Patent Application
20090211338
The invention is in the field of measuring devices. Some aspects of the invention are in the field of computer numerically controlled machines and related methods.
Computer numerically controlled machines are widely used to cut forms of metal and other materials in operations such as milling, drilling, grinding, broaching, turning, and the like (such operations being termed “cutting operations” generally). In most cases, and in particular when cutting high-precision forms such as gears and engine parts, there is a need to measure the item being cut and/or the tool used in the machine. Such measuring may be conducted either during or after the cutting operation, and may be performed inside or outside of the machine. Measuring generally is conducted to determine whether the size of the form or tool is within a desired degree of tolerance or to determine proper adjustments to the cutting operation. In particular, measurement during a cutting operation is desirable because it allows corrections to be made more rapidly.
Generally, measurements may be taken either within the CNC machine or externally after removal of the item to be measured from the machine. External measurement, while often useful, is disfavored for a number of reasons. External measurements can make it difficult to conduct extended unattended operations, particularly if tool wear is high. In offline gauging, the part is measured outside the machine after machining is complete. Typically, this is carried out in a separate temperature-controlled room. If a machine is kept running during the measuring step, and if the measured part should prove to be out of tolerance, the machine will have kept producing out-of-tolerance parts. It is common, therefore, for machining to cease until the part measurement is complete, thus reducing productivity of the operation. Additionally, if the workpiece is out of tolerance, an adjustment in the tool offset or insert position is required. Depending on the measurement taken in the measuring step, an operator may need to calculate the necessary adjustment and adjust the machine. This can lead to operator error and additional production of out-of-tolerance parts.
In many cases, multiple machines are employed to produce the same part. In this case, operators need to keep track of which parts came from which machine, thus possibly leading to confusion.
The prior art has provided automotive measuring offline gauging systems which can provide automatic feedback. Such systems are typically expensive and complicated.
Conversely, many known in-machine measurement systems are unsatisfactory. There is often a trade off between robustness of the device and accuracy of measurement. For instance, touch probes, which are suitable for some purposes, in many cases are not sufficiently accurate for high-precision work. This is in part because touch probes depend on the accuracy of the machine. Additionally, touch probes have longer measurement cycles than other measurement devices, and accordingly they are less productive. Other devices, including air gages and linear variable differential transformers (LVDTs), in some cases are not sufficiently robust to withstand the harsh environment within a CNC machine. They are subject to contamination due to swarf, and may lead to incorrect measurements.
One of the inventors of the present application earlier has devised a measuring device (certain embodiments of which are disclosed in U.S. Pat. No. 6,901,797) that attempts to address the foregoing. The device disclosed in the '797 patent employs an incompressible fluid, typically a liquid, to achieve an in-machine measurement using known pneumatic measuring techniques.
The present invention seeks, in certain embodiments, to provide a measuring device that differs from the measuring device disclosed in the '797 patent. The invention seeks in some embodiments to provide a device that may be used in connection with a computer numerically controlled machine.
It has not been found that a CNC machine may be supplied with a measuring device that includes a nozzle and a source of incompressible fluid. The fluid may be delivered to the nozzle during the course of taking a measurement reading. By measuring the pressure of the fluid as the nozzle is moved into proximity with the item to be measured, a measurement parameter may be determined. The measurement parameter may be, for instance, a dimension of the item being measured, the center position of a bore, the centerline of an item, or any other suitable measurement parameter. The fluid may be delivered at a constant volumetric flow rate during the course of taking a measurement reading. The measurement parameter so measured may be used in many ways; for instance, in adjusting total offsets, re-cutting a workpiece, determining whether a workpiece is within specification, or causing another program to run.
Thus, in one embodiment, the invention provides an apparatus that includes a first holder and at least one tool holder, the first holder and tool holder being movable with respect to one another, and a computer control system that is operatively connected to the first holder and to the tool holder. A measuring device that includes a nozzle having at least one orifice is also provided, the nozzle being disposable in the tool holder. The measuring device includes a source of a substantially incompressible fluid, the source being in fluid communication with, or fluidically communicable with, the nozzle. The measuring device is further equipped with a fluid pumping device that is configured to supply at least a portion of the fluid at a constant volumetric flow rate to the nozzle during a measuring operation, and a device for measuring the pressure of the fluid and for communicating electronic information relating to the pressure to a computing device. The computing device, which may be the heretofore referenced machine computer control system or a separate computing device, is configured to determine a measurement parameter for an item that is disposed in the first holder. The computing device may be, for instance, a microcontroller or other controller. The item to be measured may be, for instance, a workpiece, a tool, or a calibration device as hereinafter described.
The invention is not limited to a CNC machine. In accordance with one embodiment, a measuring device is provided. The measure device includes a nozzle and a source of incompressible fluid that may be delivered at a constant volumetric flow rate to the nozzle during the course of taking a measurement reading.
In another embodiment, an apparatus includes at least first, second, and third holders, the first holder holding a workpiece, the second holder being configured to hold a tool, and the third holder being configured to hold the nozzle of a measurement device as discussed hereinabove. Material is removed from the workpiece simultaneously as the workpiece is measured. In this embodiment, fluid may, but need not be delivered at a constant volumetric flow rate while measuring the workpiece. Measurement simultaneously with removal of material can provide a number of advantages. For instance, the removal of the material may be terminated if a predetermined error limit has been surpassed (the error limit intended to indicate a problem, such as breakage of the tool or an out-of-specification workpiece). In other embodiments, removal of material from workpiece, or from a portion of the workpiece, is caused to cease when the measuring device determines that sufficient material has been removed from the workpiece. An apparatus that contains computer-executable code for accomplishing the foregoing may be provided.
Other methods and apparatus as provided include an integrated cutting tool and nozzle. For instance, a cutting tool may comprise a boring bar. A method and an apparatus using a measuring tool and an integrated tool and nozzle may provide a number of advantages. In some embodiments, cutting and measuring are separate steps performed sequentially; in other embodiments, measurement is simultaneous with removal of material from the tool.
In another embodiment, the invention provides a method. Using an apparatus as heretofore described, a measurement reading is taken and a measurement parameter determined. A measuring operation may comprise taking a single reading or taking multiple readings. When multiple readings are taken in a single measuring operation, the computer may employ an algorithm to determine the measurement parameter based on the multiple readings.
Further features of certain embodiments of the invention are described hereinbelow. The scope of the invention should not be deemed limited by the above summary or the following description, but rather is defined by the appended claims as construed in accordance with applicable law.
Any suitable apparatus may be employed in conjunction with the methods of invention. In some embodiments, the methods are performed using a computer numerically controlled machine, illustrated generally in
In general, with reference to the NT-series machine illustrated in
As shown in
The computer numerically controlled machine 100 is provided with a computer control system for controlling the various instrumentalities within the computer numerically controlled machine. In the illustrated embodiment, the machine is provided with two interlinked computer systems, a first computer system comprising a user interface system (shown generally at 114 in
As further illustrated in
The spindle 144 is mounted on a carriage assembly 120 that allows for translational movement along the X- and Z-axes, and on a ram 132 that allows the spindle 144 to be moved in the Y-axis. The ram 132 is equipped with a motor to allow rotation of the spindle in the B-axis, as set forth in more detail hereinbelow. As illustrated, the carriage assembly has a first carriage 124 that rides along two threaded vertical rails (one rail shown at 126) to cause the first carriage 124 and spindle 144 to translate in the X-axis. The carriage assembly also includes a second carriage 128 that rides along two horizontally disposed threaded rails (one shown in
The spindle 144 holds the cutting tool 102 by way of a spindle connection and a tool holder 106. The spindle connection 145 (shown in
The first chuck 110 is provided with jaws 136 and is disposed in a stock 150 that is stationary with respect to the base 111 of the computer numerically controlled machine 110. The second chuck 112 is also provided with jaws 137, but the second chuck 112 is movable with respect to the base 111 of the computer numerically controlled machine 100. More specifically, the machine 100 is provided with threaded rails 138 and motors 139 for causing translation in the Z-direction of the second stock 152 via a ball screw mechanism as heretofore described. To assist in swarf removal, the stock 152 is provided with a sloped distal surface 174 and a side frame 176 with Z-sloped surfaces 177, 178. Hydraulic controls and associated indicators for the chucks 110, 112 may be provided, such as the pressure gauges 182 and control knobs 184 shown in
The turret 108, which is best depicted in
It is thus seen that a wide range of versatile operations may be performed. With reference to tool 102 held in tool holder 106, such tool 102 may be brought to bear against a workpiece (not shown) held by one or both of chucks 110, 112. When it is necessary or desirable to change the tool 102, a replacement tool 102 may be retrieved from the tool magazine 142 by means of the tool changing device 143. With reference to
The components of the machine 100 are not limited to the heretofore described components. For instance, in some instances an additional turret may be provided. In other instances, additional chucks and/or spindles may be provided. Generally, the machine is provided with one or more mechanisms for introducing a cooling liquid into the chamber 116.
In the illustrated embodiment, the computer numerically controlled machine 100 is provided with numerous retainers. Chuck 110 in combination with jaws 136 forms a retainer, as does chuck 112 in combination with jaws 137. In many instances these retainers will also be used to hold a workpiece. For instance, the chucks and associated stocks will function in a lathe-like manner as the headstock and optional tailstock for a rotating workpiece. Spindle 144 and spindle connection 145 form another retainer. Similarly, the turret 108, when equipped with plural turret connectors 134, provides a plurality of retainers (shown in
The computer numerically controlled machine 100 may use any of a number of different types of cutting tools known in the art or otherwise found to be suitable. For instance, the cutting tool 102 may be a milling tool, a drilling tool, a grinding tool, a blade tool, a broaching tool, a turning tool, or any other type of cutting tool deemed appropriate in connection with a computer numerically controlled machine 100. As discussed above, the computer numerically controlled machine 100 may be provided with more than one type of cutting tool, and via the mechanisms of the tool changing device 143 and magazine 142, the spindle 144 may be caused to exchange one tool for another. Similarly, the turret 108 may be provided with one or more cutting tools 102, and the operator may switch between cutting tools 102 by causing rotation of the turret 108 to bring a new turret connector 134 into the appropriate position.
Other features of a computer numerically controlled machine include, for instance, an air blower for clearance and removal of chips, various cameras, tool calibrating devices, probes, probe receivers, and lighting features. The computer numerically controlled machine illustrated in
The computer numerically controlled machine in accordance with some embodiments of the invention is provided with a measuring device. The exemplary device 200 illustrated in
Generally, the measuring device may be incorporated into a computer numerically controlled machine in a suitable matter. It is further contemplated that the measuring device in some embodiments of the invention is a device that is not incorporated with a computer numerically controlled machine. When incorporated with a computer numerically controlled machine, the nozzle may be employed on any suitable holder or retainer in the machine, such as on a turret connector 134, the machine spindle 144, or one of the chucks 110, 112. It is contemplated that the cutting tool may be disposed on another holder in the machine, and it is also completed that a workpiece may be disposed in yet another holder of the machine. Enumerating the holder that contains a workpiece as a first holder, the holder that contains the tool as a second holder, and the holder that retains the nozzle as a third holder, it is contemplated that the first holder should be moveable relative to the second holder and that the third holder likewise should be movable with respect to the second holder. It is contemplated that in some embodiments the first and third holder will be movable relative to one another. In other embodiments, it is contemplated that the first and third holder are stationary and not movable with respect to one another (e.g., if the tool and nozzle are carried together in a carriage (not shown)). Additionally, as discussed hereafter, it is contemplated that the tool and nozzle may be integrated, and, in such embodiments, the tool and nozzle may be carried in the same holder. In such embodiments, the holder that contains the tool and the nozzle should be movable relative to the holder that contains the workpiece.
The transducer 206 may be any device now known in the art or otherwise found to be suitable for sending electrical signals relating to pressure. The transducer 206 may measure pressure in the line 203 or in an afterchamber (not shown) or in any other location suitable to allow for a pressure-based measurement reading to be taken. The communication path 208 between the transducer 206 and the computing device 210 is shown in
The fluid source 201 is equipped with a pump that is configured to provide a constant volumetric flow rate to the nozzle during the course of taking a measurement reading. In accordance with some embodiments of the invention, the pump may be a pump that is configured to permit adjustment of the rate of revolution and thus the volume of fluid conveyed for revolution. In some embodiments, the pump may comprise a swash plate pump that allows for the adjustment of the stroke and plate angle to thereby provide volume adjustment capability at constant speed of rotation. In such embodiments, the rotational speed of the pump may be constant or may be variable. As hereinafter discussed, the swash pump also may be configured to permit adjustments to the volumetric flow rate over the course of multiple readings. In some embodiments, the volumetric flow rate may be varied when measuring different features of an item.
It is contemplated, in some embodiments, that the flow rate may be estimated based on an estimated dimension of the item to be measured. Generally, for a larger item with a larger estimated measurement parameter, it will be desired to employ a larger volumetric flow rate than for a smaller item. It is contemplated that the flow rate may be varied either manually or automatically using the control systems of the machine. In some embodiments, the flow rate is adjusted by adjusting the rate of revolution of a pump. In other embodiments, where a swash pump is employed, the volumetric flow rate is adjusted by adjusting the swash mechanism to vary the displacement per revolution of the pump.
The nozzle 202 may be included within the computer-numerically controlled machine at any suitable location. For instance, in the machine illustrated in
The nozzle 202 and associated plug may take any appropriate form. In some embodiments, it is contemplated that the nozzle may rotate during the course of taking of measurement reading. In other embodiments, it is contemplated that the nozzle 202 does not rotate during the course of taking a measurement reading, i.e., that the nozzle 202 is a non-rotational nozzle. The exact configuration of the nozzle 202 and the rotation or non-rotation of the nozzle 202 during the course of taking a measurement reading will, in a particular situation, be selected in a manner consistent with the requirements at hand.
In operation, when it is desired to take a measurement reading, the pump is operated and fluid is conveyed to the nozzle 202 at a base pressure. Any suitable base pressure may be employed, but it has been found useful to employ a base pressure of about 300 psi or greater, in some embodiments 400 psi or greater, and in some embodiments 500 psi or greater. Generally, it is desired to conduct measurement at a pressure that is as high as possible given the limits of the machine, with appropriate safety tolerances. If, for instance, the maximum safe operating pressure is 1000 psi and a pressure increase of 500 psi is expected, the operator may select a base pressure of 300 or 400 psi to come close to the maximum safe operating pressure without exceeding it. Conveyance of a liquid at these pressures is believed to assist in removing swarf from the measurement site on the item being measured and in permitting the nozzle 202 to operate at a distance from the item being measured (in
The distance between the orifice and the item being measured may be any value suitable to allow for a pressure-based measurement reading. In some embodiments, it has been found that the distance between the orifice and the item being measured may be larger than that employed in air gauging. Typical prior air gauge plugs require a small gap (on the order of two-thousandths of an inch). In connection with measurement of finely featured items, such as gears and threaded surfaces, prior art air gauge plugs generally cannot be employed, or can be employed only with difficulty. In contrast, in some embodiments of the present invention, the gap between the orifice and the item being measured may be larger. In some embodiments, it is possible to employ a gap in the order of five thousandths of an inch. This allows for use of a gage that meshes with a threaded item or with a gear. Generally, it is contemplated that the average dimension of the thread or gear may be measured, allowing the operator to accept or reject the item as appropriate.
During the course of a measuring operation, multiple measurement readings may be taken. In such event, the computer may be configured to determine a measurement parameter algorithmically based on the multiple readings. The algorithm may be applied to the data set generated by the pressure transducer 206 before determining a measurement parameter, or may be applied to the data set of measurement parameters determined after calculation of plural measurement parameters based on plural readings. For instance, the algorithm may be as simple as determining the mean average of the measurement parameters obtained over the course of multiple readings. In another algorithm, plural measurement readings are taken, and the high and low measurement readings (or the high and low data readings from the pressure transducer) are discarded, and the mean average of the remaining values is determined. Numerous other, more complex algorithms may be employed.
When a swash pump is employed, the pump may be operated in various ways consistent with the foregoing. For instance, in taking plural readings, a constant volumetric flow rate may be applied in each case, and the settings of the swash pump (volume per revolution), may be kept constant. Alternatively, during the course of a measuring operation, plural readings may be taken using a constant volumetric flow rate but by varying the swash pump parameters. Again, when measuring different features of an item, different volumetric flow rates may be employed. In some embodiments, it is contemplated that the constant volumetric flow rate may be varied from one reading to another over the course of plural readings taken during a single measuring operation. In any case, the volumetric flow rate should be kept constant during the course of a measurement reading; the term “constant” signifying constant within the limits of the machine or within a surrounding predetermined range of tolerance.
The measuring device may be provided with a single nozzle or with plural nozzles, and in either case, may be provided with nozzles of general application or nozzles designed specifically for measurement of a form of predetermined configuration. The nozzle 211 illustrated in
The exact relationship of a particular pressure reading to a particular dimension cannot be stated as a general matter, because this relationship will depend on a number of factors, including the pressure employed in the line 203, the configuration of the pressure transducer 206, and other factors. Generally, the measuring device 200 should be calibrated. To assist in calibrating the measuring device 200, and, after initial calibration, to assist in periodic calibrating adjustment of the device 200 one or more calibration devices may be provided. As shown in
As shown in
The measuring device may be used to provide feedback to the operator (or to the computer control system) of the CNC machine. For instance, after providing a workpiece and removing material from the workpiece, a measuring operation may be conducted. If sufficient material has been removed from the workpiece and a workpiece has a dimension within a suitable range of tolerance, the workpiece may be removed from the machine and, if desired, a new workpiece introduced. On the other hand, if sufficient material has not been removed from the workpiece, the measuring device may be disengaged and more material removed from the workpiece as appropriate.
As heretofore discussed, in some embodiments, a tool may be integrated with a nozzle, as shown, for instance, in
An alternative boring bar 257 shown in
As shown in
In this embodiment, it is contemplated that there may be a period of delay between the time the desired measurement is reached and the disengagement of the tool and the workpiece. This delay, which may otherwise cause a workpiece to fall out of specification in high-precision applications, may be addressed by appropriate compensation in the measurement parameter. It is noted that the foregoing allows for very high precision in operations, irrespective of wear of the tool (for instance, wear of the grinding wheel 265). Even if the rate of wear of the tool is not known with certainty, a high-precision cutting operation is enabled.
In either embodiment, simultaneous measurement and removal of material from the workpiece may be employed to cause termination of the removal of material if a predetermined error limit has been reached. For instance, if the tool breaks during a cutting operation where a tool is traversing the workpiece, the measuring device will determine that there is a large and abrupt change in the measured dimension. The machine can be programmed to cause to tool to disengage from the workpiece in such instance. Also, particularly in a high-volume application, one or more workpieces may be out of specification, and the measuring device may be used to detect this and to cause a termination of the operation for a machine operator to take appropriate corrective action.
In another mode of operation, the measuring device is operated in a “skip signal” mode of operation. In this embodiment, the machine motion is terminated when a predetermined pressure has been reached, or alternatively another suitable action is taken. Pressure may be monitored continuously or may be sampled intermittently. This mode of operation is useful, for instance, in preventing contact with the nozzle with the form being measured. For instance, using a single orifice plug and a part where the user is not certain of the dimension to be measured, the skip signal mode of operation may be employed. The user may position the orifice of one limit of the estimated range of the part dimension, then advance the nozzle towards the other limit of the estimated range. In a computer numerically controlled machine, this may be accomplished via a suitable machine program. The machine or controller program would continuously monitor or periodically sample pressure in the line. As the gap between the orifice and the part reduces, the pressure in the line will increase. The machine movement then can be stopped by issuing a skip signal when the pressure in the line receives a predetermined limit.
Generally, while the measuring apparatus has been shown in connection with a CNC machine that employs a turret, spindle, and plural chucks, the measuring device may be used in simpler CNC machines, or, more conversely in more complex such machines.
In practice, the measuring device has proven to allow for excellent accuracy and repeatability. In one embodiment, a bore having an interior diameter of roughly 3.5 inches was measured in a measuring operation. Thirty measurement readings were taken and were found to be consistent over a measurement range of 77 millionths of an inch (approximately 2 microns). Operation at a constant volumetric flow rate is believed to be advantageous over system described in the prior '797 patent and to be simpler in operation over the prior system.
Thus, it is seen that a measuring device may be provided.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference. The description of certain embodiments as “preferred” embodiments, and other recitation of embodiments, features, or ranges as being preferred, is not deemed to be limiting, and the invention is deemed to encompass embodiments that are presently deemed to be less preferred. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended to illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Any statement herein as to the nature or benefits of the invention or of the preferred embodiments is not intended to be limiting, and the appended claims should not be deemed to be limited by such statements. More generally, no language in the specification should be construed as indicating any non-claimed element as being essential to the practice of the invention. This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
The description herein of any reference or patent, even if identified as “prior,” is not intended to constitute a concession that such reference or patent is available as prior art against the present invention.
