Turning – Process of turning
Reexamination Certificate
1998-12-14
2001-03-20
Wellington, A. L. (Department: 3722)
Turning
Process of turning
C082S001300, C082S001400, C082S158000, C082S904000
Reexamination Certificate
active
06202521
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the areas of controllable machine tools, active machining methods and controllers therefor. More specifically, it relates to an apparatus, method and controller for machining non-circular work piece profiles, such as on pistons for internal combustion engines.
BACKGROUND OF THE INVENTION
For some types of machined work pieces, it is desirable to have a non-circular profile (example: oval) where the positions of the major and minor diameters are precisely located on the work piece. For example, on pistons for internal combustion engines, such as in automobiles, lawnmowers, weed trimmers, leaf blowers, chainsaws, etc., it may be desirable to have the minor dimension substantially aligned with the wrist pin (the wrist pin rotatably connects the piston to the connecting rod). During, use, the piston may nonuniformly expand to a greater extent across the wrist pin dimension. By proper alignment of the major and minor diameters on the piston, this non-uniform expansion can be accounted for and the piston will take on a substantially circular shape upon reaching its equilibrium operating temperature. This results in better performance and may reduce noxious emissions.
Various machines are known for providing actively controlled machining. For example, in a paper entitled “Application Of An Actively Conti-oiled Magnetostrictive Actuator To Vibration Abatement In The Turning Process”, ASME 1995 DSC-Vol. 57-1 IMECE, by T. J. Sturos et al. it was suggested that a magnetostrictive actuator, such as made from a Terfenol-D material, may be used in a lathe to impart active control forces to a vertically disposed flexibly mounted tool holder. A position sensor was used to implement feedback control of the tool position. It was indicated by the authors that a 40% improvement in surface roughness was achieved during cutting via reducing tool chatter phenomena. U.S. Pat. No. 4,646,595 to Slee describes a machine tool which includes an actively driven machine tool (see
FIG. 4
) for machining piston profiles. A frequency generator produces a very high frequency ultrasonic signal which is modulated by a modulator
11
and fed to an ultrasonic transducer
13
. An axial sensor on the tool head provides feedback control of the tool. U.S. Pat. No. 5,085,109 to Hidehiko et al. teaches a system for machining non-circular work pieces having a second axis slider (
3
) which is slideably moved by a second axis servomotor (
5
) at high speed. However, in the Hidehiko et al. system, the slider (
3
) may undesirably tend to wear over time.
Another problem with machining non-circular profiles occurs when the frequency of the lathe changes during machining due to temperature changes, etc. During such events, it is desired to have an accurate input signal which is phase locked to the part rotation frequency.
Accordingly, there exists a need for a simple and cost effective method, apparatus and controller for providing high speed machining of non-circular work pieces. Furthermore, a need exists for a system where the generated output signal is insensitive to frequency changes.
SUMMARY OF THE INVENTION
In view of the above discussion, the present invention is an apparatus, method and controller useful for machining a non-circular profile on a work piece. The apparatus, method and controller are adapted for use in combination with a turning, center (ex. Lathe or other rotating equipment) having a frame, an x-y table capable of gross horizontal movements relative to the frame, a spindle-driven rotating shaft and a work piece securing chuck.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
According to the invention, an apparatus is provided for machining of a non-circular profile on a work piece, the work piece having an axis of rotation, the apparatus comprising at least one position sensor for deriving at least one position signal correlated with a rotational position of the work piece, a vibrating tool assembly further comprising; a rigid tool block, a tool holder including first and second ends defining, a longitudinal axis, the tool holder mounted to the block at the first end and adapted to receive a machine tool at the second end, the tool holder including an integral spring member for providing relative ease of movement at the second end of the tool holder in a transverse direction, the longitudinal axis of the tool holder being disposed substantially parallel to the axis of rotation, and an actuator (such as a solid state actuator—piezoelectric or magnetostrictive) arranged to impart vibrational motions to the tool holder along the transverse direction, a control system for receiving the at least one position signal and generating an output signal to the actuator, the control system including; means for adjusting a magnitude and phase of the at least one position signal and producing a magnitude and phase adjusted output signal, and an amplifier for amplifying the magnitude and phase adjusted output signal whereby a non-circular profile is machined on the work piece with minimum and maximum dimensions precisely located in desired positions and where a desired amount of ovality (difference between major and minor diameters) is achieved.
The control system preferably includes a controller for generating a two per revolution square wave directly from the at least one position signal. Signal conditioning means may be provided in the controller for manipulating the square wave signal to produce a two per revolution sinusoidal signal. Means for adjusting a magnitude and phase of the sinusoidal signal are also included in the control system for providing an adjusted output signal. An amplifier amplifies or attenuates the adjusted output signal. Preferably, the means for adjusting the magnitude and phase are manually operated by a user. The apparatus enables a non-circular profile to be machined on the work piece whose minimum and maximum dimensions are precisely located in desired positions with the desired amount of ovality achieved.
According to the invention, the tool holder is preferably longitudinally disposed and may include a dog bone-shaped cutout portion which minimizes rotation of the machine tool upon application of the active forces. In a preferred embodiment, the at least one sional is provided by first and the second sensors located on an end of the shaft. In order to minimize vertical movement of the tool thereby minimizing chatter, a vertical stiffening spring element may be mounted between the end of the tool holder and the block.
Most preferably, the means for generating the phase locked sinusoidal input comprises a plurality of band pass filters, such as center adjustable switched capacitor filters. Feedback means are preferably provided for adjusting the plurality of band pass filters. The feedback means may adjust a clock frequency provided to a plurality of switched capacitor filters.
Preferably, the vibrating tool assembly in accordance with the invention includes the tool block having an upright portion and a platform formed thereon, the tool holder being bolted to the platform at one end thereof, the actuator being mounted to a bracket assembly secured to a backside of the tool block on one end and threadedly connected to the tool holder on another, the actuator being received through a hole formed in the upright portion.
In accordance with the invention, a method for machining a non-circular profile on a work piece is provided which comprises the steps of positioning the work piece within a rotating chuck of a machine in a predetermined orientation, the work piece including an axis of rotation; providing at least one sensor for deriving, at least one input signal representative of a rotational position of the work piece, providing a tool block moveably mounted
Highfill, III John H.
Jensen William S.
Norris Mark A.
Rossetti Dino J.
Ergenbright Erica
Gnbius Michael M.
Lord Corporation
Wayland Randall S.
Wellington A. L.
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