Abstract:
Depth measuring apparatus especially useful for measuring the depth of cells formed in a material layer, such as a rotogravure printing cylinder. An ultrasonic transmitter/receiver is adjustably mounted to a coupling element which is adjacent a surface having cells therein whose depth is to be measured. The position of the ultrasonic transmitting/receiving unit is adjustable with respect to the coupling element so as to adjust the angle at which the ultrasonic beam is impinged upon the material layer with respect to the plane of the material layer. The coupling element itself also has adjustment means associated therewith for adjusting the angle at which the ultrasonic beam is impinged on the material layer with respect to the plane of wall portions of cells formed in the material layer.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present invention is directed to apparatus useful in practicing methods disclosed and claimed in copending application Ser. No. 371,467, filed June 19, 1973, now Pat. No. 3,885,422 and the method disclosed in application Ser. No. 219,991, filed in 1972, now Pat. No. 3,808,878. 
     BACKGROUND OF THE INVENTION 
     This invention relates to apparatus useful in sensing the depth of cellular pits or cells formed in a surface. The apparatus is particularly useful in the preparation of rotogravure cylinders. 
     In the production of rotogravure cylinders to be used in an intaglio printing process, a plurality of closely adjacently spaced cells or cup-shaped pits are formed in the cylinder surface, either by electromechanical means or by means of an etching process. During the printing operation, the cells formed receive the printing ink and establish varying intensities of color shade depending upon their volume, so that a desired pattern including respective variations of color tone intensity can be produced. Thus, the intensity of the print depends upon the quantity of printing ink contained in the individual cells, i.e. on the section area and/or the depth of the cells. Therefore, it is of principle importance in the production of the rotogravure cylinders that the cells be formed to have a desired depth and thus provide a faithful color reproduction of the image of an original. 
     It has heretofore been customary to sense and inspect engraved cells or etched cells with respect to their depth or their volume by means of a microscope. Furthermore, it is possible to scan and record the profile of a predetermined number of cells by using profile recorders and with the aid of a special stylus. The values obtained in this way can then be compared with an empirically established scale of values in order to determine whether the examined cells have the necessary depth. However, these measuring methods are extremely cumbersome and time-consuming. 
     There is disclosed and claimed in copending application Ser. No. 371,467, filed June 19, 1973, and application Ser. No. 219,991, filed in 1972, an improved method for determining the depth of cells formed in a material surface. In accordance with the method, cells of an individual region are scanned successively by a bundle of an ultrasonic beam which is projected onto the surface of the material layer in a plane perpendicular to the side walls or side wall portions of the cells and at a specific angle with respect to the surface of the material layer. A portion of the ultrasonic beam is reflected back towards a source by the side wall and bottom portions of the scanned cell regions so that the reflected portion of the ultrasonic beam is parallel to the incident beam. As explained in the above-identified copending patent applications, the intensity or amount of the reflected ultrasonic beam depends upon the size of the area of the wall of the cell and hence on the depth of the cell because with a given diameter of ultrasonic beam and with increasing wall size or depth of the cell, an increased portion of the incident ultrasonic beam is returned to the receiver and measured thereby. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     Accordingly, it is an object of this invention to provide apparatus for use in ultrasonically measuring the depth of cells formed in a material surface. 
     It is a more specific object of this invention to provide adjustable apparatus for generating and coupling an ultrasonic beam into cells formed in a material surface whereby the amount of the ultrasonic beam reflected parallel to the incident beam is detected and used as an indication of the depth of the cell. 
     Briefly, in accordance with one embodiment of the invention, there is provided an ultrasonic sensing head capable of both transmitting and receiving an ultrasonic beam. The ultrasonic sensing head is adjustably mounted within a housing which is adapted to be locked relative to the material layer surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional view of apparatus in accordance with the invention shown suitably positioned on the surface of a material layer; 
     FIG. 2 is a diagrammatic cross-section of a typical cell formed in the material layer, the depth of which cell is to be measured. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows one embodiment of apparatus in accordance with the invention, which apparatus is shown mounted in fixed relative position to the surface of a material layer such as a rotogravure printing cylinder. The apparatus includes a frame or a housing 2 which, on its side opposing the printing cylinder surface 9, is provided with a lateral aperature 16 to facilitate easy actuation and handling of the measuring device, as more specifically described hereinafter. A retainer rod 7 passes through the upper portion of the housing 2, which rod carries at its upper end a gripping element, such as a knurled wheel or a knurled disc 1. Interiorally of the housing, the retainer rod 7 is provided, for example, with a welded support washer 11 some centimeters under the upper housing wall. A compression spring 8 is interposed between the support washer 11 as one abutment surface and the inner face of the upper housing wall as a second abutment surface. Under the support washer 11 the retainer rod 7 is offset or bent, which configuration, although not essential, is advantageous. A coupling element 5 is provided as shown in FIG. 1 and preferably has a partly spherical or partly cylindrical shape, such as a hemispherical shape or a semi-cylindrical shape. The coupling element 5 is suitably attached to the lower end of the retainer rod 7, preferably so as to be rotatable about the lower end of the retainer rod. As shown, the retainer rod 7 holds the coupling element 5 centered relative to a particular vertical point (centerline 13) on the material layer surface 9 or on the rotogravure cylinder 6. 
     An ultrasonic sensing head 3 is placed, with an intermediate lubricant layer, such as a silicone oil layer, onto the outer (i.e. spherical or cylindrical surface of the coupling element 5 with the interposition of another coupling element 10 having its contact surface exactly adapted to the outer surface of the coupling element 5. The elements 5 and 10 may be formed of any suitable material which efficiently transmits ultrasonic beams and the elements 5 and 10 should be formed of materials which have the same or substantially the same index of refraction for ultrasonic beams. 
     The ultrasonic measuring head may be a conventional type standard ultrasonic combined transmitter/receiver, such as those manufactured by Branson Instruments Company, Stamford, Conn. The ultrasonic beam from such a transmitter can have a diameter, for example, of approximately 12.7 mm. This ultrasonic measuring transmitter/receiver 3 is positioned or aligned in such a way that the ultrasonic beam impinges upon the base point of the vertical centerline 13 on the surface of the material layer 9. The attachment of the ultrasonic measuring head 3 on the coupling element 5 is made, on the one hand, between the other coupling element 10 which contacts the ultrasonic emission surface of the measuring head 3 by means of a socket 14, or any equivalent positively locking attachment element. In accordance with the preferred embodiment of the invention, elastic tensioning retainer elements 4, which can, for example, be rubber or neoprene strips or even tension spring elements, are anchored in appropriate recesses 12 at the lower edge of coupling element 5, which lower edge can be slightly raised relative to the contact surface of the coupling element 5 on the material layer surface 9. These tensioning retainer strips 4 pass over a stud 15 or the like on the ultrasonic measuring head, such that the ultrasonic measuring head is urged against the second coupling element 10 which, in turn, is pressed against the coupling element 5. As previously pointed out, a lubricant layer is maintained between the mating surfaces of the coupling elements 5 and 10 and can be a silicone oil composition. If desired, means such as a reservoir can be provided for continuously replenishing the lubricating oil layer. 
     In operation, the housing 2, in combination with the retainer rod 7 and the lower coupling element 5 attached thereto, is brought into a predetermined relative position to the material layer which, for example, is a rotogravure printing cylinder. Although not necessary, the outer lower housing edge may thereby contact the material layer surface 9. In view of the action of the compression spring 8, the lower contact or abutment surface of the coupling element 5 contacts the material layer surface 9 with a certain pressure. In accordance with a preferred embodiment, a continuously maintained lubricant layer is maintained between the lower contact or abutment surface of coupling element 5 and the surface of the material layer 9. This lubricant layer can be a silicone oil composition, for example, and suitable reservoir means may be provided for maintaining a constant supply of the lubricant. The lubricant permits the apparatus to be smoothly and easily shifted from one sensing position on the surface 9 of the rotogravure cylinder to the next sensing position. 
     In order to determine the depth, such as the etched depth of ink receiving cells formed in the surface of the material layer such as the rotogravure cylinder, the ultrasonic measuring head or transmitter/receiver provided with the second coupling element 10 is attached and fixed on the lower coupling element 5 in a given angular position by means of the resilient tensioning retainer elements 4. This angular position may be varied in a relatively easy manner by shifting the sensing head 3 and the coupling element 10 with respect to the coupling element 5, whereby the mutually contacting abutment surfaces of the two coupling elements 5 and 10 slide upon each other via the intermediate lubricating film. However, the tensioning retainer elements 4 retain the measuring head 3 with a sufficiently great bias force against the lower coupling element 5 that the measuring head cannot shift by itself. Accordingly, the measuring head 3 is adjusted, for example, in accordance with the directions according to the methods described in the above-mentioned copending patent applications, to a predetermined angle either relative to the centerline 13 or relative to the surface of the material layer or with respect to a tangent to the base point of the perpendicular line 13 and the surface of the material layer. In principle, this angle can be any angle between 0° and 90°. The respective limits should be avoided because it is difficult to obtain verifiable clear measuring results at these limits. On the other hand, proper results are obtained in the angular range of between 10° and 70°. For reasons of geometrical optics, which are explained in more detail in the specifications of the above-mentioned copending patent applications, an optimum yield of a measured value signal is achieved at an angle of projection of about 30° relative to the perpendicular line 13. This position corresponds approximately to the position of the measuring head as shown and illustrated in FIG. 1. Once the measuring head is adjusted to optimum values, an adjustment of the ultrasonic beams to the cells to be measured in the surface of the material layer may be effected simply by rotating the knurled wheel 1. That is, the knurled wheel 1 is rotated so as to rotate the coupling elements 5 and 10 and hence the ultrasonic sensing head 3 to the point where the ultrasonic beam impinges upon a cell in a plane which is perpendicular to the plane of the side wall portions of the cell. Maximum reflection of the ultrasonic beam by the side walls and the bottom portions of the cells will be achieved when the plane of the impinging ultrasonic beam is at 90° or perpendicular to the plane of the side walls of the cells. The lower coupling element 5 under the action of the spring 8 is always held in firm contact with the surface of the material layer 9. 
     As explained in the previously mentioned copending patent applications, and as can be visualized by referring to FIG. 2, the ultrasonic beam S impinges upon the material layer surface 9 at an angle θ, which as explained previously, can be between 0° and 90° but, in accordance with one embodiment, is approximately 30°. Portions of the ultrasonic beam S strike the upper portion of the surface 9 and are reflected off the surface at some angle. Certain other portions of the ultrasonic beam S impinge upon the walls of the cell and are reflected to the bottom of the cell which in turn reflects the ultrasonic beam back out in a direction parallel to the incoming beam. Likewise, portions of the ultrasonic beam strike the bottom of the cell and are reflected from the bottom to the side wall and are reflected by the side wall back in a direction parallel to the incoming beam. As explained in the above-mentioned copending patent applications, the portion of the incoming ultrasonic beam which is reflected parallel to the incoming beam is proportional to the area of the wall portions W and hence proportional to the depth of the cell and detection and measurement of the reflected portions of the ultrasonic beam serve as an indication of the depth of the cell. 
     Although the invention has been described with reference to particular preferred embodiments, it is obvious that certain modifications can be made to these preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention.