Method for detecting roller breakdowns in roller hearth kiln systems

Abstract: To detect roller breakdowns in a roller hearth kiln, a light shielder (15) is provided at the follower end of each roller (2) and two sets of light transmitters (20,21) and light receivers (22,23) are provided on two straight lines between which the axis of rotation of each shielder (15) is positioned. Normally the light rays (A,B) transmitted from said light transmitters to said light receivers are both periodically blocked. If they are not both periodically blocked, it is assumed that at least one of the rollers has broken down.

Description: BACKGROUND OF THE INVENTION The present invention relates to a detector for detecting roller breakdowns in a roller hearth kiln used to sinter ceramics. In general, this type of roller hearth kiln includes a number of rollers arranged through the kiln wall, each roller being provided on its one side with a driving sprocket adapted to be driven by an endless chain. If one of the rollers breaks down in the kiln, then such a roller hearth kiln can never provide any smooth feeding of a workpiece over that roller. One typical method for detecting a roller breakdown is set forth in Japanese Patent Publication No. Sho 56-14951 (14951/1981). According to this method, a metal sheet is attached to the follower end of each roller. When the roller breaks down, the metal sheet moves under the action of a spring in the axial direction of the roller. Then, a proximity switch or the like senses such a movement to detect the rollers breakdown. Because of needing a device for driving the rollers, while axial pressures are always applied to them by means of springs, this method has difficulty in its application to a roller hearth kiln of the structure wherein the rollers are merely supported by backing rollers. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a reliable and rapid detection of a breakdown of at least one of rollers arranged in a roller hearth kiln whenever it occurs. Another object of the present invention is to provide a detection of a roller breakdown with a simplified roller-supporting structure. A further object of the present invention is to provide a reliable detection of a roller breakdown, using optical sensors in place of mechanical sensors such as limit switches. According to one aspect of the present invention, there is provided a method for detecting roller breakdowns in a roller hearth kiln, wherein; a light shielder is provided at the follower end of each roller in said roller hearth kiln, and two sets of light transmitters and two sets of light receivers are provided on two straight lines between which the axis of rotation of each shielder is positioned, whereby whenever light rays transmitted from said two sets of light transmitters to said two sets of light receivers are not periodically put on and off, at least one of said rollers is taken as breaking down. According to another aspect of the present invention, there is provided an apparatus for detecting roller breakdowns in a roller hearth kiln, comprising in combination: a group of rollers arranged side by side in said kiln in its tunnel direction, means for rotating said rollers of said group of rollers in phase or at the same angles of rotation, recessed shielders provided at ends of said rollers, a first light transmitter for emitting a light ray which traverses a position lying above the axis of each roller, a position inside of the outermost diameter of each shielder and a position eccentric with respect to the axis of each roller, said light ray being either passed in the vicinity of each shielder in a direction normal to the axis of each roller on a plane defined by said group of rollers or cut off by each shielder depending upon where each shielder turns, a first light receiver located at a position above the axis of each roller and capable of receiving said light ray emitted from said first transmitter, a second light transmitter for emitting a light ray which traverses a position below the axis of each roller, a position inside of the outermost diameter of each shielder and a position eccentric with respect to the axis of each roller, and a second light receiver located at a position below the axis of each roller and capable of receiving the light ray emitted from said transmitter. In preferred embodiments, the shielder may be of either a semicircular shape or a fan shape in cross section. The shielder is attached to the follower end of each roller. The shielder may be an integral part of the roller. Alternatively, the shielder may be provided separately from the roller. The light rays may be laser beams or visible or infrared rays. In the system according to the present invention, the first and second transmitters and the first and second receivers may be located in each of zones provided over a given length in the longitudinal direction of the kiln. The first or second transmitter and the first or second receiver may be located on both ends of the kiln, as viewed in its longitudinal direction. The means for rotating the rollers in phase may be a driving chain. The driving chain may then be a double-driving chain comprising a first chain for driving every other one of roller groups and a second chain for driving every another one. When the rollers turn normally, the light rays transmitted from the first and second transmitters to the first and second receivers are periodically cut off by the shielders. In other words, the two light rays are repeatedly and precisely transmitted and cut off in a constant cycle. If the light rays are put on and off in a constant cycle, then the rollers turn normally. Whenever at least one of the rollers breaks down, at least one of the light rays is cut off by the breaking-down roller. Thus, the roller breakdown can be reliably detected by signals from the first and second receivers which are designed to sense that at least one of the light rays is continuously cut off with time. Acordingly, the invention according to a further aspect is defined in claim 15. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained in greater detail, by way of example, with reference to the accompanying drawings, in which: - FIGURE 1 is a side view illustrating a detection zone in a roller hearth kiln according to one embodiment of the present invention, FIGURE 2 is an enlarged view illustrating a zone shown at II in FIGURE 1, FIGURE 3 is a cross-sectional view showing a roller hearth kiln system according to the present invention, FIGURE 4 is an enlarged view illustrating a zone shown at IV in FIGURE 3, FIGURE 5 is a perspective view of one example of the shielder, FIGURE 6 is a perspective view of another example of the shielder, FIGURE 7 is a time chart in which the input signals of the receivers are compared with each other between when a roller turns normally and when a roller breaks down, FIGURE 8 is a view illustrative of the relation between the angle of the shielder and light rays, and FIGURE 9 is a view illustrative of the relation between a comparative shielder and light rays. PREFERRED EMBODIMENT OF THE INVENTION Embodiment of the invention will now be described by way of example with reference to drawings. As illustrated in FIGURE 3, a number of ceramic rollers 2 in the form of hollow pipes are arranged side by side through a kiln wall 1 of a roller hearth kiln and at positions lying intermediate between its top and its bottom, and rotate to carry a piece to be sintered thereover, while that piece is sintered. Each of the rollers 2 is held at one end 2 a by driving means 3 and supported at the other end 2 b by supporting means 5. The driving means 3 includes a driving shaft 8 rotatably supported on a supporting frame 6 through a bearing 7. The driving shaft 8 is connected to a driving motor, not shown, through a sprocket 9 fixed at its end and a chain wound around it. The driving shaft 8 is connected to the one end 2 a of the roller 2 by a holder 13. Thus, a driving force is transmitted from the driving motor to the one end 2 a of the roller 2 by way of the chain, sprocket 9, driving shaft 8 and holder 13. A roller, not shown, located adjacent to the roller 2 shown in FIGURE 3 is fixed to a sprocket 10. The sprockets 9 and 10 are located at positions at which they do not interfere with each other. Thus, a group of sprockets 9 are arranged relative to a group of sprockets in the longitudinal direction of the kiln. The supporting means 5, on the other hand, is rotatably supported by two backing rollers 18 located adjacent to the other end 2 b of the roller 2. The backing rollers 18 are rotatably attached to a fixed shaft 17 through a bearing, not shown, said shaft 17 being attached to a bracket 16 fixed to the kiln wall 1. The roller 2 is provided at the other end 2 b with a light shielder 15 which is coaxial with the axis of the roller 2 and is of a semicircular shape in cross section. As shown in FIGURE 1, the shielders 15 attached to the rollers 2 arranged side by side in the longitudinal direction of the kiln are all in phase. Referring now to FIGURE 1, first and second light transmitters 20 and 21, e.g., laser beam transmitters, are located at one end of a detection zone C for detecting roller breakdowns in the roller hearth kiln. The detection zone C has at the other end first and second light receivers 22 and 23 for receiving laser beams emanating from the transmitters 20 and 21. In a state shown in FIGURE 1, a laser beam, shown at A emitted from the first transmitter 20 located above the rollers' axes travels over the rollers' axes and reaches the first receiver 22. On the other hand, a laser beam, shown at B , emitted form the second transmitter 21 located below the rollers' axes is cut off by the light shielders 15, so that it cannot reach the second receiver 23. Reference will now be made to the reason why two sets of the first transmitter 20/receiver and the second transmitter 21/receiver are provided. If only a single transmitter/receiver set is provided, then any roller breakdown may not be detected. This is because assuming that a roller breaks down and stops and rests at an angle at which the laser beam transmits through it (i.e., at an angle at which the laser beam is not cut off by the shielder 15), then the laser beam is not cut off by that breaking-down roller and is periodically intercepted by the remaining, normally turning rollers. In consequence, the laser beam reaching the receiver is periodically put on and off. Each of the shielder includes a recess through which light transmits. In the instant embodiment, the shielder is of a semicircular shape in cross section, as illustrated in FIGURE 6. Another shielder 32 may be used, which is of a fan shape in cross section, as illustrated in FIGURE 5. In the instant embodiment, the shielder 15 includes a recess through which light transmits, with the rest cutting off light. This is because assuming that the shielder is formed of a thin sheet 34, as shown in FIGURE 9, and rests at such a position as again shown in FIGURE 9 when a roller breaks down, both the laser beams emitted from the first and second transmitters 20 and 21 transmit through the breaking-down roller without cut off by the thin sheet 34, so that they produce no influence upon input signals periodically put on and off at the first and second receivers 22 and 23, failing to detect the roller breakdown. According to the instant embodiment, whenever at least one of the laser beams emitted from the first and second transmitters 20 and 21 is received by the corresponding receiver 22 or 23, the other laser beam is cut off by the shielders 15. The first and second receivers 22 and 23 convert the on and off signals of the laser beams received there to electrical signals, which are in turn sent to a control circuit, not shown. In this control circuit, whether or not roller breakdowns occur is detected on the basis of the electrical signals. When the rollers 2 turn normally, the laser beams emitted from the first and second transmitters 20 and 21 are alternately cut off by the shielders 15 in a constant cycle. In this case, since the shielder 15 turns as illustrated in FIGURE 8A, the signals received by the first and second receivers 22 and 23 are put on and off in a constant cycle, as illustrated in FIGURE 7A. The control circuit takes the rollers as turning normally, whenever the output signals of the first and second receivers 22 and 23 are put on and off in a constant cycle. Whenever any one of the rollers 2 breaks down, the shielder 15 attached to the other end 2b thereof stops so that at least one of the laser beams emitted from the first and second transmitters 20 and 21 is cut off, even though the remaining rollers 2 rotate. For instance, when the roller 2 stops at such a position as shown in FIGURE 8B, such signals as depicted in FIGURE 7B are inputted to the first and second receivers 22 and 23. When the roller 2 stops at such a position as depicted in FIGURE 8C, on the other hand, such signals as depicted in FIGURE 7C are inputted to the first and second receivers 22 and 23. For that reason, whenever any one of rollers 2 breaks down, the laser beam sensed by the first or second receiver 22 or 23 is never put on and off in a constant cycle, thus allowing the control circuit receiving the signals from the receiver 22 or 23 to take at least one of the rollers 2 as breaking down. This provides a reliable detection of roller breakdowns. In the embodiment as described above, laser beams of improved rectilinearity are used. It is to be understood, however, that in order to detect roller breakdowns according to the present invention, other light rays such as infrared or visible rays may be used. The foregoing embodiment has been described as being designed to detect breakdowns of rollers arranged in the detection zone positioned over a given length in the longitudinal direction of the roller hearth kiln. In the case of a kiln of short length, however, rollers arranged over its full length may be detected simultaneously.

Claims: A method for detecting roller breakdowns in a roller hearth kiln, wherein: a light shielder is provided at the follower end of each roller in said roller hearth kiln, and two sets of light transmitters and two sets of light receivers are provided on two straight lines between which the axis of rotation of each shielder is positioned, whereby whenever light rays transmitted from said two sets of light transmitters to said two sets of light receivers are not periodically put on and off, at least one of said rollers is taken as breaking down. An apparatus for detecting roller breakdowns in a roller hearth kiln, comprising in combination: a group of rollers (2) arranged side by side in said kiln in its tunnel direction, means for rotating said rollers (2) of said group of rollers in phase or at the same angles of rotation, recessed shielders (15; 32; 34) provided at ends of said rollers (2), a first light transmitter (20) for emitting a light ray (A) which traverses a position lying above the axis of each roller (2), a position inside of the outermost diameter of each shielder (15; 32; 34) and a position eccentric with respect to the axis of each roller (2), said light ray (A) being either passed in the vicinity of each shielder (15; 32 ;34) in a direction normal to the axis of each roller (2) on a plane defined by said group of rollers (2) or cut off by each shielder (15; 32; 34) depending upon where each shielder (15; 32; 34) turns, a first light receiver (22) located at a position above the axis of each roller (2) and capable of receiving said light ray (A) emitted from said first transmitter (20), a second light transmitter (21) for emitting a light ray (B) which traverses a position below the axis of each roller (2), a position inside of the outermost diameter of each shielder (15; 32; 34) and a position eccentric with respect to the axis of each roller (2), and a second light receiver (23) located at a position below the axis of each roller (2) and capable of receiving the light ray emitted from said second transmitter (21). An apparatus as claimed in Claim 2, wherein each shielder (32) is of a fan shape in cross section. An apparatus as claimed in Claim 2, wherein each shielder (15) is of a semicircular shape in cross section. An apparatus as claimed in any one of Claims 2-4, wherein each shielder is attached to a follower end of each roller. An apparatus as claimed in any one of claims 2-5, wherein each shielder (15; 32; 34) is an integral part of each roller (2). An apparatus as claimed in any one of Claims 2-5, wherein each shielder is provided separately from each roller. An apparatus as claimed in any one of Claims 2-7, wherein said light rays (A, B) are laser beams. An apparatus as claimed in any one of Claims 2-7, wherein said light rays are visible rays. An apparatus as claimed in any one of Claims 2-7, wherein said light rays are infrared rays. An apparatus as claimed in any one of Claims 2-10, wherein said first transmitter (20), said second transmitter (21), said first receiver (22) and said second receiver (23) are located in each of zones provided over a given length in the longitudinal direction of said kiln. An apparatus as claimed in any one of Claims 2-10, wherein said first (20) or second transmitter (21) and said first (22) or second receiver (23) are located on both ends of said kiln, as viewed in its longitudinal direction. An apparatus as claimed in any one of Claims 2-12, wherein said means for rotating said rollers in phase is a driving chain. An apparatus as claimed in Claim 13, wherein said driving chain is a double-driving chain comprising a first chain for driving every other one out of roller groups and a second chain for driving every another one. An apparatus for detecting roller breakdowns in a roller hearth kiln wherein a plurality of rollers are arranged side-by-side in the transport direction of said kiln and are rotated synchronously, characterized in that each said roller (2) carries a light shielder (15; 32; 34) and at least two light ray transmitter/receiver devices (20, 21/22, 23) are arranged in relation to said shielders so that in normal operation the light rays (A, B) are intermittently blocked and unblocked by the shielders (15; 32; 34) and, when any one shielder (15; 32; 34) ceases to rotate due to breakdown, at least one of the light rays (A, B) is continuously blocked.

Inventors: AOKI MICHIRO, AOKI, MICHIRO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1990
Main classification: F27B9
IPC codes: B65G43, C21D9, F27B9, F27D21