A DEVICE FOR MEASURING THE LENGTH OF A CONTACT SURFACE

Abstract: A device (2) for measuring contact-length, i.e. the spacial extension of the abutment surface between two mutually abutting bodies, of which at least one is compressible, the device comprising a thin sensor (3) which is introduced between the mutually abutting bodies. The sensor (3) comprises an electrically short-circuiting element (5), an electrically resistive element (6) and an intermediate, slotted, non-conductive space element (9). When measuring a contact-length, the short-circuiting element (5) is pressed through the slot in the spacer element (9), against the resistive element (6) along a distance which corresponds to the contact-length. The change in resistance across the resistive element (9), measured by a measurement-value indicating means (4) connected to the sensor (3), therewith constitutes a measurement of the contact-length. An advantage is afforded when the resistive element (6) has the form of a very thin copper wire disposed in closely adjacent loops. In other embodiments of the device, the contact-length is measured by capacitive and optical measuring methods respectively.

Description: A DEVICE FOR MEASURING THE LENGTH OF A CONTACT SURFACE This invention relates to a contact-length meter, by which is meant a device which is operative to measure the geometric extension of the surface of abutment or mutual contact between two mutually adjacent bodies which may both be in motion, one in motion and the other stationary, or both stationary. The bodies may both be compressible in the vicinity of the contact surface, or solely one body compressible, and have mutually facing surfaces which present either a single curvature or a double curvature, or of which bodies one presents either a single or a double curvature and the other body is planar. The extension of the contact sur- face in a given direction is measured or determined by placing sensors, forming part of the meter, between said bodies along said direction. A primary element incorporated in the sensor is therewith influenced in a manner which will enable the length of said extension to be read-off from measurement-value indicating means connected to the sensor. Background Art There are a number of contexts in which reason is found to measure the extension or length of an abutment surface between two mutually adjacent bodies, of which at least one is compressible. Such contexts are found in mutually rotating rolls, rocking rolls or inter- mittently abutting rolls, which may be cylindrical or conical, straight or cambered and have parallel or offset longitudinal axes. The context concerned may also be one in which a roll of the aforesaid kind lies continuously or intermittently against a flat surface. Bodies of the aforesaid kind are found, inter alia, in several types of roll constructions, for instance laminating equipment, paper machines and printing presses. The mutually abutting bodies may have smooth or patterned surfaces. The invention is particularly suitable for application in printing presses. It is important in the case of roll arrangements to accurately sense and control the pressure acting be¬ tween the rolls or between a roll and a flat surface, thereby to control, inter alia, spreading of ink or some other liquid transferred between the bodies or to control the layer thickness of said ink or liquid. The aforesaid abutment surface is a measurement of this pressure. It is of particular interest to measure the length extension of the abutment surface at right angles to the longitudinal axis of the roll or rolls. Hitherto, no simple and reliable devices or methods are available for measuring either the pressure between the rolls or the length or spacial extension of the abutment surface. One method known within the printing industry is to stop two counter-rotating liquid-laden rolls and then rotate the rolls slowly through part of one revolution. This results in a visible stripe in the liquid layer of the rolls, this stripe deriving from the aforesaid stationary state and the width of said stripe consti¬ tuting the extension of the abutment surface perpen- dicular to the longitudinal axis of the rolls. This method is time consuming and the accuracy with which the width of the stripe is measured is small, and the method cannot be used with rolls to which no liquid is applied or to which only transparent liquid, such as water, is applied. Another method used within the printing industry invol¬ ves introducing a strip of paper or foil between slowly rotating rolls and, when the rolls have stopped, with- drawing one of the strips and judging by experience the value of the roll pressure or the extension of the abutment surface. This method is unreliable and cannot be repeated independently of the operator. None of the aforesaid methods can be applied suitably on rolls which are difficult to reach or rolls situated in poor light conditions or in dirty environments. The simple method, conceivable in practice, of introducing, for instance, a paper sheet into the roll nip, pressing the rolls towards one another, separating the rolls and reading the abutment imprint on the paper cannot be carried out in practice, since the rolls concerned are most often in fixed positions. The Japanese layout print JP 61-702 teaches a flexible sensor which is attached to a body and by means of which contact between said body and another body can be detected. This sensor is able to disclose whether such contact exists, practically along the whole length of the sensor. The sensor is primarily intended for detec- ting contact between various parts in an automated manufacturing process, for instance between an indus¬ trial robot and components co-acting therewith, and is unable to measure the geometric extension of the abut¬ ment surface between two bodies, and consequently cannot be used for the purpose of this invention. The Object of the Invention and the Most Important Characterizincf Features Thereof The drawbacks of the aforesaid methods are avoided by the inventive device, in that there is used a thin, mechanically durable sensor which is composed of simple components, which has good accuracy and which enables a fully novel measuring method to be carried out quickly and readily in not-readily reached places, dirty places and poorly lit places. The invention will be described in more detail in the following with reference to a number of preferred exemplifying embodiments thereof and with reference to the accompanying drawings. Similar components in the various Figures of the drawings are identified with mutually the same reference signs. Figure 1 is a cross-sectional view of two mutually adjacent cylinders, both of which are compressible, in which the reference numeral 1 identifies the length or spacial extension of the abutment surface perpendicu¬ larly to the longitudinal axis of the cylinders. Figure 2 is a cross-sectional view of two mutually adjacent cylinders, of which one is compressible and the other non-compressible. Figure 3 is a cross-sectional view of a compressible cylinder which abuts a non-compressible flat surface. Figure 4 is a cross-sectional view of a non- compressible cylinder which abuts a compressible flat surface. Figure 5 is a cross-sectional view of one of a number of further instances in which two bodies having curved surfaces have a common abutment surface, in this case a non-compressible sphere in abutment with a compressible body having a dish-shaped surface. In all embodiments illustrated in Figures 1-5, the two bodies can be either movable or immovable relative to one another. Furthermore, the illustrated special extension 1 can vary along the extensions of respective abutting bodies at the surface of mutual contact. Figure 6 illustrates an inventive contact-length meter 2 provided with a sensor 3 and measurement-value indicating means 4. Figure 7 is a longitudinal, cross-sectional view taken in the thickness-direction of the sensor 3 ac¬ cording to one embodiment. The sensor of this embodi- ment comprises an elongated, electrically short-cir¬ cuiting element 5, an elongated electrically-resistive element 6 having a well-defined geometric pattern with end points 7 and 8, and a non-conductive spacer element 9 which is slotted along its length and placed between said two elements. Figure 8 is a sectional view of the sensor 3 shown in Figure 7, taken at right angles to the longitudinal axis of the sensor. Figure 9 illustrates an example of the use of the contact-length meter 2, namely a use in which the sensor 3 illustrated in Figure 7 and 8 is introduced in between two mutually abutting rolls, by rotation of the rolls. Because, inter alia the sensor 3 has a given thickness in the order of some tens of a millimeter, the length 10b of the element 5 which is activated and measuringly operative during said abutment will deviate slightly from the true spacial extension 10a of the abutment surface, to which corrections are made with a correction factor including, inter alia, the relation of the thickness of the sensor 3 to the respective radii of the two cylinders. If the cyliders are ex¬ changed for other bodies, the correction factor will be contingent on the radii of curvature of said bodies at the abutment surface. Figure 10 is a longitudinal cross-section through the width of another embodiment of the sensor, this sensor comprising two mutually parallel, elongated light guides 11 and 12, and an elongated, light-impermeable element 13 which extends parallel with said light guides. The light guides 11 and 12 are only permeable to light at the short-ends thereof at which they are attached to the measurement-value indicating means 4, and at the mutually facing, long surfaces of said guides. The remaining surfaces of the light guides are more or less reflective. Figure 11 is a sectional view of the sensor 3 shown in Figure 10, at right angles to the longitudinal direction of the sensor 3. When carrying out a measuring operation, the sensor 3 is introduced between the two bodies in any one of Figures 1-5, to an extent such that the end of the sensor 3 distal from the measurement-value indicating means 4 will have passed the mutual abutment surface of the bodies. When taking measurements with the aid of the sensor 3 illustrated in Figures 7 and 8, the short-circuiting element 5 is pressed through a slot in the spacer element 9, into contact with the resistive element 6 along a path constituted essentially by the spacial extension of the abutment surface between the bodies in the longitudinal direction of the sensor 3. It is possible with the aid of known technique to readily measure the resistance between the terminal or end points 7 and 8, on the one hand in the absence of abutment of said bodies and on the other when the sensor 3 is inserted between the bodies, wherewith in this latter case the resistance will fall as a result of the short-circuiting element 5 being pressed along a part of its length towards and against the resistive element 6, this resistance providing a measurement of said extension. An advantage is afforded when the resistive element (6) consists of a very thin, copper wire which is disposed in closely adjacent and mutually parallel continuous loops of mutually equal lengths, these loops being positioned perpendicularly to the longitudinal direction of the resistive element (6) . It will be understood that the aforesaid sensor can be modified for use with capacitive measuring processes. When the sensor 3 has the form illustrated in Figures 10 and 11, light is transmitted from the measuring- value indicating means 4 through the light guide 11, this light, when the sensor 3 is not subjected to load from said bodies, reaching the light guide 12, which returns the light to the indicating means 4. On the other hand, when the sensor 3 is placed between mutu¬ ally abutting bodies, the light-impermeable element 13 is pressed in between the light guides 11 and 12 and screens the transfer of light between said guides to an extent which corresponds to the spacial extension of the abutment surface. The value of this screening effect can be readily measured with the aid of the measuring-value indicating means 4, using known techniques. In order to enable the sensor 3 to be used readily and reliably in an industrial environment, said sensor will preferably be made from a tough and stretch-durable material. The measurement-value indicating means 4 is provided with means for analog or digital presentation of measuring values, for manual or automatic locking of measured values, for signalling that the measuring process is completed and may also incorporate illumina¬ tion means. The measurement-value indicating means 4 may readily incorporate the aforesaid facility for correcting measured values of the abutment-surface extension to correct values, described with reference to Figure 9. It will be understood that the aforedescribed contact- length meter 2 can be used for calculating the abutment pressure between two bodies on the basis of measured values relating to the spacial extension of the abut¬ ment surface, the radius of curvature of respective bodies and their respective compressiblity.

Claims: CLAIMS 1. A device for measuring (2) the spacial extension of the abutment surface between two mutually adjacent bodies, which bodies may either both be movable, or solely one of said bodies may be movable, or both of said bodies may be stationary, and which bodies, at and adjacent the abutment surface, are both compressible or solely one of said bodies is compressible, and have mutually facing surfaces which are either both single- curved or double-curved or the one is single or double- curved and the other planar, c h a r a c t e r i z e d in that the device includes a measurement-value in¬ dicating means (4) and a sensor (3) which is connected to said means and which is intended for insertion between said abutting bodies, said insertion being effective to activate a primary element incorporated in the sensor (3) such as to give a measurement of the spacial extension of said abutment surface in the longitudinal direction of the sensor (3). 2. A device according to Claim 1, c h a r a c ¬ t e r i z e d in that the sensor (3) has provided along essentially the whole of its length an electrically short-circuiting element (5), an electrically resistive element (6) extending parallel with said element (5) and having terminal or end points (7, 8) , and a non- conductive, slotted spacer element (9) positioned be¬ tween said elements, said short-circuiting element (5) being intended to be pressed through said slot against the resistive element (6) along substantially the whole extension of the abutment surface, wherein the resul¬ tant change in the resistance between the points (7, 8) measured by the measurement value indicating means (4) constitutes a measurement of the spacial extension of said abutment surface. 3. A device according to Claim 2, c h a r a c - t e r i z e d in that the resistive element (6) is a very thin copper wire which is disposed in closely adjacent and mutually parallel continuous loops of mutually equal lengths; and in that the loops are positioned perpendicularly to the longitudinal axis of the resistive element (6). 4. A device according to Claim 1, c h a r a c ¬ t e r i z e d in that extending substantially along the whole length of the sensor (3) are two mutually paral- lei light guides (11, 12) which are connected to the measurement-value indicating means (4) and which are permeable to light solely through mutually facing surfaces and surfaces facing the indicating means (4); in that extending parallel with said light guides is a light-impermeable element (13) which is intended to be pressed in between the light guides (11) and (12) essentially along the whole extension of the abutment surface, wherein the light transmitted from the measurement-value indicating means (4) to the light guide (11) and from said light guide to the light guide (12) and from said light guide back to the measurement- value indicating means (4) decreases to an extent which constitutes a measurement of the spacial extension of said abutment surface. 5. A device according to Claim 1, c h a r a c ¬ t e r i z e d in that the sensor (3) includes a capaci¬ tive primary element, the change in capacitance of which when in abutment with the bodies measured by the measurement-value indicating means (4) constitutes a measurement of the spacial extension of said abutment surface. 6. A device according to any one of the preceding Claims, c h a r a c t e r i z e d in that correction of the measured spacial extension of the abutment surface to a correct value is effected manually or automati¬ cally in the measurement-value indicating means (4) with the aid of values inserted in said means relating to the thickness of the sensor (3) and the radius of curvature of respective mutually abutting bodies at said abutment surface. 7. A device according to any one of the preceding Claims, c h a r a c t e r i z e d in that the measurement-value indicating means (4) is provided with a facility for manually or automatically locking the measured values, signalling that the measuring opera¬ tion is completed, and also for illuminating the measurement-value display. 8. A method for determining the abutment pressure of two mutually abutting bodies in which there is utilized the value of the spacial extension of the abutment surface as measured by a device according to any one of the preceding Claims, c h a r a c t e r i z e d by calculating the abutment pressure as a function of the spacial extension of the abutment surface, the radius of curvature of respective bodies, and the compres- sibility of respective bodies at the abutment surface.

Inventors: CRONVALL LEIF, CRONVALL, LEIF
Applicants: ELECTRIC MEASUREMENT DEVICE AB
Application year: 1990
Main classification: G01B21
IPC codes: G01B7, G01B11, G01B21