METHOD FOR GUIDING SAW BLADES

Abstract: Circular saws (Fig 1), band saws (Fig. 2) or frame saws (Fig. 3) are intended for sawing straight as well as curved timber with knots and other irregularities which tend to direct the saw blade so that the kerf deviates from the desired kerf. It is known to design saw blades as a pack of at least two blades close to each other (1, 2). According to the invention the two saw blades are driven with intentionally variable relative speeds, each of them having their row of teeth (3, 4) which cannot interfere with the other row. Deviations from a wanted kerf are indicated by means of the deflections of the saw blade pack when it goes through the object to be sawn. The deviation controls the relative speeds of the saw blade halves. The saw blade which at a certain moment goes faster cuts a void towards which the pack is forced by the pressure from the teeth of the other saw blade. The method can be used on one hand to guide the saw to produce a straight kerf, on the other hand to guide the saw manually, and further to guide the saw according to a program for example to obtain planks with constant thickness from curved logs and also for joineries. It is also possible to produce chips with long fibres cheaper for fibreboard production.

Description: Method for guiding sat, blades. This invention relates to a method for guiding saw blades wi h at least two rows of cutting teeth which work in the same kerf close to each other and where the saw is guided to move sideways in desired direction or to compensate for deviations from a straight line caused by knots or the like. When sawing especially timber it is an object to produce as little waste as possible in the form of sawdust to get straight beams and planks from straight logs, and to obtain as many not necessarily plane planks as possible from curved logs. The planks are made plain afterwards when stored. It is also desirable to get long chips suitable for the production of fibreboards. -When sawing straight kerfs with a common circular saw the teeth must be symmetrically set and ground and the saw blade must be thick and stable in order to cut straight kerfs. This, however, leads to waste in plenty. The same applies for any now existing band-saw blades which have to be wide, thick and firmly stretched. The method according to this invention can be applied to circular saws as well as to band saws and frame saws. It is known to reduce the waste in sawdust by cutting the kerf with at least two adjacent saw blades which are driven with approximately the same speed ancT each of which has one row of teeth. The method according to the invention is essentially characterized in that the relative speed of the two rows of cutting teeth in the direction of movement through the piece of material to be sawn is intentionally varied so that the faster row of teeth becomes less engaged and therefore will, be subject to smaller cutting forces, whereby the resultant of the side forces perpendicular to the cutting forces will be directed towards the faster row of teeth, which causes the saw to move in the direction of the faster row of teeth, alternatively the piece of material to be sawn will move towards the slower row of teeth. The method according to the invention is used to guide the cutting direction either to a straight kerf or to a kerf with a desired curve. The control of the shape of the kerf can be accomplished either by means of sensors indicating the deflection of the saw blade when it has passed the . material to be sawn, or manually, or according to a computer program. The computer can for a joiner's workshop be programmed for sawing a desired pattern. It then coordinates the direction of cutting with the movement of the piece of material on the table. The program can also be stored immediately before sawing with data automatically measured of the curving of the log. It then guides the log and the direction of the cut to give th largest possible quantity of planks with constant thickness. As the direction of the cut is automatically controlled by means of the relative cutting speed, the total thickness of the combined saw blades can be made much smaller than the thickness of a single saw blade, the stiffness of which must guarantee the straightness of the kerf. For band and frame saws not only the combined thickness of the blades but also the width can be reduced to what is necessary to withstand the forces on the saw teeth. The total forces will be less since less material is wasted and a smaller width of the blade usually decreases the forces of friction. Thi also reduces the total consumption of energy for .sawing. According to a suitable embodiment of the invention the at least two saw blades are given different frequencies of resonance in order to avoid that the discs start to vibrate. By giving them different resonance frequencies they will damp each other whereby the risk for self-oscillatio will be eliminated. When the stretching forces on a saw blade and the thickness of the blade are no longer the sole factors taken into account for cutting sawing kerfs of desired form the stretching forces can be decreased and the machinery can be designed with smaller dimensions. Low weight of saw bands and blades allows a quick change of the relative cutting speed of the blades and thus a faster sawing. The invention will now be described with reference to Figs. 1-9 in which Figs. 1, 2 and 3 show circular saws, band saws and frame saws, Figs. 4 and 5 show different types of saw teeth, Figs. 6 and 7 show methods of removing dust and chips between saw blades, Figs. 8 and 9 show a circular saw and a band saw for producing long chips. Fig. 1 shows a circular saw with its discs 1 and 2 which are separately and independently driven by motors 5 and 6, respectively. The motors can be mechanically separated from each other or can consist of one single motor with transmissions and variable gears, all according to known technique. The saw blades are equipped with teeth 3, 4 made in general according to today's practice. A main requirement is that the teeth 3 on saw half 1 and the teeth 4 on saw half 2 must never intrude into the operating spaces of one another and make mechanical contact. The object 8 to be sawn, with its kerf 9, is moved on the saw table 10. Then the blade goes through the object 8 it usually gets a deflection towards one or the other side because of a structure of the material whic is oblique to the kerf. The sensor 7 indicates this deflection and is in Fig. 1 shown as two rollers, the common bearing housing of which gives th rollers a slight pressure against the saw blades. The movement of the bearing housing is used to vary the relative speed of the driving motors 5, 6 and thus the relative speed of the rows of teeth 3, 4. The row which cuts faster gest less engagement of the teeth and consequently lower cutting forces including their side components. The slower row of teeth gets more engagement of the teeth with higher cutting forces and thus higher side components. Moreover, the side-cutting forces for the two row are decreased and increased, respectively, and thus the angle 45 in Figs. and 5, not always but usually, should be larger than 90°. It can simply be said that the row of teeth which cuts faster leaves a void which allow the slower teeth row to press the blades in the direction of this void. Thus, when using known automatic control systems the deviation from a straight kerf can be kept small. Fig. 2 shows two embodiments of a band saw with the saw blades 1 an 2, pulley wheels 21, 22 and 23, 24 and the driving motors 5 and 6. The tw embodiments imply no principal differences. In the embodiment with symmetrically placed driving equipment for the blades 1 and 2, guiding pulleys 25, 26 are usually needed in order to keep the blades close to ea other. The sensor 7 for the blade deflections controls the speed of the teeth and thus the form of the kerf as shown in Fig. 1. Fig. 3 shows schematically a frame saw according to the same principle. The bands 31, 33 and 35 are pulled by means of a common frame by a motor 37, whereas the bands 32, 34 and 36 cooperating therewith have one frame and a driving motor each 38, 39 and 40. The speeds of the separate driving motors relative to the motor in common, 37, are controll in the same way as in previous Figures by one sensor each 7, not shown, s that all kerfs 9 in the sawn object 8 will be straight, or are given the desired curve as described below. Fig. 4 shows essentially the teeth of a pair of band saw blades 1, 2, where the teeth have been made from the same material as the blades themselves, which is common for frequent smaller band saw blades. The design differs, however, so that the rows of teeth 41 and 42 are not set symmetrically to the rows 43 and 44 but are left straight. As the blades 1, 2 can be driven with considerably different speeds the teeth must not be permitted to hook into one another. Fig. 4 further shows that the top angle to the saw direction 45 should be larger than 90° so that the teeth shall have a tendency to press the band package together, in order to obtain distinct sideforce components to produce the narrowest possible kerf and thus least possible waste and to avoid larger quantities of sawdust to penetrate between the blades. A small quantity of sawdust is desirable for lubrication. Fig. 5 shows an embodiment where the cutting teeth are soldered into cut seats on the blade in a known way, and where the angle 45 is larger than 90°. When sawing certain materials a thin disc or flakes of the material are produced which penetrate into the slot between the teeth 53, 54 and further between the saw blades 1 and 2 without being disintegrated. This is avoided according to Fig. 5 by means of internal teeth 56 in one of the saw halves 2, said teeth passing freely into the channel 55 which extends through all teeth 53 in the other saw half 1. All non-pulverized intruding parts of the saw object are thus broken and cut into dust. The assymetry could have been made on the top of the pair of teeth but this would have caused a tendency to inclined guidance. A thin layer of sawdust between the cooperating saw blades gives a certain desirable lubrication that generally eliminates contact between metal surfaces with different speeds. The layer, however, must not become so thick that on one hand the width of the kerf is unnecessarily widened, and on the other hand that fastening and guiding parts for the saw blades are unnecessarily stressed. The non-cutting inner parts of the teeth can have the edges obliquely ground either to guide the sawdust inbetween the blades for lubrication or to throw the dust to the outside of the blades or to carry the dust until the tooth has passed the saw object. In cases when too much sawdust tends to penetrate between the saw blades special means are needed to remove the dust. For band saw blades there is plenty of space for means that scrape, brush, blow and suck the blade cleans of dust known per se. For circular saw blades there is a possibility to press air, or in special cases a liquid, centrally, for example through a hollow driving shaft to one of the saw halves. The dust is then discharged at the periphery. At the same time a desirable small distance between the blades can be maintained by the air or liquid pressures, respectively. The two circular saw blades can also be provided with holes accordin to Figs. 6 and 7. The holes 61 on one blade and those 62 on the other blad are as widely as possible spread over the surfaces so that every unit of area on the two discs at least once for each turn is opposed to an opening in the other disc. To retain as much as possible of the metal discs it should be observed that two holes on one disc should not cover the same surface on the other disc. Fig. 6 shows an embodiment with six holes. If for example the numbe of holes is doubled the diameter of the holes can be reduced to one half and consequently the total removed surface to one half. According to Fig. 7 grindings 73 which from the edge have penetrated between the blades are discharged through holes 61 and 62. At least the trailing edges 71, 72 of the holes as seen in the direction of movement, can be incl ned towards the outside to prevent them from cutting the objec to be sawn. The discharge of grindings 73 becomes faster when the speed difference between the blades increases. The holes can also be made cuttin for simultaneous planing of the sawn surface. Besides the object to decrease the quantity of waste it is desired to obtain as long chips as possible, with unbroken fibres, to be used in strong fibreboards. When sawing perpendicular to the direction of movement each tooth cuts the fibre to a length which corresponds to the movement of the object during the time it takes for a tooth to pass. The only possibility to increase the content of long chips with unbroken fibres is to decrease the angle to the line between two teeth points and the saw direction to as close to zero as possible. Circular saws are usually arranged as in Fig. 1 with a saw table as close to the driving shaft as possible so that thin logs are sawn almost perpendicularly to the direction of movement of the log. Only very thick logs give a considerable quantity of long chips since they reach the upper edge of the saw blade. Fig. 8 shows a saw table 10 placed below the axle and with the saw teeth scarcely projecting below the plane of the saw table 10. With the expression "saw table" is meant at least an imaginary lower limiting sur¬ face for the log irrespective of the design of the means for moving the log. Since the log is positioned as close to the periphery of the saw disc as possible the obtained content of long chips is maximal. It is of course possible to use the arrangement of Fig. 8 with common single blades but th risk to obtain obl que kerfs is greater here than in the arrangement accor ding to Fig. 1. The method is suitable only with automatic guidance of a pack of saw blades. Fig. 8 shows a suitable position of the sensor 7 which indicates the deflection of the saw blades after the object 8 has passed. For band saws the only method to increase the length of the chips is to tilt the blades 1, 2 as much as possible relative- to the log 8. The length of passage of the blades through the log is thereby increased. A single unguided band then runs an increased risk of generating curved kerfs. Only the method described here with control of the relative speed o the blades in a pack makes the method in Fig. 9 suitable. The smaller the angle is the longer the chips will be. The sensor 7 and other arrangements have the same function as in Fig. 2. The driving of the motors 5 and 6 in previous Figures is to be controlled either by the sensor 7, or manually, or by means of a computer program. When sawing curved kerfs the program is superimposed on the information from the sensor 7. The sensor can be mechanical as described in connection with Fig. 1. In suitable cases it can also indicate the deflection of the saw blades magnetically, electrically or optically, without mechanical contact. Control systems for motors controlled by such sensors are well known and used in other applications. An embodiment will now be briefly described with reference to Fig. 2. An electronic control system 27 is indicated which is controlled by magnetic sensors 7. From the control system 27 the motors 5 and 6 are supplied with three-phase power electronically generated, the frequency of which is specific and variable for each motor. Since the speed of the motors is controlled by the frequency the relative speeds of the saw blade 1, 2 is controlled by the position of the blade pack in the air gap betwee the two coil systems of the sensor 7. When the band pack is positioned in the middle of the air gap the motors are fed with the same frequency. In order to get a quick rotation speed control the three-phase frequencies ar usually higher than normal mains frequency, thereby permitting the motors to be given smaller dimensions. The coils of the magnetic sensor 7 can be cast in plastic to resist blows and shocks. The arrangement is known for long and used in other applications. The output signals of the sensor 7 can be superimposed with signals from a computer program which .was stored when the log passed a measuring station. Here the natural bends of the log have been measured and the data are stored in the program. The sensor 7 all the time controls that the thickness of the sawn planks is constant. The superposition from the computer program solely ensures that the lateral movements of the log on the table correspond to the cutting direction of the saw blade. The invention has generally been described in connection with the sawing of wooden logs but can of course be applied also to the sawing of for example plastic a ' nd metals.

Claims: Cl aims 1. A method for guiding saw blades with at least two rows of cutting teeth which work in the same kerf close to each other and where the saw is guided sideways in a desired direction or to compensate for deviations fro a straight line caused by knots or similar, characterized in that the relative speed of the two rows of cutting teeth in the direction of movement through the piece of material to be sawn is intentionally varied so that the teeth of the faster row becomes less engaged and consequently will be subject to smaller cutting forces, whereby the resultant of the side forces perpendicular to the cutting forces will be directed towards the faster row of teeth, which causes the saw to move in a direction towards the faster row of teeth, or alternatively the piece of material to be sawn to move towards the slower row of teeth. 2. A method according to claim 1, applied to two toothed circular sa blades (1,2) or saw bands (1,2) arranged to have the rows of teeth (3,4) close to each other without mutual contact in the direction of movement of the saw teeth, and with the blades driven by separate motors or by a commo motor by means of a variable transmission, characterized in that the relative speed of the teeth is controlled manually or by a stored computer program to cause the kerf to follow a previously planned cut with desired, also non-linear parts. 3. A method according to claim 1, with sensors (7) which react on deviations from the desired form of the saw cut, characterized in that the sensor produces output signals which control the relative speed of the row of teeth. 4. A method according to claim 3, characterized in that the sensor arrangement (7) consists of one sensor on each side of the saw, consisting of optical, mechanical, magnetic or capacitive sensors known per se. 5. A method according to any of the preceding claims, characterized in that the two saw blades are given different self-resonance frequencies.

Inventors: ASK WALDEMAR, SIVERS CARL, ASK, WALDEMAR, SIVERS, CARL
Applicants: VIGILANTIA AB, AB VIGILANTIA
Application year: 1985
Main classification: B27B1
IPC codes: B23D47, B23D55, B23D59, B23D61, B27B33