Geometrical instruments – Gauge – With support for gauged article
Reexamination Certificate
2001-11-02
2003-05-27
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Gauge
With support for gauged article
C033S501020, C082S162000
Reexamination Certificate
active
06568096
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of measurement engineering and to the machine-working of workpieces to produce cylindrically-shaped workpieces; more particularly to the measurement of deviations of shape or form of nominally cylindrical, including conical and barrel-shaped, workpieces; and still more particularly to the machine-working or cutting of cylindrically-shaped workpieces from blanks having a longitudinal central axis that is unsymmetrical and/or positionally unstable with respect to a machining or cutting tool.
BACKGROUND OF THE INVENTION
Precision cylindrical workpieces, such as shafts and axles, are extensively used in present-day machines and mechanisms. Very often, deviations from roundness of these cylindrical parts greatly affects the effectiveness and efficiency of the machines incorporating such workpieces. For example, deviations from from roundness of journals causes vibration, noise, heating and other adverse phenomena in ball and roller bearings, and so greatly shortens their useful life. Roundness is equally important for such elements, as crankshaft necks, piston pins, electric motor commutators, etc.
STATE OF THE ART
Existing methods and devices are only capable of overcoming the problem caused by deviations from roundness in machined workpieces, and are capable of testing for such deviations in relatively small workpieces (generally, those that are up to 400 mm in diameter and up to 500 mm in length), while the workpiece is out of a machine tool that is used to cut or otherwise shape the workpiece into a cylindrically-shaped object; and only while the workpiece or object being measured is stationary, using a stationary roundness tester.
One known device for measuring the roundness of a workpiece while it is out of the cutting tool or other machine used to impart the rounded shape into a blank is disclosed in Russian Patent No. SU 1,623,573, which issued Feb. 24, 1987. The device disclosed there includes a frame mounted on four damped bearings for vibration elimination. A mount, having a turntable for a workpiece to be measured, is attached to a frame on which there are secondary shock dampers. A sensor with a fixing pen, or measuring stylus, which tracks and interacts with a surface of the workpiece, is fitted on a motor-driven sliding member. The pen or stylus is utilized for measuring various parameters relating to the deviation of certain dimensions of the workpiece, and the surface structure of the workpiece, from ideal roundness and straightness, as applicable. The pen or stylus tip is capable of movement in any direction within a rectangular-shaped work area.
The device of this reference, however, has a number of drawbacks, specifically:
—it is technically complex, and is not completely protected against vibration, which affects the accuracy of its measurements; and
—the device is not suitable for use in measuring large workpieces, such as calenders or forming rolls, in which deviations from roundness may have an effect on the quality of paper, foil, rolled products, etc. produced on machines incorporating such workpieces.
A device and method for measuring deviations from roundness of an object is also disclosed in U.S. Pat. No. 3,942,253, which issued May 3, 1974. The device of that reference includes a linear displacement-sensing element, radial locating support members, which are made as multi-stepped, self-adapting rocking levers that are symmetrically positioned with respect to the linear displacement-sensing element. When a workpiece rotates without axial movement, a measuring gauge of the device measures the deviation from roundness of the workpiece's cross-sectional profile.
This device of this reference also has a major limitation in that it can measure only one parameter of a cylindrical piece, namely the deviation from roundness. Measurement of only the deviation does not, however, give a full indication of the workpiece's shape, and so does not enable a complete determination of the precision of machining of a cylindrical workpiece, since other shape-related parameters along the axial length of the workpiece cannot be properly measured.
Precision machining of long cylindrical workpieces creates a number of problems because of the presence of steadying elements or rests positioned along the length of the workpiece or object, which are used for holding the workpiece steady and in place on a machining tool used to cut a cylindrically-shaped object from a workpiece blank . The presence of such steadying rests prevents precise positioning of the longitudinal axis of rotation of the workpiece with respect to the cutting tool. In fact, the presence of such steadying rests often leads to a transfer of deviations from roundness from a reference object to the machined object.
A steadying rest of the type mentioned above, is disclosed in Russian Patent No.
SU N2 1,660,929, which issued May 3, 1989. The steadying rest of that reference includes a body having a piston with a piston rod linked through a moving chain with an inverted V-type and a presser jaws. The moving chain is made as a rigid bar with stop members and an additional rod aligned with the main rod and designed to interact with the presser jaw through introduced spring-loaded rod. The apparatus functions as follows: the prismatic jaw is driven to the reference piece and positioned to grasp tightly the neck, then fixed so. After adjustment, the piece is placed in the machine tool and the piston is moved to press the inverted V-type jaw to the piece.
Simultaneously the secondary rod moves the piston, which presses the presser jaw to the piece by rotating it. After completion of machining, the piston is moved to the right, the presser and the prismatic jaws are taken off the piece.
The device of this reference has a number of shortcomings, which cause deviations of form to be transferred from the reference surface to the workpiece being machined. In addition, the steadying rest of this reference does not allow for the machining of large, heavy pieces, thereby severely limiting its use.
Another steadying rest, with self-adjusting supports, is disclosed in the journal
Stanki i instrument
, 1976, No. 7, at p. 22-23. In the body of the steadying rest disclosed there, there are two self-adjusting inverted V-blocks movable in a radial direction. The workpiece is pressed to them with its external (datum) surface through a spring-loaded stop. Additionally, there is a secondary support that is a pad made from a fluoroplastic material in the steadying rest's body, which functions to partially counterbalance the weight of the workpiece.
A limitation of this device is the spring-loaded horizontal stop, which presses the workpiece against self-adjusting bearings. If the machining datum surface has deviations from roundness, then this stop follows these deviations when the workpiece rotates, the stop must move for distances equal to datum surface's deviations from roundness. A still further limitation of this device is that it also does not allow for machining of large, heavy workpieces, thereby severely limiting its use.
Still another device for the machining of surfaces of revolution onto a workpiece having a longitudinal central axis that is unsymmetrical and/or unstable with respect to the machining tool during the machining is disclosed in Russian Patent No. RU N2 2,111,089, which issued Feb. 20, 1996.
Corrections to the workpiece shape are made by placing the cutting tool within the angle of supporting element shoes. The shoes and the tool are mounted on a single bracket, which is capable of rocking movement in a plane perpendicular to the workpiece's axis of rotation.
The device of this reference has a limitation in that the force of pressing the shoes and the tool against the workpiece surface depends on the elastic strain of a spring, which is not constant. This circumstance has a negative effect on the machining accuracy. Furthermore, the device does not allow for a run-out greater than 10 mm, as the bracket with the shoes can
Binder Yakov Isakovich
Gebel Iosif Davydovich
Nefedov Askold Ivanovich
Svitkin Mark Mikhailovich
Abelman ,Frayne & Schwab
Bennett G. Bradley
Obschestvo s Ogranichennoi Otvetctvennostju “Tekhnomash”
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