of the cutting torque ⁇ Mmax is a predetermined cutting torque developed by the spindle drive during cutting with a maximal depth of cut, and the signal transmission coefficient of the amplifier is defined as
• the coefficient A characterizes the extent to which the feed rate F c may be increased relative to its pre-programmed value Fo, and it usually does not exceed 2. Since, as mentioned above, the signal U c is proportional to the cutting torque
• the relationship (1) may be presented, for the purpose of explaining the physical model of the adaptive controller, as follows:
• Ko is a correction coefficient corresponding to the signal transmission coefficient ko of the adaptive controller and it is accordingly calculated as
• the physical model of the adaptive controller is illustrated in Fig. 4. As seen, the change of the cutting conditions B influences the current value ⁇ Mc of the cutting torque which is used by the adaptive controller to determine the coefficient ac characterizing the current value F c to which the feed rate should be adjusted to compensate the changed cutting conditions B.
• c is a static coefficient established for turning operations and ac is defined in the equation (2).
• the cutting torque ⁇ M C may be expressed as:
• the maximal cutting torque ⁇ Mc may be expressed as:
• K Ko- Kc.
• the operation input parameter F is preferably a feed rate of the turning tool and the operation output parameter ⁇ M is preferably a cutting torque developed by a drive rotating the workpiece.
• the operation output parameter may also be a cutting force applied by the tool to the workpiece or a power consumed by the drive.
• the predetermined value ⁇ M o of the output parameter is preferably a maximal value ⁇ M max which this parameter may have when the varying operation condition B differs to a maximal extent from its original or nominal value.
• the invariant correction coefficient component K o is defined as
• Fd being an idle feed and F 0 being a pre-programmed basic feed rate.
• the varying operation condition B may be a mathematical equivalent of one or more physical parameters of the cutting process.
• U 0 is a signal from the sensor of the operation output parameter corresponding to the value ⁇ Mo.
• ⁇ M o ⁇ M ma x and
• the sensor of the output operation parameter ⁇ M is a sensor of a cutting torque developed by a drive rotating the workpiece and the input parameter override unit is a feed rate override unit.
• the correction processing means may comprise a sensor or a calculator for, respectively, sensing or calculating current values of the operation condition B, to be subsequently used in the calculation of k c .
• FIGs. 1A and IB are block diagrams of adaptive control systems having adaptive controllers in accordance with two different embodiments of the present invention
• Figs. 2A and 2B illustrate physical models of the adaptive controllers shown, respectively, in Figs. 1A and IB;
• Fig. 3 is a block diagram of a control system having a known adaptive controller
• Fig. 4 illustrates a physical model of the known adaptive controller shown in Fig. 3
• Fig. 5 illustrates the dependence of the cutting torque ⁇ Mc on the cutting depth he in systems having a known adaptive controller as shown in Figs. 3 and 4 (curve I), and having an adaptive controller according to the present invention (curve H).
• Figs. 1A and IB illustrate two different embodiments of an adaptive control system according to the present invention, for use with a CNC-operated lathe for adaptively controlling a turning operation performed on a workpiece by a cutting tool (not shown).
• the control systems designated as la and lb in respective Figs. 1A and IB each have a feeding means 2 connected to the cutting tool and a spindle drive 4 associated with the workpiece, that are instructed by a program of a CNC unit 6 to establish the relative movement between the cutting tool and the workpiece with pre-programmed values of respective basic feed rate F 0 of the cutting tool and basic rotational speed S 0 of the spindle.
• the feed rate override unit 9 is controlled by an adaptive controller 10 operating on the signal U c from the torque sensor 8 to determine the extent ⁇ F 0 to which the override unit 9 should adjust the feed rate F c .
• the signal transmission coefficient k, or its physical equivalent - the correction coefficient K - is calculated in a manner that takes into account the variation of the depth of cut he.
• the cutting torque ⁇ M c in t irning operations may be expressed in accordance with the equation (4), in which, for the purpose of the present explanation, A is a coefficient characterizing the extent to which the feed rate F c may be increased relative to the pre-programmed value F 0 .
• A/ ⁇ M m a x AKo constitutes a first correction coefficient component Ko which is invariant in time and 1/cFohc constitutes a second correction coefficient component Kc which varies in accordance with the variation of the depth of cut he.
• correction coefficient K may also be expressed as:
• K — ° ⁇ -. (8) It follows from the above that the second coefficient component Kc may be expressed either as 1/cFohc or as ac/ ⁇ Mc.
• the dete ⁇ riination of the correction coefficient K should be performed under the logical conditions that K should not be less than a zero and should not exceed 1/ ⁇ Mma ⁇ .
• Figs. 2a and 2b represent physical models of the determination of the coefficient K, based on the above equations (7) and (8).
• the physical models presented in Figs. 2 A and 2B are implemented by the adaptive controller 10 constructed to determine kUc ⁇ koU c -kcUc, where ko is a predetermined invariant signal transmission coefficient component and kc is a varying signal transmission coefficient component dependent on the depth of cut he.
• the coefficient components ko and kc are determined in the same manner as the correction coefficients Ko and Kc. Namely, the invariant coefficient component ko is determined as
• the adaptive controller 10 comprises an amplifier 14 with the invariant signal transmission coefficient ko and a correction processing means 16 with the varying signal transmission coefficient kc.
• the correction processing means 16 may have either a depth of cut sensor 20a (Fig. la) or a variation calculator of cutting conditions 20b (Fig. lb), and a computing element 22 for deteraiining current values of kcU c respectively based on either equation (9) or equation (10) in accordance with the respective physical models in Figs. 2A and 2B.
• the feed rate of turning tools may be adjusted, taking into account the variation of the depth of cut he, so as to maintain the cutting torque ⁇ Mc as close as possible to its maximal value ⁇ Mmax, in a substantially wide range of the depth of cut, whereby the productivity of the metal-working is increased.
• Fig. 5 This is illustrated in Fig. 5 as well as in the following table showing experimental results obtained with a known adaptive control system and with an adaptive control system according to the present invention:

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• 1999
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