ON-MACHINE BALLBAR SYSTEM AND METHOD FOR USING THE SAME

Abstract: A ballbar socket head (302) is attached to a standard tool head (304) for a CNC machine tool or like device. The socket head can then be parked on the machine tool's tool chain (316) and selectively loaded into the machine tool's spindle (318) under program control by an automatic tool change arm (320). The ballbar socket head (302) is then engaged with a telescopic ballbar attached to a base socket (308). The ballbar and base socket (308) may be peripherally located on the machine's table (310), or automatically placed on the table for test purpose by the machine tool. The ballbar test function may be automatically performed during loading and unloading of the machine, in between production runs, at downtimes, or at periodic predetermined time intervals. When the ballbar equipment is loaded, the machine tool automatically follows a predetermined controlled-motion pattern for a ballbar test. After the test, the ballbar socket head (302) is returned to the machine's tool chain (316) and the ballbar, and the base unit bar and and ballbar are moved, if appropriate. The results of the test are received by a computer and may be displayed for the operator, stored for statistical analysis, or used dynamically to recalibrate the machine's motion control. Preferably, the ballbar sensor (314) communicates with the computer using wireless methods.

Description: ON-MACHINE BALLBAR SYSTEM AND METHOD FOR USING THE SAME Field of the Invention This invention relates to improved machine accuracy monitoring systems and methods for use with computer numerically controlled machine tools, coordinate measuring machines (CMMs) robots, assembly systems, and the like. Background of the Invention In the past, machine tools have been tested with devices that are selectively set up on the machine in an infrequently performed manual testing process. Figure 1 shows a known telescoping magnetic ballbar test gage for determining the accuracy of machine tools, of a type described in U.S. Patent 4,435,905 to Bryan. Two gage balls (10, 12) are held and separated from one another by a telescoping fixture which allows them relative axial motional freedom but not relative lateral motional freedom. The telescoping fixture comprises a parallel reed flexure unit (14) and a rigid member (16, 18, 20, 22, 24). One gage ball (10) is secured by a magnetic socket knuckle assembly (34) which fixes its center with respect to the machine being tested. The other gage ball (12) is secured by another magnetic socket knuckle assembly (38) which is engaged or held by the machine in such manner that the center of that ball (12) is directed to execute a prescribed trajectory, all points of which are theoretically equidistant from the center of the fixed gage ball (10). As the moving ball (12) executes its trajectory, changes in the radial distance between the centers of the two balls (10, 12) caused by inaccuracies in the machine's motion are determined or measured by a displacement transducer, such as a linear variable differential transformer (LVDT) assembly (50, 56, 58) actuated by the parallel reed flexure unit (14). Measurements can be taken for multiple trajectories about several different fixed ball ( 10) locations, thereby determining the accuracy of the machine. An improved telescopic ballbar system known as SERVCHECK™, sold by Automated Precision, Inc., 7901-C Cessna Ave., Gaithersburg, Maryland, is shown in Figures 2a and 2b. The SERVCHECK™ telescopic ballbar unit 202 uses a parallel spring suspension to provide an extremely accurate and low friction measurement to evaluate the performance of computer-numerically-controlled (CNC) machine tools (MTs), which may include machining centers, milling machines, turning centers, lathes and grinders, CMMS, robots, and multi-axis servo-systems. Unlike the Bryan design, the ballbar has one sphere attached to it. This works with a fixed sphere magnetically attached to the machine table and provides a similar function to that of the Bryan device, but makes the ballbar setup much simpler. This telescopic ballbar transmits signals via wire 203 to an interface module 204, which provides ballbar output data to Winner™ 2.01 SERVCHECK™ software operating on an IBM- compatible personal computer 206. This software records any deviations from a perfect circular path executed by the machine and provides menu driven analysis, online help, interactive setup, and a graphical display. However, earlier ballbar systems of these types were designed for use only during machine calibration certification or maintenance procedures, and required that the machine be taken out of production and set up for the machine accuracy test performed by the ballbar system. The inventor has determined that there is a need for a ballbar system that can be installed as part of the machine and automatically operated on a regular basis to verify accuracy of the machine's servo positioning. Summary of the Invention Therefore, it is a general object of the invention to provide an automatic test gage for determining the accuracy of a numerically controlled machine tool and/or calibrating the machine tool, where the gage is installed as a dedicated tool on the tool changer of the machine tool. It is another object of the invention to provide an improved ballbar system for installation as a dedicated tool on the tool changer of a CNC machine tool, or similar machine or mechanism. It is a further object of the invention to provide an improved method for evaluating a CNC machine tool or a similar machine or mechanism using an automated on-machine ballbar system. Another object of the invention is to provide an improved ballbar system which wirelessly transmits relative position information to a monitoring computer. These objects, and others which will be apparent to those skilled in the art upon reviewing the specification and claims, are achieved in a preferred embodiment by attaching a ballbar socket head to a standard tool head for a CNC machine tool or like device. The socket head can then be parked on the machine tool's tool chain and selectively loaded onto the machine tool's spindle under program control by an automatic tool change arm. The ballbar socket head is then engaged with a telescopic ballbar attached to a base socket. The ballbar and base socket may be peripherally located on the machine's table or automatically placed on the table for test purposes by the machine tool. The ballbar test function may be automatically performed during loading and unloading of the machine, in between production runs, at downtimes, or at periodic predetermined time intervals. When the ballbar equipment is loaded, the machine tool automatically follows a predetermined controlled-motion pattern for a ballbar test. After the test, the ballbar socket head is returned to the machine's tool chain and the ballbar and the base unit and ballbar are moved, if appropriate. The results of the test are received by a computer and may be displayed for the operator, stored for statistical analysis, or used dynamically to recalibrate the machine's motion control. In another preferred embodiment, the ballbar sensor communicates with the computer using wireless methods so that wires do not interfere with the automatic placement and stowage of the ballbar socket. Brief Description of the Drawings Figure 1 is a diagram of a telescoping magnetic ballbar test gauge according to the prior art; Figure 2a is a picture of an improved telescopic ballbar system previously developed by the inventor, and Figure 2b is a view of this ballbar system and an associated computer connected to analyze the output of the ballbar; Figure 3 is a side view of an on-machine ballbar system according to the present invention; Figure 4 is an assembly drawing of one embodiment of a fixed ball mount according to the present invention; Figure 5 is a side view of a fixed ball mount according to the present invention including a ballbar support member; Figure 6 is a flowchart showing the steps of an automated CNC machine ballbar measuring operation according to the present invention; and Figure 7 is a diagrammatic representation of a control system and feedback loop used in the present invention. Detailed Description of the Preferred Embodiments The present invention provides a novel ballbar system for use with a computer numerically controlled (CNC) machine tool or the like, and a novel method for using this system. Referring first to Figure 3, the on-machine ballbar system of the present invention includes a standard ballbar socket head 302 mounted on a standard tool holder 304 of CNC machining center 306; a low-profile, self-centering base mount 308 connectable to the machine table 310; a fixed sphere 312 on base mount 308; and a ballbar sensor 314, with ball on one end and socket on the other. Socket head 302 is a standard ballbar fixed socket, available from Automated Precision, Inc. of Gaithersburg, Maryland, and is mounted on a standard tool holder 304 with a configuration appropriate to machining center 306. Socket head 302 can then be treated as a standard tool of machining center 306. Socket head 302 can be parked on tool chain 316 and then selectively loaded into machine spindle 318 under program control by tool change arm 320. Base mount 308 may be a low-profile, self-centering (6 point semi-kinematic) base mount device installed on the machine table or pallet. This device may be installed below the work zone to avoid interference with part loading. Base mount 308 may also be provided with locating pins and a quick release clamp to allow an operator to manually locate base mount 308 on table 310 when ballbar operation is desired. Fixed sphere 312 is a 1 " diameter fixed sphere with a matching semi-kinematic magnetic coupling for attachment to base mount 308. The magnetic semi-kinematic design allows a highly repeatable positioning of fixed sphere 312 onto base mount 308 in either manual or automatic fashions. If desired, the fixed sphere can also be used with an on-machine touch probe to check for machine repeatability and thermal drift. Ballbar sensor 314 may be a conventional SERVCHECK™ brand ballbar system, sold by Automated Precision, Inc., 7901-C Cessna Ave., Gaithersburg, Maryland, but may also be modified in the manners described herein to facilitate automatic placement procedures and wireless operation. In a first embodiment, ballbar sensor 314 is coupled by wire 322 to a ballbar interface module 204, and from interface box 204 to a computer 206 (both shown in Figure 2b) for processing ballbar output data. Computer 206 preferably runs Winner version 2.01 analysis software, also available from Automated Precision, Inc., 7901-C Cessna Ave., Gaithersburg, Maryland. Figure 4 shows another embodiment of the fixed sphere and associated mounting generally as a unit 400. In this embodiment, a fixed sphere 402 and an auxiliary fixed sphere 404 are attached to a rod 406 and mounted to base 408 by machine screws threaded through holes 409. Base 408 has mounting holes 410 which receive quick-release screws so that an operator can attach unit 400 to the machine table at a predetermined location. Referring now to Figure 5, in another, preferred embodiment, fixed ball 312 may be attached by rod 512 to a base 502 having locating pins 504 and a magnet 506. Locating pins 504 mate with corresponding holes 508 at predetermined locations on machine table 310, and magnet 506 holds base 502 against machine table 310 during the test procedure. In this way, fixed ball 312 and its base 502 can be placed automatically on the table by tool change arm 320 of machine 306. In this embodiment, to facilitate automatic placement of ballbar sensor 314, ballbar sensor support 510 is connected to rod 512. Ballbar sensor support 510 comprises arm 514, pad 516, and an optional spring member 518. Arm 514 is attached to rod 512 and pad 516 is attached to the end of arm 514. Pad 516 is shaped to engage and support ballbar sensor 314 and is preferably provided with a cushioned surface, such as foam rubber, to protect ballbar sensor 314 from damage during placement on pad 516. Pad 516 and arm 514 are arranged so that ballbar sensor 314 is supported slightly below horizontal axis 518. As a result, when ballbar sensor 314 is in a horizontal operational position, it will not contact ballbar sensor support 510 during its rotation about fixed ball 312. Preferably, ballbar sensor 314 is supported by pad 516 at an angle θ of from about 10 degrees to about 40 degrees below horizontal. Optionally, a spring member 518 can be provided to further compensate for possible vertical axis errors in automatic placement of ballbar sensor 314 by the tool changer. In this embodiment, arm 514 is pivotally attached to rod 512 and relatively stiff spring member 518 absorbs shock and allows slight rotation of arm 514 when receiving ballbar sensor 314. Alternatively, arm 514 can be firmly affixed to rod 512 and made flexible (springy) to provide the same function. The on-machine ballbar provides the CNC machine tool operator with a robust, precise, and informative tool to determine the machine's accuracy performance on a routine basis. The operation is quick and transparent to the operator, with minimal operator intervention required. A modified ballbar can also be provided for checking thermal and compliance errors. Optionally, the ballbar can be combined with a spindle (such as a five-axis spindle) to monitor thermal growth and repeatability. Real Time Error Compensation technology can be applied to the CNC machine control operation based on the results of periodic ballbar testing during production runs. In this way, the results of ballbar testing can be used to modify control functions of the CNC machine. For example, if the ballbar test detects a scale mismatch in movement of the CNC machine in the x direction, the movement command signals to the servo motor in the x direction can be modified to compensate for the detected scale mismatch, thus effectively providing a feedback control system for overcoming movement inaccuracy problems of the CNC machine. Although the ballbar may be connected by wires to an interface and thus to a computer for storing and analyzing output information from the ballbar, in a preferred embodiment wireless communication may be provided between the ballbar and the computer interface to avoid interference of the wires with machine operation and automatic placement of the ballbar, as shown in Figure 5. The wireless communication can be performed in any desired band, such as infrared, visible light, microwave, or radio frequency bands. Low power radio freqency transmission has the advantage that the movement and rotation of the CNC machine will not block these transmissions as it may with the light or IR methods, unless multiple light transmitters or receivers are used. Environmental considerations may also dictate placement of the interface box out of the line of sight to the ballbar sensor. In this embodiment, a conventional compact, low power radio frequency transmitter using any desired and available transmission frequency, such as frequencies available for remote control, garage door, or cordless telephone transmissions, is provided in the housing of the ballbar sensor. A battery power supply is also provided in the housing of the ballbar sensor. In situations where the interface box can be placed in a line of sight to the ballbar sensor, infrared transmissions may be preferred. In this case, a plurality of infrared emitters 520 are placed on the outside of the ballbar sensor, positioned so that at least one emitter output can always be received by an infrared emitter detector at the interface box. For example, emitters may be placed to transmit in a plurality of directions, on the top, bottom, and/or sides of the housing of ballbar sensor 314. Referring now to Figure 6, the ballbar setup and test programs are preferably integrated into the machine's auto-cycle. A preferred automatic procedure for setting up and running the on-machine ballbar test program is shown in flowchart form. In the first step, shown in block 602, the ballbar socket with its associated tool holder, the fixed ball, and the ballbar sensor are loaded into the machine tool chain as tools. In the case of the fixed ball and the ballbar sensor, a pickup tool for picking up and placing these items may be provided, and the fixed ball and ballbar sensor may be located near the machine table where the CNC machine can pick them up and place them for operation, using the pickup tool. The pickup tool may have magnetic, clamping, or other mechanisms for engaging the items to be moved. In block 603, it is determined whether it is an appropriate time for running an on-machine ballbar test. For example, such tests may be run during loading and unloading of the machine, in between production runs, at downtimes, or at periodic predetermined time intervals. When a test is to be run, control is transferred to block 604. In block 604, at the beginning of each ballbar test procedure, the fixed ball is placed on the table surface at a specified location and orientation, either directly or through a pickup tool in the machine chain as noted above. In block 606, the ballbar sensor is placed on the fixed ball previously located on the machine table and left resting on a supporting device such as ballbar sensor support 510 (illustrated in Figure 5). Preferably wireless communications are used, but alternatively a wire can be provided in a manner to avoid tangling during automatic installation, or less preferably the wire can be manually installed by an operator. Next, in block 608, the ballbar socket and its associated tool holder are loaded to the machine spindle. In block 610, a ballbar NC setup program is executed to drive the socket to engage the ball end of the ballbar sensor and raise it to a position (e.g. horizontal or vertical) ready for test functions. In block 612, a standard ballbar NC test program is executed to collect ballbar data. The data are automatically analyzed and preferably downloaded to a statistical process control system for the machine or factory. In block 614, the ballbar tools (fixed ball, ballbar sensor, and socket) are removed from the machine work area and/or put back in the machine tool chain as appropriate. The tools are put back in the reverse order of their installation. Finally, in block 616, the results of the ballbar analysis can be used to modify machine control parameters to compensate for any irregular operation. Although less preferred, a similar partly automatic, partly manual procedure may also be performed, as follows: (i) load the socket (with tool holder) to the machine spindle; (ii) manually load the fixed sphere to the base mount; (iii) execute ballbar setup NC program to drive the socket to the ready position; (iv) manually install the ballbar reed between the socket and the fixed sphere; (v) manually connect the ballbar cable to the interface box; (vi) execute the standard ballbar test NC programs; (vii) automatic ballbar data analysis and down loading results to the SPC system; and (viii) remove and unload the ballbar system from the machine. Figure 7 shows a preferred embodiment of the invention wherein a ballbar sensor interface module (SIM) 204, ballbar analysis software 702, and a parameter adjustment module 705 are installed in a personal computer 206. In this embodiment, module 204, ballbar analysis software 702, and module 705 may be coupled to the machine's control system, and can be organically integrated with the machine's controller through parameter adjustment module 705 for dynamic on-line calibration of the machine. In particular, parameter adjustment module 705 provides an interface to machining center 306 allowing transmission of calibration information for the machine based on positioning performance of the machine tool as measured by the ballbar sensor. This calibration information is then used by machining center 306. Parameter adjustment module 705 may be implemented as software designed to transmit calibration parameters to a particular machining center 306. according to that machining center's external control capabilities. Preferably, as industry standard interface architectures are developed for control and monitoring of machine tools from various manufacturers, parameter adjustment module 705 will be adapted to provide inputs to an Open Architecture Control (OAC). The ballbar analysis software preferably provides data from each ballbar test to a statistical process control program such as ballbar analysis software 702 running in conputer 206, which monitors accuracy, variability, and trends in accuracy of the tested machine using conventional industrial statistical process control techniques. As shown in Figure 7, the statistical process control software can also operate in a centrally located shop floor computer 703, connected to receive data from the ballbar system, for process monitoring of a plurality of machines. If desired, the ballbar analysis software can similarly reside in a remotely located computer which serves one or more CNC machines. Those skilled in the art will appreciate that the concepts presented herein could also be applied to other types of measuring and calibration tools which can be usefully operated in an automatic mode on a machine tool.

Claims: I claim: 1. An automatic monitoring system for a numerically controlled machine tool of a type having a tool storage and an automatic tool changer which selectively transfers a plurality of tools with standard tool heads compatible with that machine between the tool storage and a tool actuator of the machine, comprising: base unit means for establishing a fixed reference position; sensing means associated with the base unit means for producing an output indicating the relative position ofthe machine actuator and the fixed reference position; actuator connection means attached to one of said standard tool heads for automatic installation on the actuator of the machine and operable attachment to the sensing means; computing means for receiving the output of the sensing means and recording motion of the machine actuator relative to the fixed reference position; and control means for selectively automatically activating the automatic tool changer to install said actuator connection means on the machine actuator, moving said actuator connection means so that said sensing means is operably located relative to said actuator connection means and said base unit means, actuating said computing means to record a preprogrammed motion of the machine actuator, and then activating said automatic tool changer to return said actuator connection means to the tool storage. 2. The system of claim 1 wherein said sensing unit means is stored in association with said base unit means and said control means moves said actuator connection means to engage said sensing unit means. 3. The system of claim 1 wherein said sensing unit means is a telescoping ballbar sensor and said control means includes movement pattern control means for moving the machine tool actuator in a predetermined controlled-motion pattern appropriate for a ballbar test. 4. The system of claim 3 wherein the base unit means has a fixed sphere, the ballbar sensor has a sphere at a first end thereof and a socket mating with the sphere of the base unit means at a second end thereof, and the actuator connection means has a socket mating with the sphere of the ballbar sensor. 5. The system of claim 1 wherein said base unit means is fixed in a predetermined location on a table of the machine tool. 6. The system of claim 1 wherein said base unit means includes pickup means for facilitating automatic movement of said base unit means by said machine tool actuator, and wherein said control means actuates the machine tool to selectively place said base unit means in a predetermined location on a table ofthe machine tool. 7. The system of claim 1 wherein said control means includes automated test activation means for automatically initiating a test sequence at predetermined times, including at least one of: during loading and unloading of the machine, between production runs, at downtimes, and at periodic predetermined time intervals. 8. The system of claim 1 further comprising analysis means associated with said computing means for statistically analyzing the sensing means output to monitor accuracy of machine tool positioning control. 9. The system of claim 1 further comprising dynamic calibration means connected to the computing means for automatically recalibrating a positioning control system of the machine tool actuator in response to measured differences between programmed motion of the machine actuator and motion of the machine actuator recorded by the computing means. 10. The system of claim 1 further including wireless connection means for transmitting data between the sensing means and the computing means. 11. An on-machine ballbar monitoring system for a numerically controlled machine tool of a type having a tool storage and an automatic tool changer which selectively transfers a plurality of tools with standard tool heads compatible with that machine between the tool storage and a tool actuator of the machine, comprising: base unit means for establishing a fixed reference position; sensing means for producing an output indicating the relative position ofthe machine actuator and the fixed reference position, said sensing means including a telescopic ballbar sensor adapted to connect with the base unit means; actuator connection means attached to one of said standard tool heads for automatic installation on the actuator of the machine and operable attachment to the telescopic ballbar sensor; computing means for receiving the output of the sensing means and recording motion of the machine actuator relative to the fixed reference position; and control means connected to the machine tool and the computing means for selectively automatically activating the automatic tool changer to install said actuator connection means on the machine actuator, moving the machine tool actuator so that said telescopic ballbar sensor extends between said actuator connection means and said base unit means, actuating the machine tool and said computing means to record a preprogrammed motion pattern of the machine actuator, and then activating said automatic tool changer to return said actuator connection means to the tool storage. 12. The system of claim 1 1 wherein said telescoping ballbar sensor is stored in association with said base unit means and said control means moves said actuator connection means to engage the ballbar sensor. 13. The system of claim 12 wherein the base unit means has a fixed sphere, the ballbar sensor has a sphere at a first end thereof and a socket mating with the sphere of the base unit means at a second end thereof, and the actuator connection means has a socket mating with the sphere of the ballbar sensor. 14. The system of claim 11 wherein said base unit means is fixed in a predetermined location on a table of the machine tool. 15. The system of claim 11 wherein said base unit means includes pickup means for facilitating automatic movement of said base unit means by said machine tool actuator, and wherein said control means actuates the machine tool to selectively place said base unit means in a predetermined location on a table of the machine tool. 16. The system of claim 1 1 wherein said control means includes automated test activation means for automatically initiating a test sequence at predetermined times, including at least one of: during loading and unloading of the machine, between production runs, at downtimes, and at periodic predetermined time intervals. 17. The system of claim 1 1 further comprising analysis means associated - 14 - with said computing means for statistically analyzing the sensing means output to monitor accuracy of machine tool positioning control. 18. The system of claim 1 1 further comprising dynamic calibration means connected to the computing means for automatically recalibrating a positioning control system of the machine tool actuator in response to measured differences between programmed motion of the machine actuator and motion of the machine actuator recorded by the computing means. 19. The system of claim 11 further including wireless connection means for transmitting data between the ballbar sensor and the computing means. 20. A method for automatically monitoring a numerically controlled machine tool of a type having a tool storage and an automatic tool changer which selectively transfers a plurality of tools with standard tool heads compatible with that machine between the tool storage and a tool actuator of the machine, comprising the steps of: (a) placing on a table of the machine tool a base unit means for establishing a fixed reference position; (b) providing a sensing means associated with the base unit means for producing an output indicating the relative position of the machine actuator and the fixed reference position; (c) installing in the tool changer an actuator connection means for operable attachment to the sensing means, the actuator connection means having one of said standard tool heads; (d) selectively activating the automatic tool changer to install said actuator connection means on the machine actuator; (e) moving said actuator connection means so that said sensing means is operably located relative to said actuator connection means and said base unit means; (f) actuating a data processing device during a preprogrammed motion of the machine actuator to receive the output of the sensing means and record motion of the machine actuator relative to the fixed reference position; and (g) activating said automatic tool changer to return said actuator connection means to the tool storage following said preprogrammed motion of the machine actuator. 21. The method of claim 20 wherein said sensing unit means is stored in association with said base unit means and said control means moves said actuator connection means to engage said sensing unit means. 22. The method of claim 20 wherein said sensing unit means is a telescoping ballbar sensor and said preprogrammed motion ofthe machine moves the machine in a pattern appropriate for a ballbar test. 23. The method of claim 22 wherein the base unit means has a fixed sphere, the ballbar sensor has a sphere at a first end thereof and a socket mating with the sphere of the base unit means at a second end thereof, and the actuator connection means has a socket mating with the sphere of the ballbar sensor. 24. The method of claim 20 wherein said base unit means is fixed in a predetermined location on a table of the machine tool. 25. The method of claim 20 wherein said base unit means includes pickup means for facilitating automatic movement of said base unit means by said machine tool actuator, and including the further step of actuating the machine tool to selectively place said base unit means in a predetermined location on a table of the machine tool before performing step (e). 26. The method of claim 20 including the further step of automatically initiating a test sequence including steps (d) through (g) at predetermined times. 27. The method of claim 26 wherein said predetermined times include at least one of: during loading and unloading of the machine, between production runs, at downtimes, and at periodic predetermined time intervals. 28. The method of claim 20 comprising the further step of statistically analyzing the sensing means output to monitor accuracy of machine tool positioning control. 29. The method of claim 20 comprising the further step of automatically recalibrating a positioning control system of the machine tool actuator in response to measured differences between programmed motion of the machine actuator and said recorded motion of the machine actuator. 30. The method of claim 20 wherein data is transmitted wirelessly between the sensing means and the data processing device. 31. An automatic calibration system for a numerically controlled machine tool of a type having a tool storage and an automatic tool changer which selectively transfers a plurality of tools with standard tool heads compatible with that machine between the tool storage and a tool actuator of the machine, comprising: base unit means for establishing a fixed reference position; sensing means associated with the base unit means for producing an output indicating the relative position of the machine actuator and the fixed reference position; actuator connection means attached to one of said standard tool heads for automatic installation on the actuator of the machine and operable attachment to the sensing means; computing means for receiving the output of the sensing means and recording motion of the machine actuator relative to the fixed reference position; control means for selectively automatically activating the automatic tool changer to install said actuator connection means on the machine actuator, moving said actuator connection means so that said sensing means is operably located relative to said actuator connection means and said base unit means, actuating said computing means to record a preprogrammed motion of the machine actuator, and then activating said automatic tool changer to return said actuator connection means to the tool storage; and dynamic calibration means connected to the computing means for automatically recalibrating a positioning control system of the machine tool actuator in response to measured differences between programmed motion of the machine actuator and motion of the machine actuator recorded by the computing means. 32. The system of claim 31 wherein said sensing unit means is a telescoping ballbar sensor and said control means includes movement pattern control means for moving the machine tool actuator in a predetermined controlled-motion pattern appropriate for a ballbar test. 33. The system of claim 32 wherein the base unit means has a fixed sphere, the ballbar sensor has a sphere at a first end thereof and a socket mating with the sphere of the base unit means at a second end thereof, and the actuator connection means has a socket mating with the sphere of the ballbar sensor. 34. The system of claim 32 wherein said base unit means is fixed in a predetermined location on a table of the machine tool. 35. The system of claim 32 wherein said base unit means includes pickup means for facilitating automatic movement of said base unit means by said machine tool actuator, and wherein said control means actuates the machine tool to selectively place said base unit means in a predetermined location on a table of the machine tool. 36. The system of claim 32 wherein said control means includes automated test activation means for automatically initiating a test sequence at predetermined times, including at least one of: during loading and unloading of the machine, between production runs, at downtimes, and at periodic predetermined time intervals. 37. The system of claim 32 further comprising analysis means associated with said computing means for statistically analyzing the sensing means output to monitor accuracy of machine tool positioning control. 38. A method for automatically calibrating a numerically controlled machine tool of a type having a tool storage and an automatic tool changer which selectively transfers a plurality of tools with standard tool heads compatible with that machine between the tool storage and a tool actuator of the machine, comprising the steps of: (a) placing on a table of the machine tool a base unit means for establishing a fixed reference position; (b) providing a sensing means associated with the base unit means for producing an output indicating the relative position of the machine actuator and the fixed reference position; (c) installing in the tool changer an actuator connection means for operable attachment to the sensing means, the actuator connection means having one of said standard tool heads; (d) selectively activating the automatic tool changer to install said actuator connection means on the machine actuator; (e) moving said actuator connection means so that said sensing means is operably located relative to said actuator connection means and said base unit means; (f) actuating a data processing device during a preprogrammed motion of the machine actuator to receive the output of the sensing means and record motion of the machine actuator relative to the fixed reference position; (g) activating said automatic tool changer to return said actuator connection means to the tool storage following said preprogrammed motion of the machine actuator; and (h) automatically recalibrating a positioning control system of the machine tool actuator in response to measured differences between programmed motion of the machine actuator and said recorded motion of the machine actuator. 39. The method of claim 38 wherein said sensing unit means is a telescoping ballbar sensor and said preprogrammed motion of the machine moves the machine in a pattern appropriate for a ballbar test. 40. The method of claim 39 wherein the base unit means has a fixed sphere, the ballbar sensor has a sphere at a first end thereof and a socket mating with the sphere of the base unit means at a second end thereof, and the actuator connection means has a socket mating with the sphere of the ballbar sensor. 41. The method of claim 38 wherein said base unit means is fixed in a predetermined location on a table of the machine tool. 42. The method of claim 38 wherein said base unit means includes pickup means for facilitating automatic movement of said base unit means by said machine tool actuator, and including the further step of actuating the machine tool to selectively place said base unit means in a predetermined location on a table of the machine tool before performing step (e). 43. The method of claim 38 including the further step of automatically initiating a test sequence including at least steps (d) through (g) at predetermined times. 44. The method of claim 43 wherein said predetermined times include at least one of: during loading and unloading of the machine, between production runs, at downtimes, and at periodic predetermined time intervals. 45. The method of claim 38 comprising the further step of statistically analyzing the sensing means output to monitor accuracy of machine tool positioning control.

Inventors: LAU KAM C, LAU, KAM, C.
Applicants: LAU KAM C, LAU, KAM, C.
Application year: 1996
Main classification: G01B5
IPC codes: B23Q15, B23Q17, B25J9, G01B5, G01B21, G05B19