METHOD AND APPARATUS FOR THE POSITIONING OF SLABS

Abstract: This invention relates to a method of and apparatus for the positioning of thick slabs (2) to be introduced into a furnace, particularly into a walking-beam furnace, said positioning being effected with the aid of optical means (5, 9, 10) and electronic means (11, 12). By this method, at each lateral region opposite the furnace mouth (3), onto the upper surface of a slab (2) and at the region of its end faces (102, 102′), there are projected at least two blades of light (6, 7, 8) of a given length, which are normal to the direction of entrance and advance into the furnace and parallel to each other, the ends of which are perfectly aligned on a straight line which is parallel to the direction of entrance and advance into the furnace, said blades (6, 7, 8) producing parallel lines of light (106, 107, 108) on said surface of the slab (2), said lines being interrupted at the end edges (102, 102′) of said slab. The deceleration of the slab transporting movement, and the stoppage thereof, is determined with the aid of electronic means (11, 12) as a function of the length of said lines of light (106, 107, 108).

Description: This invention relates to a method for the positioning of slabs to be introduced into a furnace, particularly into a walking-beam furnace, with the aid of optical and electronic means. According to this method, at least one slab is fed along a virtual slab-feeding horizontal plane, orthogonally to the direction of entrance into, and advance through the furnace, in front of the furnace mouth, and in the position in which it will be introduced into the furnace. In the region opposite the furnace-mouth, the invention provides also an apparatus for carrying out this method, consisting of a horizontal path formed by powered rollers, or the like, for feeding the slabs in front of the furnace-mouth, orthogonally to the entrance direction into, and advance through the furnace, and consisting of a plurality of light sources which are directed onto the slabs in the region opposite the furnace-mouth, and of telecameras directed on the region opposite the furnace mouth and connected to display monitors, and of a microprocessor connected to the monitors. Usually, the slabs are fed orthogonally to the direction of entrance into, and advance through the furnace, in front of the mouth of a furnace, particularly of a walking-beam furnace, and in the position in which they will be introduced into the furnace, with the aid of a roller-path, or the like, and the slabs are then introduced into the furnace by means of suitable furnace-feeding devices, in the same position as on the roller path. In order to avoid any accident while the slabs are getting through the furnace, the slabs have to be introduced into the furnace in the best possible correct position, i.e., with their longitudinal axes arranged perpendicular to the direction of movement through the furnace, which is generally parallel to the longitudinal axis of the furnace, and with their intermediate transverse axes arranged parallel to the longitudinal axis of the furnace, i.e., to the direction of entrance into, and advance through the furnace. Moreover, the slabs must be exactly centered with respect to the furnace-mouth. If it is a matter of short slabs which can be introduced two by two into the furnace, the longitudinal axes of these short slabs must coincide. Therefore, to introduce slabs into a furnace, a positioning device is required for controlling the roller-path so as to ensure a correct positioning of a slab relative to the furnace mouth. In a known slab-positioning method, laser beams incident on the slab endwalls are used, and the reflected image of said beams is detected by optical and electronic means, for example, by telecameras associated with display monitors and with an electronic processor. According to this known method, in order to determine the correct slab-centered position relative to the furnace-mouth, the angle of the laser beam reflection on the end face of a slab is measured, which varies depending upon the different positions on the roller-path, the like. By this known method, the disadvantage is eliminated of the slabs slipping on the rollers, which is found in the methods used heretofore. However, since the end face of a slab, against which the laser beam is projected, often is considerably irregular, in this known method there is still the drawback that the laser beam may often impinge against ridges or valleys on or in the generally rough end face of a slab, thus causing a displacement in the actual position of the slab. Moreover, by this method it is not possible to determine any error in the orientation of a slab with respect to the direction of entrance into, and advance through the furnace. The object of the present invention is to provide a slab-positioning method and apparatus of the type as disclosed at the outset, by which the aforementioned disadvantages will be eliminated, so that a correct and exact positioning of the slabs relative to the furnace-mouth is made possible, by using comparatively simple means of a low-cost construction. The invention solves this problem by a method according to the second part of claim 1. If it is the matter of two short slabs, that is, of two slabs whose length is at the most shorter than one-half of the width of the furnace-mouth, these short slabs are fed in pairs into the position in which they will be introduced into the furnace, according to what is contemplated in the characterizing part of the dependent claim 2. By the method according to the invention, it is also possible to check and correct the inclination of the slabs with respect to the slab-feeding direction, according to the teaching of the dependent claim 5. A particular embodiment of an apparatus according to the invention, for carrying the said method, is made according to the teaching of the dependent claim 9. The invention thus affords the advantage of rendering an automatic, exact positioning of the slabs possible, independently from any slab distortion, not only in connection with the centering of the slabs in respect of the furnace-mouth, but also in connection with their orientation in respect of the direction of entrance into, and advance through the furnace, even in the case of two short slabs being simultaneously introduced into the furnace. Other features further improving the slab-positioning method and apparatus as disclosed above, also form the object of the invention, and are the subject of the dependent claims. The particular features of the invention, and the advantages arising therefrom, will appear more in detail from the description of one preferred embodiment thereof, which is shown by way of a non-limiting example in the accompanying drawings, in which: Figure 1 is a side view of an apparatus according to the invention. Figures 2 and 3 are two top views of the apparatus according to the invention, respectively with a long slab and two short slabs. Figure 4 is a block diagram of the electronic circuit for the apparatus according to the invention. Figures 5 and 6 show the images appearing on the monitor, which correspond to two different orientations of a slab. In the apparatus described hereinbelow, it is assumed that the longitudinal axis of the furnace coincides with the direction of entrance into, and advance through the furnace. Figure 1 shows an apparatus according to the invention, comprising a powered roller path 1 for feeding the slabs 2, the said roller-path being arranged normally to the longitudinal axis of the furnace, in front of the furnace-mouth 3. On the side of the roller-path 2 that faces away from the furnace-mouth 3, an upright structure 4 fixedly supports two sources of light designated by the reference numeral 5, which are each arranged opposite a lateral region of the furnace-mouth 3, and are directed against a slab 2 disposed on the roller-path 1. The beams from the sources of light 5 are converted with the aid of suitable optical devices, into three beams of light 6, 7, 8, in form of thin planes, so-called blades of light, disposed on three planes which are inclined to the horizontal plane, are so inclined to each other that their mutual intersection point coincides with the light sources 5, while at least two or three parallel lines of light 106, 107, 108 are projected on the slab 2. The light sources 5, moreover, are oriented so that the lines of light 106, 107, 108 created on the slab are normal to the direction of entrance and advance into the furnace, while their edges are perfectly aligned on a straight line which is parallel to the longitudinal axis of the furnace. On the side of the roller-path away from the sources of light 5 and above the top side of the furnace-mouth, opposite each lateral region, there is arranged a telecamera 9. Each telecamera 9 is directed towards the roller-path 1. The total field of vision of said telecameras 9, preferably, covers the entire stretch of roller-path 1 that is in front of the furnace-mouth 3. This arrangement is clearly apparent also from Figs. 2 and 3. As clearly shown in Fig. 4, each telecamera 9 is connected first to a display monitor 10 which, in turn, is connected to a microprocessor 11. Said microprocessor, moreover, is connected to a programmable-logic control unit 12 which manages the handling of slabs. The microprocessor 11 has an outlet 111 to control the conveying speed of the powered roller-path 1. The image which is projected onto the slabs 2 is picked up by the telecameras 9 and is displayed on the monitors 10. Fig. 5 shows the image which is obtained when a slab 2 is oriented correctly with respect to the longitudinal axis of the furnace. In this instance, the end face 102 of the slab is perfectly aligned with the longitudinal axis of the furnace. The monitor 10, therefore, will show the three lines of light 106, 107, 108 being projected on the slab as spaced by a vertical offset from three associated lines corresponding to three reference lines or projections of the blades of light 6, 7, 8 onto the rollers adjacent the end face 102. The spots of spacing or offset are disposed, in this instance, on a straight line which is parallel to the longitudinal axis of the furnace, while the length of the lines of light 106, 107, 108 from their ends on the slab to the spots of offset at the edge of the end face 102 is identical for all the lines. By virtue of the pair of reference borders 14 and 14′ which, in this instance, are in register each with a sidewall of the furnace-mouth 3, on the basis of the length of these lines of light the distances A and B of the end faces 102 and 102′ of a slab from the respective sidewall of the furnace mouth 3 can be determined, and, therefore, the automatic centering of the slab 2 with respect to the furnace-mouth 3 can be effected, by suitably controlling the speed of the roller-path 1. The deceleration of the roller-path 1 is controlled by the microprocessor 11 connected to the monitor 10 depending upon the difference of said two distances A and B of the respective end faces 102 and 102′ of a slab 2 from the corresponding sidewalls of the furnace-mouth 3 registering with the reference border 14 and 14′ whereby the deceleration is continuous and the slab 2 is stopped only when the distance A is identical to the distance B, i.e. when their difference is zero. In this instance, it is to be noted that the microprocessor will not initiate the control operation until the end face 102′, that is the rear wall with respect to the feeding direction of the slab 2, has come into the reach of the blades of light 6, 7, 8, i.e. until it has overstepped the reference border 14′ associated therewith, since only in this circumstance a definite value greater than zero exists for the distance B and the difference between the two distances A and B can be determined. Fig. 3 shows the apparatus according to the invention in case of two shorter slabs 2, 2′ to be introduced into the furnace simultaneously. In this instance, the distances A′ and B′ must be calculated previously, on the basis of the known lengths of the slabs 2, 2′. When the first slab, for example the slab 2, comes into the reach of the blades of light 6, 7, 8 in register with the sidewall of the furnace-mouth 3 associated therewith, the microprocessor commands the deceleration of the rollers, using as a reference parameter the difference between the measured value A and calculated value A′ transmitted automatically by the control unit 12 to the microprocessor 11 or entered manually by the operator, and stopping the slab 2 when the two values are identical, i.e. when their difference is zero. The deceleration and stoppage command for the second slab 2′ is initiated when the length of the lines 106, 107, 108 begins decreasing, since only then the slab 2′ has overstepped the reference border 14′ and its deceleration is similarly controlled depending upon the difference between the calculated distance and the measured distance, to come to a stop when such a difference is zero. Finally, as shown in Fig. 6, the method according to the invention may be used as well to determine the orientation of a slab with respect to the longitudinal axis of the furnace. In the case of Fig. 6, we have shown the end face of a slab 2 the longitudinal axis of which is not perfectly normal to the longitudinal axis of the furnace. In this circumstance, the end face 102 of the slab 2 is also inclined with respect to the longitudinal axis of the furnace, whereby the lines of light 106, 107, 108 have different lengths and show offset sections on a straight line 15 which is similarly inclined with respect to the longitudinal axis of the furnace. Therefore, by virtue of the microprocessor 11 connected to the monitor 10, it is possible to determine the angle of inclination and control mechanical orientation means (not shown) and/or a warning device for the personnel intrusted with the manual correction. The use of the monitors 10, and the fact that the total field of vision of the telecameras 9 covers the entire region in front of the furnace-mouth 3, enable additionally a direct visual check of said region by the personnel on duty. In all the apparatuses according to the invention, the roller-path may be replaced with any other equivalent conveyor means.

Claims: A method for the positioning of slabs to be introduced into a furnace, particularly into a walking-beam furnace, with the aid of optical means (5, 9, 10) and electronic means (11, 12), according to which method at least one slab (2) is fed along a virtual slab-feeding horizontal plane, orthogonally to the direction of entrance into, and advance through the furnace, in front of the furnace-mouth (3), and into the position in which it will be introduced into the furnace, characterized in that in front of each side edge of the furnace-mouth (3) at least two plane-like beams of light, i.e. light curtains (6, 7, 8), which are oriented in the feeding direction of the slab (2), and have a same origin, are projected on the said virtual slab-feeding plane (1), the said light curtains being angularly offset from each other around a horizontal axis coinciding with the said origin, or being parallel to each other, and the said light curtains producing on the said virtual slab-feeding plane (1), at the path of slab (2), two respective lines of light of a predetermined same length, which are directed parallel to each other and to the feeding direction of slab (2), with the distance of said lines of light from each other being shorter than the width of slab (2), and with their ends being mutually in line, orthogonally to the feeding direction of slab (2), the ends of said lines of light which are turned toward a virtual central vertical plane of the furnace-mouth (3) being at a sensible distance from this vertical plane, so that the actual value of the distance (A, B) between each end face (102, 102') of slab (2) and the respective side edge of the furnace-mouth (3) (the so-called measured distance) is measured and based on the length of the strokes of the lines of light (106, 107, 108), which are produced on the upper surface of slab (2) at its arrival in front of the furnace-mouth (3), the deceleration of slab (2) being commanded and based on the difference between the actual value of the distance (A) (measured distance) of the one end face (102) of slab (2) from the respective side edge of the furnace-mouth (3), and the actual value of the distance (B) (measured distance) of the other end face (102') of slab (2) from the respective side edge of the furnace-mouth, and the stopping of the slab being commanded when the said difference corresponds to a predetermined value, which is preferably equal to zero. The method according to claim 1, characterized in that the slabs (2, 2') (the so-called short slabs), whose length is at the most shorter than one-half of the width of the furnace-mouth (3), are fed in pairs in front of the furnace-mouth (3), into the position in which they will be simultaneously introduced into the furnace, and are decelerated and stopped independently from each other, the deceleration of the first slab (2), by taking into account the feeding direction thereof, being commanded depending upon the difference between the measured distance (A) of its fore end face from the respective edge of the furnace-mouth (3), and the nominal value of the said distance (A) at the position in which the first slab (2) will be introduced into the furnace, which value is calculated and based on the known length of the two slabs (2, 2') and the known width of the furnace-mouth (3), the stopping of the said first slab (2) being commanded when the said difference corresponds to zero, while the deceleration of the second slab (2') is commanded depending upon the difference between the measured distance (B) of this second slab rear end face (102') from the respective side edge of the furnace-mouth (3), and the nominal value of said distance (B) which is calculated and based on the known length of slabs (2, 2') and the known width of the furnace-mouth (3), the stopping of the said second slab (2') being commanded when the said difference corresponds to zero, and the deceleration command for the said second slab (2') being emitted when the length of the strokes of the lines of light (106, 107, 108), which are produced on the second slab upper surface at its arrival in front of the furnace-mouth (3), diminishes as the second slab (2') is being gradually advanced to the position in which it will be introduced into the furnace. The method according to claim 1 or claim 2, characterized in that on the virtual slab-feeding horizontal plane fixed, ideal reference lines (14, 14') are provided, which are orthogonal to the lines of light produced thereon, and define the width of the furnace-mouth (3) on the said virtual slab-feeding plane, and by the said fixed, ideal reference lines the actual value being measured of the distance (A, B) (measured distance) of each end face (102, 102') of slab (2) from the respective side edge of the furnace-mouth (3), by subtracting the length of the strokes of the lines of light (106, 107, 108), which are produced on the upper surface of slab (2) at its arrival in front of the furnace-mouth (3), from the length value of the lines of light produced on the virtual slab-feeding plane, between the intersection point with the respective ideal reference line (14, 14'), and the end of said line turned toward the virtual central vertical plane of the furnace-mouth (3). The method according to claim 3, characterized in that the reference lines (14, 14') coincide with the side edges of the furnace-mouth (3). The method according to any of the preceding claims, characterized in that the inclination of slab (2) relative to the direction of entrance into, and advance through the furnace, is indicated by the strokes of the lines of light (106, 107, 108), which are produced on the slab, and are of different lengths, the intersection points of the strokes of the lines of light (106, 107, 108) with the upper edges of the slab end faces (102, 102') being disposed on a straight line (15) having the same inclination as the slab end faces (102, 102'), relative to the direction of entrance into, and advance through the furnace, while the ends of said strokes of the lines of light (106, 107, 108), on the upper surface of slab (2), which are turned toward the virtual central vertical plane of the furnace-mouth (3), are in-line with each other always on a straight line which is parallel to the direction of entrance into, and advance through the furnace, so that the inclination of slab (2) is determined by mutually comparing the lengths of the individual strokes of the lines of light (106, 107, 108), which are produced on the upper surface of at least one end of slab (2), orienting means being provided for angularly shifting a slab (2) in the virtual slab-feeding plane (1), and being actuated when from the said comparison it appears that the said strokes of the lines of light (106, 107, 108) are of a length which is different for each one of them. The method according to claim 5, characterized in that the means for orienting the slabs (2) relative to the direction of entrance into, and advance through the furnace, consists of an automatic device which is controlled either by a microprocessor (11) or manually. An apparatus for carrying out the method according to any of the preceding claims, which is provided with a horizontal path formed by powered rollers (1), or the like, for feeding slabs (2) to the furnace-mouth (3), the said roller-path (1) being arranged orthogonally to the direction of entrance into, and advance through the furnace, and which is provided in the region opposite the furnace-mouth (3), with a plurality of light sources (5) that are directed to the slabs (2, 2'), and is provided with telecameras (9) that are directed on the region opposite the furnace-mouth (3) and are connected to display monitors (10), and also with a microprocessor (11) connected to the monitors (10), characterized in that this apparatus is fitted with at least two light sources (5), which are arranged on that side of the roller-path (1) which is opposite to the furnace-mouth (3), respectively in front of one side edge of the furnace-mouth (3), each of the said light sources projecting on the roller-path (1) at least two light curtains (6, 7, 8), which are oriented in the feeding direction of slabs (2, 2'), and this apparatus is also fitted with at least two telecameras (9) that are directed on the roller-path (1), and are disposed over the furnace-mouth (3), the said telecameras being each associated with one of the sides of the furnace-mouth (3), and being each connected to one display monitor (10), and the microprocessor (11) being connected both to the monitors (10) and to an electronic, programmable-logic control device (12) for the generation of control signals to the roller-path (1). The apparatus according to claim 7, characterized in that the light sources consist of light sources (5) fitted with additional optical devices for producing light curtains (6, 7, 8). The apparatus according to claim 7 or claim 8, characterized in that the total field of vision of the two telecameras (9) comprises the entire region opposite the furnace-mouth (3).

Inventors: FABBRINI, ALESSANDRO, MEINI, BRUNO, SCARSI, GIOVANNI
Applicants: IRITECNA SOCIETA PER L'IMPIANTISTICA INDUSTRIALE E L'ASSETTO DEL TERRITORIO PER AZIONI
Application year: 1989
Main classification: G01B11
IPC codes: F27B9, F27D21, F27D3, F27D19, G01B11, C21D9