Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
1999-05-24
2001-06-12
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S005000
Reexamination Certificate
active
06244930
ABSTRACT:
SPECIFICATION
This invention relates to centerless grinding systems; and more particularly relates to a novel and improved control system for a centerless grinding machine in producing specific profiles or tapers in a workpiece.
Centerless grinding machines are used to grind the outer surface of a rod or wire to specified dimensions and surface finish. In a typical grinding operation, a straight length of wire is fed between two grinding wheels which rotate in the same direction at different speeds and which are separated at the point of tangency by a distance equal to the diameter of the finished product. The work wheel or grinding wheel is fixed and rotates at a higher speed than a regulating wheel, the latter being moved toward or away from the work wheel in a straight line and locked in place. When one end of the workpiece, or wire, is fed between the two wheels, it is caused to rotate as a result of contact with the regulating wheel and is ground due to the action of the higher speed work wheel against the outer surface. Customarily, the regulating wheel is tilted with respect to the rotational axis of the work wheel so that its rotational axis is aligned at an angle, referred to as the “tilt angle”, away from the rotational axis of the work wheel. Typically, the tilt angle is on the order of 1° to 3° and produces a resultant force component that causes the wire to move or be advanced in a linear direction between the wheels as it is being ground. The rate of advancement of the wire, or feed rate, basically is a function of the tilt angle as well as the regulating wheel speed and diameter. However, other external factors have a pronounced effect on the feed rate including the type and amount of coolant used, ambient temperature and humidity, type of wheel, wire material, diameter and uniformity as well as the amount of material removed. Accordingly, the feed rate may vary in an uncontrollable manner by 50% or more.
In the case of grinding a wire to a single diameter, the variations in feed rate become immaterial because a controlling factor is the gap between the two wheels which remains constant throughout the entire process. However, in profile grinding, such as, where one or more tapered sections are to be formed in the wire, there is an even greater tendency to undergo uncontrolled variations in feed rate due mainly to the added factor of regulating wheel spacing or retraction.
In the past, trial and error has been employed in which a slippage factor is combined with the conventional feed rate calculation to obtain a more realistic value of average velocity; however, this method requires constant monitoring of produced parts and periodic corrections to the regulating wheel rotational speed and spacing in order to obtain a close approximation to the desired profile. Another approach is disclosed in U.S. Pat. No. 5,480,342 to Bannayan et al in which both the position and feed rate of the wire are monitored by photoelectric cell detectors at widely spaced intervals along the bed, relatively speaking, and that information used to determine when the distance between grinding wheels should be changed and the rate at which that distance should be changed. Nevertheless, this approach presents numerous problems with respect to reliability of reading the movement of the wire past a photoelectric cell, the relatively wide spacing between cells and lagging and positioning errors which can result.
Another representative centerless grinder is disclosed in U.S. Pat. No. 5,674,106 to Cheetham in which photoelectric cells are utilized to sense the position and feed rate of the wire, the cells being mounted in slidable sensor banks which can be adjusted according to the length of the wire being ground but must calculate the actual position of the trailing end of the work piece between successive cells and compared to ideal position data to achieve the desired accuracy in the machined work piece profile.
The foregoing and other problems can be overcome by utilizing a position based system which is virtually feed rate independent in achieving the precise grinding of profiles having varying diameters with a high degree of accuracy. In particular, accuracy in grinding profiles is greatly enhanced by being able to calculate incremental changes in the gap based on the actual or known position of the work piece and not have to extrapolate between known positions or utilize trial and error in forming the desired profile.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide for a novel and improved method and apparatus for centerless grinding which is capable of accurately forming selected profiles in elongated articles, such as, wire.
Another object of the present invention is to provide for a novel and improved detection module for centerless grinding for accurately controlling incremental movement between a work wheel and regulating wheel in accordance with a specific profile to be ground.
It is a further object of the present invention to provide for a novel and improved method and means for centerless grinding of one or more tapered sections in a wire utilizing a position- based detection module to accurately control incremental changes in the gap formed between the grinding wheels in a highly efficient and dependable manner; and wherein the spacing between image detectors in a linear array for sensing the position of a wire as it is advanced along the linear array is such that each incremental movement of the grinding wheels in adjusting the gap therebetween is effected only in response to advancement of the wire past an image detector.
Broadly, in accordance with the present invention, there is provided an apparatus for grinding one or more tapered sections in a length of an elongated article by advancing the article axially through a gap formed between a rotating work wheel and rotating regulating wheel during a grinding cycle in which the gap is adjustable according to the diameter to which the article is to be ground, the improvement comprising drive means for rotating the wheels at a constant rate of speed during each grinding cycle, signal responsive means for incrementally adjusting the gap in a radial direction relative to axial advancement of the article through the gap, image detecting means upstream of the wheels through which the article is advanced including a series of image detectors for generating a succession of input signals in response to advancement of a trailing end of the article thereacross, and gap control means for generating and transmitting a plurality of output signals to the signal responsive means wherein each of the output signals is generated in response to receiving a series of input signals from the image detector means.
In a preferred form of the present invention, a novel and improved image detection module is placed in the path of advancement of the wire and in predetermined relation to the work wheel and regulating wheel to control a specific profile to be ground in the wire solely in response to sensing the position of the wire as it advances through the module. The module itself is in the form of a light chamber having a directed light source and image sensing linear array with a resolution of 200 pixels per inch or better, the array being of a length at least equal to that of the taper or profile being ground. Specifically, the module provides real time information to a central processing unit of current wire position which information is then used to command a stepper motor to move a previously computed number of steps at a selected constant speed. Since the regulating wheel motion takes place only after a confirmation signal is received that the wire has traveled a selected or programmed increment, the fact that each signal takes more or less time than the previous one becomes immaterial.
REFERENCES:
patent: 5480342 (1996-01-01), Bannayan et al.
patent: 5746644 (1998-05-01), Cheetham
Eley Timothy V.
Nguyen Dung Van
Reilly John F.
Star Guide Corporation
LandOfFree
Method and apparatus for centerless grinding does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for centerless grinding, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for centerless grinding will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2470573