GUSTAVSSON, Lars, Børje (Violvegen 5, Årjäng, S-67231, SE)
ENGEN, Roy (Prost Blomsgt. 31B, Gjøvik, N-2819, NO)
ANDERSEN, Jens (Syrinveien 5, Drammen, N-3014, NO)
LARSSON, Kaj (Klangsveg 5, Grebbestad, S-45795, SE)
GUSTAVSSON, Lars, Børje (Violvegen 5, Årjäng, S-67231, SE)
ENGEN, Roy (Prost Blomsgt. 31B, Gjøvik, N-2819, NO)
ANDERSEN, Jens (Syrinveien 5, Drammen, N-3014, NO)
P a t e n t c l a i m s
1. A detector means for detecting at a position in a conveyor a jam situation relating to a sheet or board being conveyed on the conveyor, the conveyor comprising a frame carrying at least two rotatable, elongated rollers being spaced with longitudinal axis thereof in parallel and substantially perpendicular to the conveying direction, characterised in that said detector means includes a sensing lobe being arranged to be pivotable about a first end to first and second pivoting positions in said space between the rollers by its displacement through contact with a plate or sheet on the conveyor, such that a second end of the sensing lobe in the fist pivoting position protrudes into a first area for occupation by the plate or sheet and in the second pivoting position protrudes into a second area not including said area for occupation, an elongated shaft being rotatable about its longitudinal axis and being at a first end thereof rigidly attached to the first end of sensing lobe, thereby providing a pivoting axis for the pivotable sensing lobe, said pivoting axis being substantially parallel to the longitudinal axis of the rollers, a positioning means attached to the second end of the elongated shaft and being adapted to effect a rotation of the shaft so as to position the lobe in the first pivoting position when there is no board or sheet in the area for occupation displacing the lobe, a shaft supporting means being arranged between the sensing lobe and the positioning means and being adapted to be fixedly mounted to the frame for maintaining the shaft and lobe assembly positioned between the rollers and for maintaining the shaft in an area away from the area for occupation, and a position indicator means rigidly attached to the second end of the shaft to indicate said first and second pivoting positions of the sensing lobe.
2.
The detector means of claim 1, wherein the sensing lobe comprises an elongated member of a rigid material.
3. The detector means of claim 1 or 2, wherein the sensing lobe comprises an elongated member having a bend.
4.
The detector means of claim 2 or 3, wherein a bend is at about the mid point of the elongated member.
5.
The detector means of claim 3 or 4, wherein the bend exhibits a bend angle in a range from about five to about sixty degrees, preferably in a range from about five to about forty-five degrees, more preferably in a range from about seven to about fifteen degrees.
6.
The detector means of any one of the preceding claims, wherein the positioning means includes at least one of a weight, a magnet or a resilient element.
7.
The detector means of any one of the preceding claims, further including a sensor means adapted to be mounted stationary with respect to pivoting members of the detector means, said electrical sensor being adapted to observe the position indicator means and to output position state signals indicating said first and second pivoting positions.
8.
The detector means of claim 7, wherein the sensor means is an electrical sensor device comprising a magnetic, an optical, a capacitive, an inductive or a mechanical switch sensor.
9.
The detector means of claim 7 or 8, wherein the position indicator means comprises a magnetic, an optical, a capacitive, an inductive or a mechanical indicator device.
10.
The detector means of any one of claims 7, 8 and 9, further including a separator arranged between the flag device and the electrical sensor means.
11.
The detector means of any one of claims 7, 8, 9 and 10, further including a timer device having an input for receiving said position state signals indicating said first and second pivoting positions, said timer device being adapted to determine a first interval for the lobe being in the first pivoting position or a second interval for the lobe being in the second pivoting position, and an output means adapted to output a warning or alarm signal if the first interval exceeds a predetermined first threshold or the second interval exceeds a predetermined second threshold.
12.
A dryer in a production line for continuous production of said sheet or plate, said dryer including a plurality of said conveyors in respective tiers of a vertically tiered arrangement, and wherein at least two of said plurality of said conveyors comprises the detector means of any one of the preceding claims.
13.
The dryer of claim 12, further including a plurality of the detector means of any one of claims 1 - 11, in a spaced arrangement in each of said tiers comprising said at least two of said plurality of said conveyors.
14.
The dryer of claim 12 or 13, further including an operator console having a video display unit or data screen, being adapted receive said position signal, and to display by a first colour the first pivoting position and by a second colour the second pivoting position.
15. The dryer of claim 12 or 13, further including an operator console having a video display unit or data screen, being adapted receive said first or second intervals or said first or second thresholds, and to display by numbers a value representing any one of said first or second intervals or said first or second thresholds.
16.
The dryer of claim 14 or 15, wherein the operator console having a video display unit or data screen further being adapted to display said first and second pivoting positions, said first or second intervals or said first or second thresholds, in a structured arrangement corresponding to the tiered arrangement of the conveyors. |
Jam Detector for a Fibre Board or Gypsum Drywall Dryer
The present invention relates to an apparatus for production of sheet- or board like material, such as fibre boards or gypsum wallboards, and more particularly to a detector for detecting a jam occurring in a dryer included in a production line for the production of said sheet or board.
Fibre boards and drywalls are used in large quantities in the building industry, and are typically produced continuously in a production line which is fed with pulp or a slurry comprising fibres or gypsum containing a high percentage of water. In the production line the water is removed to achieve the product as a dry fibre board or gypsum drywall for its subsequent packing and shipping to a building site.
To remove the water, the production line includes a dryer, typically including a conveyor on which the sheets or boards are conveyed through the dryer, while hot air is circulated through the dryer. Thereby, excess moisture is removed from the sheet or board as it passes through the dryer.
A dryer for the manufacturing of a sheet or board of the aforementioned types typically includes several layers of conveyors, to provide the capacity needed for an efficient manufacturing with a dryer of a reasonable length. Still, a typical dryer for the manufacturing of a fibre board, the dryer having a total of 12 layers, may have a length of 60 meters or more.
To allow a good flow of hot air through the dryer, and to ensure stable operation at temperatures in a range from 150 0 C to more than 200 0 C, the conveyor in each layer of the dryer comprises a large number of rollers in a common plane. The rollers may be rotated by a common motor driven chain drive, and the sheets or boards are advanced resting on the rollers that are driven to rotate in the same direction.
In the early stages of the manufacturing line, at a point where the sheet or board is fed to the dryer, the sheet or board has still not cured to a point where it is solid and capable of withstanding substantial mechanical forces without disintegrating. On the contrary, when being input to dryer, the sheet or board is soft and fragile and may have a water content reaching as high as 80% by weight, and may easily disintegrate if subject to mechanical stress. A further complicating factor may occur if the sheet or board in the early stages of the manufacturing exhibits parts that are flawed, such as for example due
to air bubbles or uneven distribution of fibres or gypsum comprised in the sheet or board, the sheet or board could disintegrate or come apart while being conveyed in the dryer, hi a situation where a sheet or board, while being vulnerable in the early part of the dryer, disintegrates or comes apart, for the aforementioned or other reasons, the sheet or board may become j ammed in the dryer. Typically, the j amming of the sheet or board in the dryer, such as in the example mentioned above in a dryer having 12 layers on top of each other over a length of 60 metres or more, the jamming in one layer would often result in debris and material from a disintegrated sheet or board to fall down on or progress into adjacent layer, and will, eventually, cause a total jamming of the dryer, having the effect that the manufacturing line must be stopped for cleaning the dryer before the production line can be restarted. It is well known that jamming of a dryer in a production line for fibre boards (pulp based) may lead to a stop in the production for one week or more, when working full day and night shifts to restore the dryer back to normal operation.
Besides being caused by the disintegration or breakage of a sheet or board being conveyed to be dried in a dryer, jamming may also be caused by a failure of one or more of the conveyor rollers, or in a drive for the rollers.
U.S. patent No. 5,678,322 discloses a jam detector for a wood veneer dryer. The veneer dryer includes a dryer housing that has at least one conveyor for conveying veneer panels from a first end of the dryer towards a second end of the dryer. A laser apparatus directs a laser beam above the conveyor, and the laser apparatus generates a distance signal which is representative of the distance between the laser apparatus and an object intersecting the laser beam. Typically, the veneer panels establish an operating configuration wherein each panel layers substantially flush against the conveyor and the panels are thereby conveyed to the dryer. Even new panels can also establish a jam configuration, wherein plural panels are stacked. The laser apparatus is disposed such that the laser beam propagates from one end of the dryer housing to the other when the panels are in the operating configuration, while impinging on at least one panel when the panels are in the jammed configuration.
U.S. patent No. 5,371,583 discloses a roller breakage detector for roller hearth kilns for firing material while it is being carried and more specifically a system for detecting roller breakage or failure in a roller hearth kiln. When a roller or rollers therein fail or break down, the roller hearth kiln has some difficulty in smoothly carrying the material being treated, because the broken roller or rollers form or forms a barrier. It is then
required to detect such roller breakage promptly, to replace the broken rollers by new ones. In the kiln body of which an array of rollers is arranged in the lengthwise direction to fire material while it is being carried, a light projector located at a position below the axis of said roller array in the lengthwise direction for generating at least an optical signal in the lengthwise direction, and a light receptor located at a position below the axis of said roller array in the lengthwise direction for receiving the optical signal generated from said light projector. When the rollers rotate normally, the rays emitted by the projectors enter immediately these receptors, and the receptors output signals, indicating that the rollers rotate normally. When there is a roller breakage, the roller falls due to gravity and tilts down. Then, a part of the rays generated by the projectors is cut off by the broken roller piece, which ensures to detect the roller breakage, because the rays do not enter the associated receptor.
The present applicant has experienced that jam detectors of prior art for a fibre board dryer are unreliable, as the fibre boards may be properly conveyed to the dryer when there is no jam situation present and jam alarms are still generated due to bending or buckling of the sheet or board being conveyed, due to dust and particles being carried by the air flow in the dryer, or due to other factors, such as temperature differences or even misalignment or movements of parts of the conveyor system or other parts comprising the dryer that otherwise are not detrimental to the operation of the dryer.
Accordingly, there is a need for a jam detector for a dryer in a production line for a sheet or board, and specifically for a fibre board dryer, that will reliably detect a jam situation of the sheet or board in the dryer.
The present invention provides a detector means for detecting at a position in a conveyor a jam situation relating to a sheet or board being conveyed on the conveyor, the features of which being recited in the accompanying independent patent claim 1.
Further advantageous features of the detector means of the invention are recited in the accompanying dependent patent claims 2 through 11.
The present invention provides a dryer in a production line for continuous production of a sheet or plate, comprising a jam detector according to the features recited in the accompanying patent claim 12.
Further advantageous features of the dryer of the invention are recited in the accompanying dependent patent claims 13 through 16.
The present invention will now be described by way of example and with reference to the accompanying drawings, wherein:
Figure 1 illustrates in a perspective view a production line for continuous production of a fibre board.
Figure 2 illustrates by a perspective view of a multi-layer dryer the principles of the dryer illustrated in the production line of Figure 1.
Figure 3 illustrates in a partial side view a multi-layer dryer including a first set of jam detectors according to the present invention.
Figure 4 is a detailed, enlarged part of the illustration provided in Figure 3 of a set of detectors according to the present invention.
Figures 5 a, b, and c illustrate, in a perspective view, a side view and a top view, respectively, a conveyor jam situation detector according to the present invention.
Figures 6 a, b, c, and d illustrate, in a perspective, view, a side view, a top view and an end view, details of a shaft having a sensing lobe in a conveyor jam situation detector according to the invention.
Figure 7 is a schematic drawing illustrating a further embodiment of the present invention.
Figure 8 illustrates a display arrangement for an embodiment of the present invention.
With reference to Figure 1, a typical production line for manufacturing of a sheet or board, such as a fibre board or a drywall, will be explained. The production line illustrated in Figure 1 is specifically adapted for manufacturing of a fibre board type sheet or board. The production line comprises generally six sections, in Figure 1 labelled A through F. In section A, a slurry is deposited in a slurry depositor 100 onto a moving web 110. The moving web allows water to drain through, while maintaining fibres 5 in the slurry on its upper surface. By the moving web 110, the fibres 5 deposited
on the web are conveyed towards, and fed into, a set of oppositely arranged pairs of rollers 120 that compress the fibres conveyed from the movable web 110, thus further reducing the amount of water held by the fibre mass 5. By the forces applied to the fibre mass 5 by the set of roller pairs 120, the sheet or board 10 is formed. The roller pairs
5 120 are located in section B of the manufacturing line. In section C, the sheet or board exiting from the roller pairs 120 is transported further on a first belt type conveyor 130 that is co-located with a cutter apparatus. The cutter apparatus in section C cuts the sheet or board exiting from section B into conveniently sized sheets or boards that are conveyed further into section D of the production line. In section D of the production io line, a conveyor/distributor 140, adapted to convey the sheet or board section forwarded from the cutter in section C in a direction of the production line as well as in a vertical direction, so as to feed the sheet or board section 10 into a layer of the dryer 200, labelled section E of the production line, which is free to receive a sheet or board section. The dryer 200, which typically may be 60 meters or more of length, comprises i 5 a number of roller conveyors, layered one above the other, to form a multi-tired dryer section. At section F of the production line, the sheet or board section 10 exits in a dried or cured condition onto a collector and conveyor 150, adapted to convey the sheet or board in a direction along the production line as well as in a vertical direction, so as to collect a sheet or board that exits at any layer of the dryer of section E.
20
At section D of the production line, the sheet or board section 10 has a high moisture content, and, in particular with respect to a fibre board or a gypsum drywall, has not cured to a point where it can sustain mechanical impacts without falling apart, thus being very fragile at the point where it enters the dryer of section E of the production 25 line.
It should be noted, that the production line that is schematically illustrated in Figure 1 is not drawn to scale, and that section E of the production line typically is substantially longer than other sections of the production line.
3Q
After having been fed into the dryer 200, the freshly made sheet or board sections 10 remain fragile in a substantial part of the dryer, as it is conveyed through the dryer by the roller conveyors of the dryer.
3 5 Reference is now made to Figure 2, indicating the principles of the dryer 200, provided with a jam detector arrangement 300 according to the present invention. The dryer 200 comprises a dryer housing 210 having therein a large number of rollers 220 arranged
side by side and in layers, thereby forming layers, or tires, of roller conveyors. Typically, a dryer 200 in a dryer section E of a sheet or board production line may include as many as 12 layers of roller conveyors. In the dryer, air of temperatures in the range from about 16O 0 C to about 24O 0 C is circulated through the dryer, and also between the rollers of the dryer, to remove moisture from the sheet or board sections 10 and/or to achieve any curing required for the board to have obtained the necessary mechanical strength before it exits the dryer into section F of the production line. Last, the board or sheet section 10 is gradually dried, or cured, as it is conveyed through the drawer, implying that there is a critical first portion of the dryer towards section D of the production line where a disintegration of the freshly made sheet or board section 10 is most likely to occur. Accordingly, it has been found beneficial to provide the dryer with a jam detector in a part of the dryer that is towards section D of the production line.
Reference is now made to Figure 3, which shows in a partial side view a sheet or board dryer 200 having six layers of conveyor rollers, and being provided with two arrays 300 of jam detectors 310,320 according to the invention. In Figure 3, a situation is illustrated at a point in time where the conveyor 220 of the lowest layer conveys a sheet or board section 10 as it passes a first array 300 of jam detectors as well as a second array 300' of jam detectors according to the invention. This, second lowermost layer on roller conveyors 220 of this example, has just received a sheet or board section 10, which has entered the dryer 200 to an extent where it is located in an area of the first array 300 of jam detectors according to the invention, while it has not yet progressed to a point where it is in an area of the second array 300' of jam detectors according to the invention. The third lowermost layer of roller conveyors 220 is, in the situation illustrated in Figure 3, presently not loaded with a sheet or board section 10 in any of the areas of the first array 300 or the second array 300' of jam detectors according to the invention. With regard to the upper three layers of the example of a dryer 200 illustrated in Figure 3, the situation should be readily understood from the explanations given with respect to the situation depicted and explained for the three lowermost layers. Although arrays 300,300' of jam detectors 310,320, or further arrays thereof, are illustrated in the example shown in Figure 3, individual jam detectors 310,320 may be arranged at the various layers as needed to provide the desired detection of a jam situation in the dryer 200.
Reference is now made to Figure 4 for a more detailed explanation of the jam detector of the invention. Figure 4 is a partial view of the view shown in Figure 3, showing a first layer of rollers 220 constituting a first roller conveyor, and a second set of rollers
220' constituting a second roller conveyor, the second roller conveyor being situated immediately above the first roller conveyor. A plate or sheet 10 is being transported on the first roller conveyor, while the second roller convenor does not convey a sheet or plate in the area shown in the partial view of Figure 4. The jam detector array 300 illustrated in Figure 4 includes a first jam detector 310a,320a arranged in conjunction with a pair of rollers of the first roller conveyor 220a, and a second jam detector 310b,320b arranged in conjunction with a pair of rollers of the second roller conveyor 220b. The jam detector 310b,320b as illustrated in the accompanying drawings generally comprises a presence detector 310, which can be placed in different states depending on the presence or absence of a sheet or board 10 in a detection area of the jam detector. To that end, the detector 310 is provided with a position state indicator means providing means for observation of the jam detector state in order to determine the existence of a jam situation. A sensor means 320 is positioned in conjunction with the jam detector 310 so as to read the position state indicator for allowing a remote observation of the state of the jam detector 310. In the situation illustrated in Figure 4, the second, upper conveyor 220b does not convey a sheet or plate 10 in a position along the dryer 200 where the array 300 is located, thus putting the detector 310b in a state for no sheet or board 10 in its area of detection, in contrast to the situation for the first, lower roller conveyor 220a, on which a sheet or board 10 is being conveyed in the detection area of the detector 310a, which, thereby, is placed in a state for a sheet or board 10 being located in its detection area.
With reference to Figures 5a, 5b, and 5c, the jam detector 310 will be explained in more detail.
The exemplary embodiment of a jam detector according to the invention as illustrated in Figures 5a, 5b, and 5c, comprises an elongated shaft 312 carried by a support 313. Bearings 314 and 315 allow this shaft to be rotatable about its longitudinal axis. At one end of the shaft, which preferably is proximal to the bearing 315, a sensing lobe is rigidly attached to the shaft, such that the shaft 312 provides a pivoting axis for this sensing lobe 311. Preferably an end area of the shaft, being opposite to the end at which the sensing lobe 311 is attached, is arranged a positioning means 316, for maintaining the sensing lobe 311 in a first pivoting position at the time when no object, such as a sheet or plate 10, is present to in the detection area displace the sensing lobe 311. Preferably, the positioning means 316 is embodied by a weight fixed to the shaft 312 and positioned offset from the longitudinal axis of the shaft 312 and to the opposite side of the longitudinal axis of the shaft 312 with respect to the sensing lobe 311. Thus, by
the bearings 314 and 315 allowing the shaft 312 to move freely in a rotational direction about its longitudinal axis, gravity will bring the weight leaver 316 to rest in a position below the longitudinal axis of the shaft 312, while the sensing lobe 311 is brought into the first pivoting position, located above the longitudinal axis of the shaft 312.
In a further embodiment of the invention, a spring being attached at one end to the shaft 312 and at the other end to the support 313 or some other element that is substantially rigidly attached to the support 313, is appropriately arranged so as to bring the sensing lobe 311 into the first pivoting position as illustrated in Figure 5a, when no object, such as the sheet or plate 10, is present to displace the sensing lobe from the first pivoting position. Such a spring to take the place of, or to operate in combination with a weight to form the positioning means 316, is not shown in the accompanying drawings. The positioning means 316 may, however, be attached to the pivoting shaft 312 at any point where it does not interfere with the conveyor rollers 220, although, in a dryer for manufacturing of fibre board which due to high temperatures and rapidly moving air with a high content of moisture and particles, an advantageous solution is to employ a weight lever for the position means 316, attached to a portion of the shaft 312 that is allowed to extend to the exterior of the dryer, such as by passing the shaft through a suitable hole in a wall of the dryer 200.
In one embodiment of the present invention, the position state indicator means 317, being rigidly attached to an end of the shaft 312 to be located exterior to the housing of the dryer 200, comprises an indicator means adapted to allow remote observation of the pivoting positions of the sensing lobe, such as by including a magnetic, an optical, a capacitive, an inductive or a mechanical indicator device. Thus, the position state indicator means may be observed by a corresponding transducer, such as the sensor means 320 illustrated in Figures 3 and 4, being capable of detecting any of the aforementioned types of indicator device. As an example, the position indicator means 317 could be a magnet, while the sensor means 320 could be a reed-switch or an hall element enabled to detect the magnet when it is brought into proximity of the sensor means 320. Having suggested the position indicator means to be an optical, capacitive, inductive or mechanical indicator device, a person skilled in the art would be capable of identifying the electrical sensor means that is most properly suited to cooperate with and detect the position indicator means 317. It should be noted that the position indicator means 317 could be attached to the shaft 312 in different ways from the embodiment illustrated in Figures 5 a, b and c, to allow for detection of at least the first and second pivoting positions of the sensing lobe.
As indicated above, the detector means 310 of the present invention, preferably, is to be located within the dryer 200, between a pair of rollers 220 of a roller conveyor, with one end of the shaft 312, being the end of the shaft 312 opposite to the end to which the sensing lobe 311 is attached, exiting through a hole in a side wall of the dryer 200. In an embodiment of the dryer 200 incorporating the present invention, a further separating element 210 is arranged between the position indicator means 317 and the sensor means 320, as illustrated schematically in Figure 7. The element 210 provided between the position indicator means and the sensor means allows for a separation of the sensor means from the environment experienced in the dryer 200, thus further improving the reliability of a system based on remote observation by use of an electronic sensor means 320, which itself thereby is not being subject to the high temperatures, high humidity, and dust and particles of the interior of the dryer 200. In an advantageous embodiment of the dryer 200 incorporating the present invention, the separator 210 is provided by a transparent material, such as glass or Plexiglas, to allow visual inspection and simple testing of the detector means 310 of the invention from outside of the dryer 200, while the dryer 200 and the production line are in normal operation.
With further reference to Figure 7, a remote observation 400 and alarm generating 430 means are illustrated, being in communication with the sensor means 320 for providing an operator's interface on a visual display unit (VDU) or data screen 420, to indicate at a remote position the position states of a plurality of detector means 310 according to the invention, to indicate to the operator normal operation of the dryer or an abnormal state caused by a jam in the dryer. The example illustrated in Figure 8 represents a user interface 421 allowing a remotely positioned operator to observe two arrays of detector means 310 according to the invention, located at different positions along the dryer, where each array includes 12 jam detectors of the present invention. When the sheet or board 10 is being conveyed past the detector means 310 of the invention, the sensing lobe is displaced by the sheet or board 10 into the second pivoting position, which is indicated on the operator's VDU interface 421 (fig. 8) by a bright circle, while a dark circle indicates to the operator that the sensing lobe is in the first pivoting position as no sheet or board 10, or part thereof, is present in the detection area of the sensing lobe. A control unit receiving 410 a signal from the sensor means 320 may include at least a first counter, or timer, adapted to be reset when a signal indicating the sensing lobe in the first position, while the counter is operating in a timer mode to count seconds to indicate the duration of a period during which the sensing lobe is in the second pivoting position. The output of the timer (counter) is fed to a comparator, wherein the timer
(counter) value is compared with a predetermined value that represents the time (count) would take for a sheet or board 10 to pass the detector means of the invention while being conveyed at a normal conveying speed. Accordingly, if the period (count) determined while the sensing lobe is in the second pivoting position exceeds the predetermined limit, the comparator will output a signal to indicate to the operator that the sheet or plate 10 is not being conveyed at a normal speed past the detector means of the invention, which typically is an indication of a jam situation developing or already in existence in the dryer 200, or, possibly, a situation developing or existing in an area at the entrance or the exit of the dryer 200 that has an effect on the conveying through the dryer.
In a further embodiment of the jam detector according to the invention, the timer/counter receiving a signal from the sensor means 320 is adapted to determine a period during which the sensing lobe is in the first pivoting position, to indicate a gap between sheets or boards 10 being conveyed by a roller conveyor 220 in the dryer. Thus, by detecting a gap being too long, or possibly too short, between two sheets or boards 10, an abnormal situation in the conveyance of a board or sheet 10 past the detector, or possibly the existence of debris or other material from a board or sheet that has disintegrated in the corresponding or a different layer of the dryer, may be detected, by comparing the period during which the sensing lobe is indicated in the first pivoting position with an upper, predetermined limit on the duration of the allowable time for the sensing lobe to remain in the first pivoting position. A further development may include a predetermined, lower (minimum) value for the sensing lobe indicated to be in the first pivoting position.
In a further embodiment, the present invention may include the observation of a sensor signal indicating the sensing lobe in the second pivoting position, and to compare a period determined by the timer/counter during which the sensing lobe is in the second pivoting position, and compare the period with a predetermined, minimum value, and to provide a warning or alarm by an indicator 430 to the operator if the period during which the sensor indicates that the sensing lobe is in the second pivoting position is too short. Thus, the detector of the invention may indicate to the operator that the sheet or board 10 being conveyed past the detector means of the invention has broken into smaller pieces, or even that the cutter in section C of the production line has cut the sheet or board 10 to a size that is different from the intended size, or even that there is some other problem related to the operation of the conveyor 220 of the layer in which the respective detector means of the invention is located.
Furthermore, also with reference to Figure 8, a control unit 410 arranged to receive signals from electrical sensor means 320 of a detector means according to the invention includes a record keeper to keep record of the number of jam situations observed by the detector means of the invention, and a means to display 421 to the operator the time calculated to be the appropriate duration of a period for a sheet or board 10 to pass the detector means in the dryer, and one or more alarm limits to be applied in comparing the timer/counter output for detecting a jam situation, or other situation that is considered not normal for the process of conveying the sheet or board 10 through the dryer 200.
With reference to Figure 6, a more detailed description will be provided of a shaft 312 and sensing lobe 311 assembly in a further embodiment of the present invention. Of the total length of shaft 312, at a first end at which the sensing lobe 311 is to be attached, about 5% on one end is maintained free to allow engagement with a first bearing 315 to support the shaft 312. Immediately proximal to the free part, the sensing lobe 311 is attached rigidly to the shaft. The sensing lobe, typically an elongated plate element, advantageously of a rectangular shape, is at one end rigidly attached to the shaft 312, and about at half of its length provided with a bend in a direction that will correspond to the direction of conveyance of a sheet or board 10 when the detector is located in the dryer, hi an advantageous embodiment of the invention the bend is such that the two parts, on each side of the bend, are at an angle about the bend of about 170° with respect to each other. Other dimensions, and also the bend angle, may be adapted to suit the type of sheet or board 10 product that is being manufactured, in order to ensure proper operation of the detector means of the invention, while not interfering with the product that is being made in the production line. Thus, the dimensions and angles indicated here have proved to provide good results, while other advantageous dimensions and bend angles are recited in the accompanying patent claims.
Next Patent: IMPROVED SPREADS