Patent Description:
Grinding machines can be used to machine or grind elongated workpieces. The elongated workpiece can be held at a head and a tail and rotated so that one or more grinding wheels contact an outer surface of the workpiece and shape that surface by removing material. Elongated workpieces may be crankshafts that are used in internal combustion engines (ICEs) or pumps. The journal surfaces and crankpin surfaces of a crankshaft are carefully ground so that the surfaces have very precise sizes and shapes. A grinding machine can locate a surface of an elongated workpiece by physically contacting the surface with a dedicated probe and, when contact is made, the machine can determine where the surface is located. A grinding machine according to the preamble of claims <NUM> and <NUM> is disclosed by <CIT>. However, it is possible to increase the precision with which the surface is located and/or measured.

In one implementation, a grinding machine including one or more grinding wheels has a workpiece holder that releasably holds a crankshaft and is configured to rotate the crankshaft about a longitudinal axis; a spindle assembly, that is moveable in at least two directions, including a spindle shaft and a grinding wheel attached to the spindle shaft; and an acoustic emission sensor coupled to the grinding machine, such that the grinding machine is configured to monitor an output signal from the acoustic emission sensor, move the grinding wheel into contact with the crankshaft at a first angular position, detect contact between the grinding wheel and the crankshaft based on the output signal, determine a position of the grinding wheel based on the detected contact between the grinding wheel and the crankshaft, move the grinding wheel away from the crankshaft, rotate the crankshaft a defined angular amount, move the grinding wheel into contact with the crankshaft at a second angular position, determine a position of the grinding wheel based on the detected contact between the grinding wheel and the crankshaft, and determine a position of a crankshaft surface.

In another implementation, a method of determining a grinding wheel position and a position of a crankshaft surface of a crankshaft includes determining an angular position of a crankshaft held by a workpiece holder; moving a grinding wheel coupled with a spindle shaft toward the crankshaft; monitoring an acoustic emission sensor as the grinding wheel moves toward the crankshaft before grinding begins; detecting when the grinding wheel contacts the crankshaft based on output from the acoustic emission sensor; moving the grinding wheel away from the crankshaft; rotating the workpiece a defined angular amount to a second angular position; moving the grinding wheel toward the crankshaft at the second angular position; monitoring the acoustic emission sensor as the grinding wheel moves toward the crankshaft at the second angular position before grinding begins; detecting when the grinding wheel contacts the crankshaft at the second angular position based on output from the acoustic emission sensor; determining a position of the grinding wheel, determining a position of the crankshaft surface based on the preceding steps.

In another implementation, a grinding machine includes one or more grinding wheels and a workpiece holder that releasably holds a crankshaft and is configured to rotate the crankshaft about a longitudinal axis; a spindle assembly, that is moveable in at least two directions, including a spindle shaft and a grinding wheel attached to the spindle shaft; and a microprocessor configured to measure electrical power consumed by a spindle motor, wherein the grinding machine moves the grinding wheel into contact with the crankshaft at a first angular position, detects contact between the grinding wheel and the crankshaft based on a change in the electrical power consumed by the spindle motor, determines a position of the grinding wheel based on the detected contact between the grinding wheel and the crankshaft, moves the grinding wheel away from the crankshaft, rotates the crankshaft a defined angular amount, moves the grinding wheel into contact with the crankshaft at a second angular position, determines a position of the grinding wheel based on the detected contact between the grinding wheel and the crankshaft, and determines a position of a crankshaft surface.

A grinding machine uses acoustic detection to determine the location of a workpiece relative to a grinding wheel. In particular, an orbital grinding machine can include an acoustic emission sensor that acoustically detects when a grinding wheel is moved into contact with a workpiece surface, such as a crankpin or a journal bearing of a crankshaft before grinding begins. Dimensional tolerances of the workpiece surface can be reduced by acoustically detecting the location of the crankpin and/or journal bearing surfaces in the plane of operation, either alone or in combination with a physical probe. Before grinding begins, a grinding wheel can be moved into close proximity to the surface of the workpiece the grinding wheel will cut. The workpiece surface could be journal bearing surfaces or crankpins of a crankshaft. An acoustic emission sensor, such as a microphone, can be included with the grinding wheel, possibly at the wheel center or on a spindle assembly carrying the grinding wheel, and the grinding wheel can be moved toward the workpiece until the grinding wheel contacts the surface of the workpiece. The grinding machine can determine the position of the grinding wheel surface in space with tremendous precision. The acoustic emission sensor can detect the precise position of the spindle shaft carrying the grinding wheel when the grinding wheel contacts the surface of the workpiece by detecting the sound produced when contact occurs. A computer processor can monitor the point where the grinding wheel contacts the surface of the workpiece.

In contrast, past grinding machines solely used a physical probe attached to the end of a carriage to locate the crankpins or journal bearings of a crankshaft in space. While the probes are highly accurate, a number of variables involved with grinding workpieces can introduce additional error into the probe measurement. For example, larger crankshafts (i.e., ><NUM> meters) may tend to sag in the middle and also flex while machining or the grinding wheel can wear thereby reducing the distance between the wheel rotation axis about the spindle and the crankpins or journal bearing introducing error. Also, thermal variations can cause dimensional changes in the machine affecting overall accuracy of the probing process.

Presently, workpieces cut by grinding machines-such as crankshafts-can be hardened using one of a variety of different hardening techniques that leave a calculated thickness of hardening material. For example, crankshafts can be exposed to ammonia in a furnace that heats the crankshafts to nitride the surface. Currently, a crankshaft can receive ~ <NUM> of hardening material so that the errors in grinding will not unintentionally grind through the hardening material. But creating such a thickness of hardened material involves treating the crankshafts for a defined amount of time; thickness of hardening material on a crankshaft is positively correlated to time. It would be helpful to reduce the thickness of hardening material needed on the crankshaft thereby decreasing the amount of time spent applying hardening material. Determining the location of a journal bearing and/or a crankpin using an acoustic emission sensor before grinding can permit a reduced thickness of hardening material on the crankshaft. For example, it is possible to apply as little as <NUM> thick hardening material when using the acoustic emission sensor to detect journal bearing and/or crankpin location.

<FIG> depict a grinding machine <NUM> that includes at least one acoustic emission sensor <NUM> that detects acoustic emissions occurring when a grinding wheel <NUM> is moved into contact with a workpiece. In this embodiment, the grinding machine <NUM> is an orbital grinding machine designed to grind outer surfaces of crankshaft workpieces. More specifically, the orbital grinding machine can create journal surfaces and crankpin surfaces on a crankshaft <NUM>. In this implementation, the orbital grinding machine <NUM> can accommodate crankshafts small as <NUM> meters (m) and as long as <NUM>. One implementation of such a grinding machine <NUM> is a Fives Landis LT3e orbital crankshaft grinding machine. However, other embodiments using different types of workpieces or grinding machines can use acoustic emission sensors to determine the position of a grinding wheel with respect to the workpiece.

The orbital grinding machine <NUM> can include a workpiece holder <NUM> having a headstock <NUM> and a footstock <NUM>, a grinding wheel assembly <NUM> including a spindle assembly <NUM> coupled to the grinding wheel <NUM>, and a machine bed <NUM>. The machine bed <NUM> can be a relatively planar structure that rests on a floor and supports the elements of the grinding machine <NUM>. For example, the machine bed <NUM> can support the headstock <NUM> and footstock <NUM> on a surface of the machine bed <NUM> so that the crankshaft <NUM> is engaged with both the headstock <NUM> and footstock <NUM> and raised above the bed <NUM>. The machine bed <NUM> can be rectangular such that it is longer in length along a Z-axis than it is along a X-axis. One or more grinding wheel rails <NUM> can extend along the surface of the machine bed <NUM> along the Z-axis to facilitate movement of the grinding wheel assembly <NUM> along the Z-axis, such that the grinding wheel assembly <NUM> slides or rolls along the rails <NUM> in either direction to position the grinding wheel at a particular axial point along the X-axis. The grinding wheel assembly can be moved over the rails <NUM> along the Z-axis using a linear servo motor and optical scales can be used to identify the position of the grinding wheel <NUM> along the X-axis.

One or more workpiece holder rails <NUM> can be spaced apart from the grinding wheel rails <NUM>, positioned opposite the grinding wheel rails <NUM> on the machine bed <NUM>, extending along the Z-axis. The headstock <NUM> and the footstock <NUM> can slide or roll along the workpiece holder rails <NUM> to adjust for crankshafts having different axial lengths and engage a head of the crankshaft <NUM> and a tail of the crankshaft <NUM>, respectively, with a workpiece holder <NUM>, such as a chuck or collet, thereby holding the crankshaft <NUM> in a particular place. The workpiece holder <NUM> of the headstock <NUM> and the workpiece holder <NUM> of the footstock <NUM> can each include an electric motor that can, collectively in coordination, rotate the crankshaft <NUM> about its longitudinal axis (C) in a <NUM>-degree range of motion in either angular direction. Rotary encoders can be used at the headstock <NUM> and at the footstock <NUM> to determine the angular position of the crankshaft <NUM>. The headstock <NUM> and footstock <NUM> can each be individually moved along the Z-axis using servo motors and a rack drive.

The grinding wheel assembly <NUM> can include a base <NUM> that sits on the grinding wheel rails <NUM>. The spindle assembly <NUM> can be supported by the base <NUM> so that it is moveable along the z-axis over the grinding wheel rails <NUM> and includes a grinding wheel <NUM> coupled to the spindle assembly <NUM>, one or more infeed rails <NUM> in between the base <NUM> and the spindle assembly <NUM>, a linear servo motor, an optical scale, and an acoustic emission sensor <NUM>. The spindle assembly <NUM> can include a spindle drive motor <NUM> that turns a spindle shaft <NUM> ultimately rotating the grinding wheel <NUM> coupled to the spindle shaft <NUM>. The grinding wheel <NUM> can have a radial surface <NUM> that contacts the crankshaft <NUM> and faces outwardly from an axis of spindle shaft rotation (a). The spindle drive motor <NUM> can be concentric with the spindle shaft <NUM>, such that a rotor <NUM> of the spindle drive motor <NUM> is coupled with the spindle shaft <NUM> and a stator <NUM> is concentric with the rotor <NUM>. Forward bearing <NUM> and rearward bearing <NUM> can be positioned on opposite ends of the spindle shaft <NUM> providing support during operation. The bearings <NUM>, <NUM> can be implemented as hydrostatic bearings. A rotary encoder <NUM> can be attached to a distal end of the spindle shaft <NUM> for determining the angular position, velocity, or acceleration of the spindle shaft <NUM> and the grinding wheel <NUM>. The infeed rails <NUM> can extend along the X-axis and be positioned perpendicularly relative to the grinding wheel rails <NUM>.

The spindle assembly <NUM> can slide closer to and further away from the crankshaft <NUM> along the X-axis over the infeed rails <NUM>. The linear motor can move the grinding wheel assembly <NUM> over the infeed rails <NUM> along the X-axis using an electric motor turning a linear actuator, such as a ball screw, and an encoder that identifies the position of the grinding wheel assembly <NUM> along the X-axis. The grinding wheel assembly <NUM> can also include a touch probe <NUM> that extends from the grinding wheel assembly <NUM> to contact the crankshaft <NUM> at particular locations and determine the distance between the grinding wheel assembly <NUM> and the crankshaft <NUM> with a high degree of precision. The touch probe <NUM> can determine the location of a surface of a crankshaft, such as a crankpin or journal bearings, alone with a precision ranging between <NUM> micrometers (µm) and <NUM> depending on such factors as probe repeatability, machine accuracy, including thermal variations of the grinding machine <NUM>, and target surface finish of the crankshaft <NUM>. A feeler gauge <NUM> can be attached to the grinding wheel assembly <NUM> and physically touch a crankpin to measure the dimensions of the crankpin. The feeler gauge <NUM> can be directed to extend from the assembly <NUM> to contact the crankpin surface and, as the crankshaft is rotated about the C-axis, the gauge <NUM> can measure the crankpin.

The acoustic emission sensor <NUM> can be carried by the grinding wheel assembly <NUM> and used to monitor sound created when the grinding wheel <NUM> contacts the crankshaft <NUM>. The grinding wheel assembly <NUM> can include the acoustic emission sensor <NUM> in any one of a variety of locations. It can be helpful to position the acoustic emission sensor <NUM> as close to the grinding wheel <NUM> as possible to encourage a sufficient signal-to-noise ratio. For example, the acoustic emission sensor <NUM> can be fixed to an outer surface of the grinding wheel assembly <NUM> near the grinding wheel <NUM>. The acoustic emission sensor <NUM> can be a microphone tuned to a particular frequency range. In one implementation, the acoustic emission sensor <NUM> can be tuned to detect audible emissions in a frequency range of <NUM>-<NUM>. The acoustic emission sensor <NUM> can be a piezo-type acoustic emission microphone.

A computer processor <NUM> can provide input to and receive feedback from a number of components identified above. For example, the servo motors that control the movement of the machine bed <NUM> along the grinding wheel rails <NUM>, the movement of the grinding wheel assembly <NUM> along the infeed rails <NUM>, the operation of the spindle shaft <NUM>, and/or the electric motors of the headstock <NUM> and the footstock <NUM> can all receive an input signal from the computer processor <NUM>, such as a commanded motor speed and direction, and also provide an output signal to the computer processor <NUM>, such as actual angular position, angular shaft speed, and/or angular direction. The acoustic emission sensor <NUM> can provide output to the computer processor <NUM> in the form of a signal indicating an absence or presence of sound or a strength of sound. The computer processor <NUM> can be any type of device capable of processing electronic instructions including microprocessors, microcontrollers, host processors, controllers, and application specific integrated circuits (ASICs). It can be a dedicated processor used only to carry out the described methods or can be shared with other functionality carried out by the grinding machine <NUM>. The computer processor <NUM> executes various types of digitally-stored instructions, such as software or firmware programs stored in computer-readable memory. However, it should be appreciated that other implementations are possible in which at least some of these elements could be implemented together on a printed circuit board.

Turning now to <FIG>, a method <NUM> of determining a grinding wheel position and a position of a crankshaft surface is shown. The method <NUM> begins at step <NUM> by moving the touch probe <NUM> into contact with a crankshaft surface to determining an initial location position. The crankshaft surface for this embodiment of the method <NUM> will be described in terms of the crankpin of the crankshaft <NUM>. However, other crankshaft or workpiece surfaces are possible. The grinding wheel assembly <NUM> can be moved along the Z-axis so that the radial surface <NUM> of the grinding wheel <NUM> used to process the crankpin, such as by grinding or mill turning, is aligned with the crankpin along the Z-axis. The headstock <NUM> and footstock <NUM> can rotate the crankshaft about the C-axis to ensure that the touch probe <NUM> would not strike a crankpin if the probe <NUM> were moved along the X-axis. The touch probe <NUM> can then be moved along the X-axis so that an end of the probe is within the circle of crankpin rotation about the C-axis. The headstock <NUM> and the footstock <NUM> can then rotate the crankshaft about the C-axis in a first rotational direction until the crankpin contacts the touch probe <NUM>. A current angular position of the crankshaft <NUM> can be determined using the rotary encoders of the headstock <NUM> and the footstock <NUM>. The computer processor <NUM> can then record the angular position where the crankpin touched the probe <NUM>. The headstock <NUM> and footstock <NUM> can then rotate the crankshaft in the opposite rotational direction until the crankpin contacts the touch probe <NUM>. The computer processor <NUM> can then record the angular position of the crankshaft when the crankpin contacts the touch probe the second time and determine the position of the crankpin and/or the grinding wheel assembly <NUM> based on the difference between the two contact angles. The data indicating the position of the crankpin surface based on the physical probe measurement can be recorded in a computer-readable medium, such as random-access memory (RAM), having read-write capability. The headstock <NUM> and footstock <NUM> can rotate the crankshaft <NUM> a defined angular amount away from the crankpin and the grinding wheel assembly <NUM> can retract from the crankshaft along the X-axis. The method <NUM> proceeds to step <NUM>.

At step <NUM>, the grinding wheel <NUM> is moved toward the crankshaft <NUM>. If not already so positioned, the grinding wheel assembly <NUM> can be positioned so that the grinding wheel <NUM> is aligned with the crankpin along the z-axis such that motion of the assembly <NUM> along the X-axis will bring the grinding wheel <NUM> into contact with the crankpin. A current angular position of the crankshaft <NUM> can be determined using the rotary encoders of the headstock <NUM> and the footstock <NUM>. The headstock <NUM> and footstock <NUM> can rotate the crankshaft to a first angular position. The first angular position can be any value, but in this implementation the first angular position is <NUM> degrees. The spindle assembly <NUM> can move toward the crankpin at a fast rate until the grinding wheel <NUM> approaches the crankpin. After the spindle assembly <NUM> is within a predetermined range of the crankpin, the assembly <NUM> can move toward the crankpin at a slow rate until the grinding wheel <NUM> contacts the crankpin. The method <NUM> proceeds to step <NUM>.

At step <NUM>, the acoustic emission sensor <NUM> is monitored for sound emitted when the grinding wheel <NUM> contacts the crankpin. As the spindle assembly <NUM> moves along the infeed rails <NUM> along the X-axis toward the crankpin, the computer processor <NUM> can activate the acoustic emission sensor <NUM> so that the sensor <NUM> detects the absence/presence of sound and/or the intensity of emitted sound. When the acoustic emission sensor <NUM> detects sound, an output signal can be sent from the acoustic emission sensor <NUM> to the computer processor <NUM>. The computer processor <NUM> can then record the position of the grinding wheel assembly <NUM> in the X-Z plane when the assembly <NUM> contacts the crankpin at a first angular position (in this embodiment, zero degrees) based on the acoustic emission sensor <NUM> signal. The height of the grinding wheel <NUM> above the X-Z plane can be known or determined and the polar coordinates of the rotation axis (a) of the spindle <NUM> when the grinding wheel <NUM> contacts the crankpin can be determined. The data can be recorded in the computer-readable medium. In another implementation, the microprocessor <NUM> can monitor the electrical power consumed by the spindle drive motor <NUM> to determine when the grinding wheel <NUM> contacts the crankpin. As the spindle assembly <NUM> moves along the infeed rails <NUM> along the X-axis toward the crankpin, the computer processor <NUM> can monitor the electrical power consumed by the spindle drive motor <NUM> to detect a change in the electrical power. The change in electrical power can indicate when the grinding wheel assembly <NUM> contacts the crankpin. The method <NUM> proceeds to step <NUM>.

At step <NUM>, the grinding wheel <NUM> is moved away from the crankshaft and the crankshaft is rotated a defined angular amount about the C-axis. The headstock <NUM> and footstock <NUM> can rotate the crankshaft <NUM> a defined angular amount, such as <NUM> degrees, to a second angular position. The grinding wheel <NUM> can then be moved toward the crankpin as described with respect to step <NUM>, the computer processor <NUM> can record the position of the grinding wheel assembly <NUM> in the X-Z plane when the grinding wheel <NUM> contacts the crankpin at a second angular position based on the acoustic emission sensor signal. The measurement of the crankpin surface has been rotated into different angular positions can be repeated and, in one implementation, can be measured at four positions-<NUM> degrees, <NUM> degrees, <NUM> degrees, and <NUM> degrees. The measurements can be recorded in the computer-readable memory. In this implementation, the grinding wheel <NUM> contacts the crankpin at four angular positions. However, the quantity of angular positions at which the crankpin is contacted can be increased or decreased. For example, the quantity can be selected based on the condition of the crankpin surface. Crankpin surfaces that are less round or outside of specified dimensions by more than a determined amount can call for an increased quantity of angular positions at which the grinding wheel <NUM> is brought into contact with the crankpin whereas crankpin surfaces that are in better condition can involve fewer measurements. The method <NUM> proceeds to step <NUM>.

At step <NUM>, the computer processor <NUM> determines whether a sufficient number of measurements have been collected and, if so, determines a true position of the crankpin relative to the grinding wheel <NUM> based on the acoustic measurements. The position of the crankpin relative to the radial surface <NUM> of the grinding wheel can be determined using the acoustic sensor measurements at a plurality of angular positions. The throw and angle of the crankpin before grinding can be determined using one of a variety of techniques. In one implementation, the throw and angle can be determined by detecting the difference in positions where the grinding wheel touches the crankshaft surface at the two angles where the crankpin is most positive in the X plane and where the crankpin is most negative in the X plane (between <NUM>-<NUM> degrees) and determining an angle from the difference in positions where the grinding wheel touches the part with the crankpin up and with the crankpin down (<NUM> and <NUM> degrees). In another implementation, the location of the rough crankpin surface can be calculated using a regression technique, such as a least squares circle fit as described in British Standards (BS) <NUM>-<NUM>:<NUM>. In applying the least squares circle fit, grinding wheel contact positions can be interpreted using the axis path described in <CIT> assigned to Landis. Measurements of the crankpin relative to the grinding wheel <NUM> based on an output signal from acoustic emission sensor <NUM> can compensate for current thermal distortion of the grinding machine <NUM> as well as a changing radius of the grinding wheel <NUM> due to previously-carried-out grinding. The method <NUM> then ends.

It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

Claim 1:
A grinding machine (<NUM>) including one or more grinding wheels (<NUM>), comprising:
a workpiece holder (<NUM>) that releasably holds a crankshaft (<NUM>) and is configured to rotate the crankshaft (<NUM>) about a longitudinal axis (C);
a spindle assembly (<NUM>), that is moveable in at least two directions, including a spindle shaft (<NUM>) and a grinding wheel (<NUM>) attached to the spindle shaft (<NUM>); and characterised in that the grinding machine (<NUM>) comprises
an acoustic emission sensor (<NUM>) coupled to the grinding machine (<NUM>), wherein the grinding machine (<NUM>) is configured to monitor an output signal from the acoustic emission sensor (<NUM>), move the grinding wheel (<NUM>) into contact with the crankshaft (<NUM>) at a first angular position, detect contact between the grinding wheel (<NUM>) and the crankshaft (<NUM>) based on the output signal, determine a position of the grinding wheel (<NUM>) based on the detected contact between the grinding wheel (<NUM>) and the crankshaft (<NUM>), move the grinding wheel (<NUM>) away from the crankshaft (<NUM>), rotate the crankshaft (<NUM>) a defined angular amount, move the grinding wheel (<NUM>) into contact with the crankshaft (<NUM>) at a second angular position, determine a position of the grinding wheel (<NUM>) based on the detected contact between the grinding wheel (<NUM>) and the crankshaft (<NUM>), and determine a position of a crankshaft surface.