GB2052107A

GB2052107A - A method and an apparatus for controlling the feeding of a bandsaw blade

Info

Publication number: GB2052107A
Application number: GB8017637A
Authority: GB
Original assignee: Amada Co Ltd
Current assignee: Amada Co Ltd
Priority date: 1979-05-30
Filing date: 1980-05-29
Publication date: 1981-01-21
Also published as: SE8004073L; JPS55164415A; IT8067844A0; GB2052107B; AU5891480A; AU535041B2; SE442961B; IT1128784B; JPS5835814B2

Abstract

For the better use of the blade of a horizontal bandsaw, the ratio of the speed at which the blade 15 is fed into a workpiece M to the speed at which the blade 15 is driven is kept constant. A bandsaw blade rotating within a pivotable head 5 of a bandsaw is driven by a motor 37, at a speed measured by a tachometer generator 41. The desired speed Vf at which the blade is to be fed into the workpiece M is calculated by a computing unit 51 from a signal from a torque detector 49 and compared, by means of a comparator 53, with the actual blade feeding speed Vf' measured by an angle detector 55 at a pivot of the head 5. If the compared signals differ, a servovalve 61 adjusts the flow of hydraulic fluid to or from a hydraulic motor 33 which controls the rate of descent of the head 5 and therefore the blade feeding speed until the compared signals have the same value. <IMAGE>

Description

SPECIFICATION A method and an apparatus for controlling the feeding of a bandsaw blade DESCRIPTION OF THE INVENTION The present invention relates generally to horizontal bandsaws in which a saw head assembly carrying a bandsaw blade is lowered during cutting to feed the bandsaw blade into a workpiece. More particularly, the invention relates to a method and an apparatus for controlling the feeding of the blade in a horizontal bandsaw.

Horizontal bandsaws generally comprise a saw head assembly in which a flexible endless bandsaw blade is trained around a pair of wheels so that the blade may cut when the wheels are rotated. The saw head assembly may be raised and lowered about a hinge pin or along one or more guide posts towards and away from a base on which a workpiece is placed. This can be done by a driving means such as a hydraulic motor.

During cutting, the saw head assembly is lowered from a raised position toward the base so as to feed the blade travelling in the saw head assembly into the material to be cut which is placed on the base. In most current horizontal bandsaws the saw head assembly is raised by a hydraulic motor having a piston and cylinder, when hydraulic fluid is supplied into the cylinder. It can be lowered by gravity when hydraulic fluid is drained from the hydraulic motor.

In such horizontal bandsaws the blade is fed, in an adjustable manner, into the material to be cut; whether it is fed at a high or low blade speed and with a large or small feeding force depends on the nature of the material. Generally, the blade is fed at a high speed and with a small force when cutting normal, easily cut materials, which are generally soft and brittle; it is fed at a low speed and with a large feeding force when cutting materials which are difficult to cut and which are, generally, hard and tough.

It is important to feed the bandsaw blade into the workpiece in such a way that cutting may always be performed at a certain fixed or uniform optimum cutting rate, which is defined the area (in square millimetres), of cut per unit time. Since many workpieces such as round bars and shaped lengths of steel vary in cross-sectional length as they are cut, it is necessary to correlate the feeding of the blade with the cross-sectional length of the workpiece as it is being cut: this enables the blade to cut at a predetermined optimum cutting rate. If the blade is not fed at the optimum cutting rate for the cross-sectional length of the workpiece being cut, the blade will work too hard, become prematurely worn and work inefficiently.

Conventionally, in order to cut at a fixed rate, which depends on the cross-sectional length of the workpiece being cut, the blade is fed with a fixed load or feeding force by means of the socalled load control or pressure control. In order to keep the load or feeding force fixed by means of the load control, the pressure of the hydraulic motor for the saw head assembly is controlled when the saw head assembly is lowered to feed the bandsaw blade into the workpiece material.

The load control is intended to maintain the cutting resistance fixed so as to feed the bandsaw blade at a fixed cutting rate, since the cutting rate is generally proportional to the cutting resistance.

Thus, with a conventional load control, the rate of feeding the bandsaw blade depends upon the cross-sectional cut length of the workpiece so as to keep the cutting resistance fixed; the driven speed of the blade is meanwhile kept constant.

Such a conventional load control, however, is defective, mainly because it is based on the premise that the cutting resistance per unit of amount of blade fed which is defined as feeding speed of the blade divided by the speed at which the blade is driven is always fixed or uniform. In fact, the cutting resistance per unit of amount of blade fed has a tendency to increase as the feeding speed or rate decreases. For example, when the feeding speed or rate is decreased in response to an increase of the cross-sectional length of the workpiece so as to keep the cutting resistance fixed, the cutting resistance per unit of amount fed will have a tendency to increase. The cutting resistance per unit of amount fed will markedly increase when cutting materials such as stainless steels which are difficult to cut and which have to be cut at a low blade feeding speed.

Thus, materials which are difficult to cut can be cut at a uniform optimum cutting rate by a conventional load control in a horizontal bandsaw although easily cut materials, which can be cut at a higher feeding speed, can also be cut at a substantially uniform cutting rate.

The present invention enables the provision of a method and an apparatus for controlling the feeding of a blade in a horizontai bandsaw so that the blade may always be fed at a uniform optimum cutting rate in correlation with the length of the cross-section cut of the workpiece, regardless of the nature of the workpiece material.

The present invention therefore also enables the provision of a method and an apparatus for controlling the feeding of a blade in a horizontal bandsaw, whereby the cutting efficiency can be markedly increased.

The present invention further enables the provision of a method and an apparatus for controlling the feeding of a blade in a horizontal bandsaw, whereby the life of the blade can be markedly increased.

According to a first aspect of the present invention there is provided an apparatus suitable for controliing a blade in a bandsaw, which apparatus comprises means for determining the speed at which, in use of the bandsaw, the blade is fed into a workpiece, means for determining the speed at which, in use of the bandsaw, the blade is driven and means for keeping constant the ratio of the said speed at which tile blade is fed into the workpiece to the said speed at which the blade is driven.

According to a second aspect of the present invention there is provided a bandsaw comprising a base assembly adapted to support a workpiece, a saw head assembly having a drivable bandsaw blade and adapted to move with respect to the base to feed the blade into a workpiece supported by the base assembly, means for determining the speed at which, in use of the bandsaw, the blade is fed into the workpiece, means for determining the speed at which, in use of the bandsaw, the blade is driven and means for keeping constant the ratio of the speed at which, in use of the bandsaw, the blade is fed into the workpiece to the speed at which, in use of the bandsaw, the blade is driven.

According to a third aspect of the present invention there is provided a method of controlling the blade of a bandsaw, which method comprises the step of keeping constant the ratio of the speed at which the blade is fed into a workpiece to the rate at which the blade is driven.

According to a fourth aspect of the present invention there is provided a method of controlling the feeding of the blade of a horizontal bandsaw wherein the ratio of the blade feeding speed to the speed at which the blade is driven is kept constant during cutting of a workpiece so as to maintain the cutting rate constant.

According to a fifth aspect of the present invention there is provided an apparatus for controlling the feeding of the blade of a horizontal bandsaw, which apparatus comprises a detecting means for detecting the cutting resistance in the cross-sectional length of a cut in a workpiece being cut, a feeding speed controlling means and a blade speed controlling means for keeping constant the ratio of the feeding speed to the speed at which the blade is driven based upon the cutting resistance detected by the said detecting means, a controlling means which acts in accordance with controlling signals given by the said feeding speed controlling means and which controls the feeding speed and a controlling means which acts in accordance with controlling signals given by the said blade speed controlling means.

According to a sixth aspect of the present invention, there is provided a method for controlling the feeding of the blade of a horizontal bandsaw wherein the ratio of the blade feeding speed to the speed at which the blade is driven is kept constant by keeping the cutting power constant so as to keep the cutting rate constant.

According to a seventh aspect of the present invention, there is provided an apparatus for controlling the feeding of the blade of a horizontal bandsaw, in which apparatus a power controlling means is connected to a motor for driving the bandsaw blade, a controlling means for keeping constant the ratio of the blade feeding speed to the speed at which the blade is driven is connected to the said motor and the driving wheel and a feeding speed controlling means for controlling the blade feeding speed is connected to the said controlling means.

For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a front elevational view of a horizontal bandsaw in which the principles of the present invention can be embodied; Figure 2 is a diagram showing the feeding of the blade used in the horizontal bandsaw shown in Figure 1; Figures 3a and 3b are graphs each showing the blade driven speed as a function of the feeding speed of the blade; and Figures 4, 5, 6, 7 and 8 are diagrammatic views of control systems of horizontal bandsaws, such as that shown in Figure 1, embodying the principles of the present invention.

Referring now to Figure 1 , there is shown a horizontal bandsaw which is generally designated by the numeral 1 and which comprises a box-like base 3 and a saw head assembly 5, which is movable towards and away from the base 3 as is conventional. The saw head assembly 5 includes a driving wheel 7 and a driven wheel 9 having shafts 1 1 and 13, respectively, around which an endless bandsaw blade 1 5 is trained. The blade 15 may be driven for cutting when the driving wheel 7 is driven by power. The blade 15 is held or guided, by a pair of guide assemblies 17 and 19 fixed to guide arms 21 and 23 respectively, so that it may slide with its cutting edge facing downwards. The guide arms 21 and 23, are adjustably held by a beam member 25 which is fixed at the upper portion of the saw head assembly 5.A work-table 27 is mounted on the base 3 to receive a workpiece M. A vice assembly 29 having a fixed jaw 29f and a movable jaw 29m is also mounted on the base 3 to hold the workpiece. The saw head assembly 5 is pivotally connected to the base 3 by means of a hinge pin 31 and can be raised away from and lowered towards the base 3 by means of a hydraulic motor 33 of the piston and cylinder type having a rod 35. However, the saw head assembly 5 can instead be vertically raised from and lowered towards the base 3 along one or more vertical guide posts by a hydraulic motor or other means, as will be disclosed hereinafter. In either case, when the saw head assembly 5 is lowered from its raised position as shown by the imaginary lines in Figure 1, the blade 15 rotating around the driving wheel 7 and - the driven wheel 9 in the saw head assembly 5 will be fed into and cut the workpiece M which is held by the vice assembly 29 on the work-table 27.

Referring to Figure 2, the feeding of the blade 15 will be theoretically and mathematically examined, and the cutting resistance, the feeding and driven speeds the feeding amount of the blade and the cutting rate will be considered. In Figure 2, the blade 15, with a distance between teeth (tooth pitch) of p, is shown as being driven along the Xaxis as shown by the arrow and fed along the Yaxis by an amount h as shown by the arrow and also cutting into the w#orkpiece M at a cutting angle S.

First of all, it can be seen that: dy h tan0=~=~ (1) dx p where h is the amount fed and p is the tooth pitch.

Rearranging equation (1): 1 dy dy dt dy dx h=p~--=p~~--~-==p.--.-- (2) dx dt dx dt dt Thus, Vf (3) Vt where Vf is the speed of feeding the blade into the workpiece and Vt is the speed at which the blade is driven.

The cutting resistance per tooth (r) may be expressed as: r=A.h (4) where A is a constant which is to be obtained experimentally.

The total cutting resistance (R) may be expressed as R=r.n (5) where n is the number of teeth in the cut.

Substituting equation (4) in equation (5), we obtain R=A.h.n (6) The cross-sectional length (L) of the cut in a workpiece M being cut can be expressed as follows: L=p (7) L .-. n =~ (8) p Substituting equation (8) in equation (6) gives an expression for the total cutting resistance (R): hL R=A~-- (9) p From equation (3), can be substituted to give: p-Vf L R=A. - (10) Vt P # R.Vt=A.Vf.L (11) The cutting rate (t7) of horizontal bandsaws is defined as follows:~ S (12) T where S is cut area and T is time.

Now, from equation (11) we have: R.Vt=A.Vf.L (11) but h Vf= T h R.Vt=A.-.L T S T T =A~# (13) The cutting power (H) can be expressed as: H=R.Vt (14) But from equation (13), R-Vt=A-X7 (13) H=A~# (15) that is to say, the cutting power is proportional to the cutting rate.

From the above analysis, it will be understood from equation (15) that the cutting rate (#) can be kept constant if the cutting power (H) is kept constant. In a method according to the present invention, the cutting power (H) is kept constant so as to keep the cutting rate (#) fixed or uniform according to equation (15). Also, the ratio of the speed at which the blade is driven (Vt) to the feeding speed (Vf) is kept constant so as to keep the amount fed (h) fixed in equation (3).Thus, when the cutting resistance (R) increases because or an increase of the length (L) of the crosssectional cut in the workpiece M being cut, the feeding speed (Vf) drops and, simultaneously, the speed at which the blade is driven (Vt) also drops in proportion to the feeding speed (Vf) so as to keep the cutting power (H) (= the cutting resistance (R) x the speed at which the blade is driven (Vfl fixed. This can be done satisfactorily so long as the amount fed (h) of equation (3) is kept constant.

The trouble is, however, that the amount fed (h) is not certain to be kept constant and may erroneously increase for some reason when the speed at which the blade is driven (Vt) drops, for example. Consequently when the cutting resistance tR) increases because of an increase of the length (L) of the cross-sectional cut in the workpiece M and the speed at which the blade is driven stops so as to keep the cutting power (H) constant, the amount fed (h) increases, thereby causing the cutting resistance to increase further.

If the amount fed (h) increases when the speed at which the blade is driven (Vt) drops to reduce the cutting resistance (R) in order to keep the cutting power (H) constant, the cutting resistance (R) will increase further and so make it necessary to drop the speed at which the blade is driven (Vt) again.

Referring to Figures 3a and 3b, which are graphs, in order to decrease the amount fed (h) by an amount depending on the reduction of the speed at which the blade is driven, a gang control function (K) of the feeding speed (Vf) and the speed at which the blade is driven (Vt) is set up.

In the graphs of Figures 3a and 3b, the feeding speed (Vf) and the speed at which the blade is driven (Vt) are shown on the x and y axes respectively, and the gang control function (K) is shown as a straight line in Figure 3a and as a curve in Figure 3b. Thus, the following equation is expressed: Feeding Amount (h) Feeding Speed (Vf) cot 0 Blade Driven Speed (V.) (16) When the ratio of the feeding speed (Vf) to the speed at which the blade is driven (Vt) increases, 0 will decrease and the amount fed will increase.

When the ratio of the feeding speed (Vf) to the speed at which the blade is driven (Vt) decreases, 0 will increase and the amount fed will decrease.

Thus, the variation of the amount fed (h) can be minimised by controlling the relation between the speed at which the blade is driven (Vt) and the feeding amount (h); however, the feeding amount (h) can be not completely kept constant.

The equation of the straight line of the gang control function (K) of Figure 3a, for example, is expressed as W=D.Vf+E (17) where D and E are experimentally obtained constants. Also, the speed at which the blade is driven (Vt) can be expressed as a function of the feeding speed: Vt = f (Feeding Speed) (18) where f is a function showing the relation of the speed at which the blade is driven ( ) to the feeding speed (Vf).By substituting equation (18) in the equation (13), the following equations can be obtained: R ~ f (Feeding Speed) = A at (19) A~# f (Feeding Speed) = (20) R A~# Feeding Speed (Vf) = r1 ( ) (21) R Referring now to Figure 4, a first embodiment of the present invention will be described with reference to the horizontal bandsaw 1 as shown in Figure 1, in which the saw head assembly 5 is raised and lowered about the hinge pin 31 by the hydraulic motor or cylinder 33.

In this embodiment, the driving wheel 7 is driven by a motor 37 through a speed change unit 39, and a tachometer generator 41 is connected to a point between the driving wheel 7 and the speed change unit 39 by means of gears 43 and 45. The tachometer generator 43 is connected to a blade speed controlling unit 47 for giving feedback signals to and controlling the speed change unit 39. Also, a torque detector 49 is provided between the tachometer generator 41 and the driving wheel 7, and is connected for the purpose of giving signals, to a feeding speed computing unit 51. The feeding speed computing unit 51 obtains the feeding speed (Vf) of the bandsaw blade 1 5 using the signals given by the torque detector 49 and using equation (21) which has been described hereinbefore. Also, the feeding speed computing unit 51 is connected to a comparator 53 which it supplies with the obtained feeding speed (Vf).

An angle detector 55, such as an encoder, for detecting the lowering angle or angular position of the saw head assembly 5 is connected to the hinge pin 31, and it is also connected to an actual feeding speed computing unit 57. The angle detector 55 gives signals to the actual feeding speed computing unit 57 about the angular position of the saw head assembly 5 during cutting. The actual feeding speed computing unit 57 can store shapes and dimensions of work pieces to be cut and type and dimensions of the horizontal bandsaw 1. It also obtains actual feeding speed (Vf') of the blade 15 using the signals given by the angle detector 55 and the stored information. Also, the actual feeding speed computing unit 57 is connected to the comparator 53 and a blade speed computing unit 59 to give them the actual feeding speed (Vf').

The comparator 53 compares the feeding speed (Vf) given by the feeding speed computing unit 51 and the actual feeding speed (Vf') and controls a servovalve 61 through a servovalve controlling unit 63 according to the difference between (Vf) and (Vf'). The servovalve 61 controls the hydraulic motor 33 so as to control the feeding speed (V) ofthe blade 15.

The blade speed computing unit 59 is connected to the blade speed controlling unit 47, and obtains the optimum speed at which the blade is to be driven (Vt) using a given desired feeding amount (hx) and the actual feeding speed (Vf') and also using the equations (16) and (18) described hereinbefore. The blade speed computing unit 59 gives the obtained blade driven speed (Vt) to the blade speed controlling unit 47.

In order to control the feeding speed (W) and the driven speed (Vi) of the bandsaw blade 1 5, the transmitting torque of the driving wheel 7, that is the rotary driving force, is taken as the cutting resistance (R) by the torque detector 49 and is given to the feeding speed computing unit 51.

Then the feeding speed (Vf) is obtained by the feeding speed computing unit 51 using the equation (21), that is W= f-'(A Ti/P). The value of the cutting resistance 'R) given by the torque detector 49 and the stored desired cutting rate (hx) are used. The feeding speed (Vf) is transmitted to the comparator 53. The angular position of the saw head assembly 5 is transmitted by the angle detector 55 to the actual feeding speed computing unit 57.The actual feeding speed (or') is therefore obtained by the actual feeding speed computing unit 57 using the angular position of the saw head assembly 5 given by the angle detector 55, the shape and dimension of the workplace M and information on the type and dimensions of the horizontal bandsaw. Then the actual feeding speed (Vf') is transmitted to the comparator 53 and the blade speed computing unit 59.

After this, the comparator 53 compares the two feeding speeds (Vf) and (Vf') and controls the hydraulic motor 33 through the servovalve controlling unit 63 and the servovalve 61 so as to make the two feeding speeds (Vf) and (Vf') approximate or equal to each other to control the feeding speed (Vf) of the blade 1 5. On the other hand, the blade speed computing unit 59 obtains the speed at which the blade 15 is driven (Vt) of tile using equations (16) and (18) and using the actual feeding speed (Vf') given by the actual feeding speed computing unit 57 and the desired feeding amount (hx).The speed at which the blade is driven (Vt) obtained by the blade speed computing unit 59 is fed to the blade speed controlling unit 47 so as to enable it to control the speed at which the blade is driven (Vt) through the speed change unit 39.

Referring to Figure 5, a second embodiment will now be described. In this embodiment, the saw head assembly 5 can be raised and lowered by the hydraulic cylinder 33 vertically along one or more guide posts (not shown). Since this second embodiment is of course similar in principle to the embodiment shown in Figure 4, elements common to both the embodiments will be referred to by common reference numerals.

In the second embodiment, the driving wheel 7 for driving the blade 15 is shown to be driven by a servomotor 65 through a reduction gear unit 67.

The servomotor 65 has the functions of both the motor 37 and the speed change unit 39 of the first embodiment shown in Figure 4, although the reduction gear unit 67 is still needed. The motor 37 and the speed change unit 39 of the first embodiment can therefore be used as the servomotor 65 and the reduction gear unit 67. The servomotor 65 is controlled by the blade speed controlling unit 47, which determines the speed at which the blade 1 5 is driven (Vt) in a similar manner to the speed change unit 39 of the first embodiment. Also as in a similar manner to the first embodiment, a tachometer generator 41, connected to the shaft cf the servomotor 65 through gears 43 and 45, is connected to the blade speed controlling unit 47.A blade speed computing unit 59 is also connected to the blade speed controiling unit 47. The speed at which the blade 15 is driven (vet) is thus controlled by the blade speed controlling unit 47 and the blade speed computing unit 59 in a similar manner to the first embodiment.

In order to detect the speed of descent of the saw head assembly, that is the feeding speed of the blade 1 5, there is provided a tachometer generator 69 having a gear or pinion 71 which is in engagement with a rack 73 secured to the saw head assembly 5. The rack 73 is vertically disposed, parallel with the guide post or posts for the saw head assembly 5, and is shown in Figure 5 as being connected to 1-he piston and rod 35 of the hydraulic motor 33. The tachometer generator 69 is connected to a feeding speed controlling unit 75 which controls, through a driving means such as a motor 77, a flow control valve 79 which is provided in a drain passage 81 of the hydraulic motor 33 for controlling the feeding speed of the blade 15.The saw head assembly 5 is lowered when hydraulic fluid is drained from the cylinder of the hydraulic motor 33 and the flow control valve 79 controls the drainage flow of hydraulic fluid, thereby to controls lhe speed descent of the saw head assembly 5 (which is the feeding speed of the bandsaw blade 1 5).

A pressure detector 83 is connected to the interior of the cylinder of the hydraulic motor 33 and transmits information on the pressure in the cylinder of the hydraulic motor 33 to a cutting resistance computing unit 85, to which it is also connected. The cutting resistance computing unit 85 computes the cutting resistance (R) using the eauation R = W - ~ P wherein W is the weight of the saw head assembly 5. P is the pressure within the cylinder of the hydraulic motor 33, A is the working area of the piston and rod 35 of the hydraulic motor 33 and R is the vertical cutting resistance. The cutting resistance computing unit 85 transmits the pressure of the hydraulic motor 33 to a feeding speed computing unit 51, to which it is also connected.The feeding speed computing unit 51 obtains the feeding speed (Vf) from the cutting resistance (R), given by the cutting resistance computing unit 85, and the desired cutting rate (x) using equation (21 ) (Vf=f-1(A ./R)) and gives the obtained feeding speed (Vf) to the blade speed computing unit 59 and the feeding speed controlling unit 75.

In order to control the feeding speed (Vf) and the driven speed (Vt) of the blade 1 5 in the second embodiment, first of all the cutting resistance (R) is obtained by the cutting resistance computing unit 85 from the hydraulic pressure given by the pressure detector 83 using the equation R = W ~ P described above. The feeding speed (Vf) is then obtained by the feeding speed computing unit 51 from the cutting resistance (R), given by the cutting resistance computing unit 85, and the desired cutting rate (qx) using equation (21) (V=f f-1(A Ti/P)). The feeding speed (Vf) obtained by the feeding speed computing unit 51 is transmitted to the feeding speed controlling unit 75 and the blade speed computing unit 59.The feeding speed controlling unit 75 will control hydraulic fluid draining from the hydraulic motor 33 by means of the motor 77 and the flow control valve 79; the descent of the saw head assembly 5, and therefore the feeding speed (Vf) of the bandsaw blade 15, are thus controlled. On the other hand, the blade speed computing unit 59 will obtain the blade driven speed (Vt) from the feeding speed (Vf) given by the feeding speed computing unit 51 and the desired feeding amount (hx) using equations (16) (h = Vf/Vt = cot 0) and (21 ) (Vt = f(feeding speed)) and give this value to the blade speed controlling unit 47.The blade speed controlling unit 47 will control the servomotor 65 in a manner depending on the speed at which the blade is driven (Vt) given by the blade speed computing unit 59 and will thereby control the speed (Vt) at which the blade 1 5 is driven. The speed at which the blade is driven (Vt) and the feeding speed (Vf) are fed back to the blade speed controlling unit 47 and to the feeding speed controlling unit 75 respectively, by means of the tachometer generators 41 and 69 respectively.

Referring now to Figure 6, a third embodiment will now be described. In this embodiment the cutting head assembly 5 is vertically raised by means other than the hydraulic motor 23 used in the first and second embodiments. Since this third embodiment is very similar both in construction and in function to the second embodiment shown in Figure 5, elements common to the second and third embodiments will be given the same reference numerals and will not be described in detail.

In the third embodiment, the saw head assembly 5 can be vertically raised and lowered by a servomotor 87 acting through a reduction unit 89 and by means of a pinion 91 and a rack 93.

The rack 93 is vertically secured to, and movable with the saw head assembly 5. The pinion 91 engages the rack 93 so that it may raise and lower the rack 93 together with the saw head assembly 5 when driven by the servomotor 87. A gear 88 is provided between the servomotor 87 and the reduction unit 89. A tachometer generator 69 having a gear 71 and being of the same nature as that used in the second embodiment has its gear 71 is in engagement with the gear 88. The tachometer generator 69 takes the lowering speed of the saw head assembly 5, that is the feeding speed of the blade 1 5, and gives the feeding speed to a feeding speed controlling unit 75, to which it is connected.The feeding speed controlling unit 75 is connected to and controls the servo-motor 87 so as to control, by means of the pinion 91 and the rack 93, the speed of descent of the saw head assembly 5, that is the feeding speed of the bandsaw blade 1 5.

In order to detect the vertical cutting resistance (R) load detecting means 95, such as pressure elements, are disposed between at the guide assemblies 17 and 19 so as to detect the cutting resistance or reaction through the back of the blade 15 during cutting. The load detecting means 95 transmits the cutting resistance (R) to a feeding speed computing unit 51, which obtains the feeding speed (Vf) from the cutting resistance R given by the load detecting means 95 and the desired cutting rate (77x) using equation (21) (Vf= f-1(A ~ rllR)). To transmit the obtained feeding speed (Vf), the feeding speed computing unit 51 is connected to the feeding speed controlling unit 75 and a blade speed computing unit 59: this is similar to the arrangement described in the second embodiment.

From the above description, it will now be understood that the feeding speed (Vf) of the blade 1 5 is controlled, by means of the servomotor 87, by the feeding speed controlling unit 75 from the feeding speed (Vf) given by the feeding speed computing unit 51. Also, it will be readily apparent that the speed at which the blade is driven (Vt) is controlled in a manner depending on the value of the speed at which the blade is driven (Vt) obtained by the blade speed computing unit 59 in a similar manner to the second embodiment.

In a fourth embodiment, a motor 97 having an output shaft 99 for driving the blade 1 5 is controlled by a power controlling unit 101 to keep the cutting rate (q) fixed or uniform, based on the principle described above. As can be seen from Figure 7, the motor 97 is connected to the shaft 11 of the driving wheel 7 by means of a coupling means 103 and a connecting shaft 105.

There is provided a differential gear unit 107 which has an output shaft 109 and is connected to the coupling means 103 by a connecting shaft 111. A constant speed motor 11 3 is connected to the differential gear unit 107 by its output shaft 11 5. The output shaft 109 of the differential gear unit 107 is connected to a speed change unit 11 7 having an output shaft 11 9. The output shaft 11 9 is connected to a metering valve 121 provided in the drainage passage 81 of the hydraulic motor 33 for raising and lowering the saw head assembly 5. The metering valve 121 exhausts hydraulic fluid from the cylinder of the hydraulic motor 33 according to the rotation rate and the stroking length of the plunger.

When the motor 97 for driving the bandsaw blade 15 is controlled by the power controlling unit 101 according to the desired cutting rate ('7), the rotation rate of the output shaft 109 of the differential gear unit 107 is expressed as N1 - N2 where N, is the rotation rate, of the output shaft 99 of the motor 97 and N2 is the rotation rate of the constant speed motor 113. When the speed change unit 11 7 is set to a change gear ratio (G) according to the amount fed (hx), the rotation rate N1 - N2 of the output shaft 109 is changed to (N1 - N2). G Grotations per unit of time.Thus, in order to control the feeding speed (Vt) of the bandsaw blade 1 5, hydraulic fluid drained from the cylinder of the hydraulic motor 33 when the saw head assembly 5 is being lowered is controlled by the metering valve 121 which is rotated at (N1 - N2)G revolutions, as set by the speed change unit 117. As is readily apparent, the feeding speed (Vt) of the bandsaw blade 15 is controlled by the equation (17) (Vt = DxVf + E), which may be rearranged as Vf= (Vt - E)/D. In order to adjust the amount fed (h), it is possible to change the displacement of the metering valve 121 instead of changing the change gear ratio (G) of the speed change unit 117.

Referring to Figure 8, a fifth embodiment, which is similar to the fourth embodiment as shown in Figure 7, will now be described.

Elements common to the fourth and fifth embodiments will be given the same reference numerals and will not be described in detail.

In this embodiment, a motor 97 having an output shaft 99 and a power controlling unit 101 is connected to the shaft 11 of the driving wheel 7 by means of a coupling means 103 and a connecting means 105 in a similar manner to the fourth embodiment. A differential gear unit 107, having an output shaft 109 and connected to a constant speed motor 11 3 having an output shaft 11 5, is connected to the coupling means 103 by a connecting shaft 111 in a similar manner to the fourth embodiment.

The differential gear unit 107, however, is directly connected to a metering valve 121, which is provided in the drainage passage 81 of the hydraulic motor 33 so as to work in a similar manner to that of the fourth embodiment. There is another metering valve 123, which is connected by a connecting shaft 125 to another coupling means 127. The coupling means 127 is provided on the connecting shaft 111 between the coupling means 103 and the differential gear unit 107.

The metering valve 123 is connected by a passage 129 to a source of hydraulic fluid 131 through a flow control valve 133, of a pressure compensating type, for setting the cutting rate.

There is provided, between the flow control valve 133 and the metering valve 123, a hydraulic motor 135 having a piston and a rod 137 biased by a spring 139 against the hydraulic pressure in the passage 129. The piston and rod 137 of the hydraulic motor 135 are connected to the power controlling unit 101 which controls the motor 97 in such a manner as to control the voltage applied to the motor 97 in relation to the hydraulic pressure in the passage 129. The metering valve 123 is controlled by a hydraulic motor 141 which is provided in the drainage passage 81 of the hydraulic motor 33. The hydraulic motor 141 has a piston and rod 143 biased by a spring 145 against the hydraulic pressure in the drainage passage 81 and connected to the plunger of the metering valve 123. Thus, the metering valve 123 will allow the through flow of hydraulic fluid from the hydraulic source 131 to the hydraulic tank in inverse proportion to the hydraulic pressure in the drain passage 81. The voltage output of the power controlling unit 101 is therefore controlled by means of the piston and rod 137 of the hydraulic motor 135, movement of which is determined by the hydraulic pressure in the drain passage 81.

Claims

1. An apparatus suitable for controlling a blade in a bandsaw, which apparatus comprises means for determining the speed at which, in use of the bandsaw, the blade is fed into a workpiece, means for determining the speed at which, in use of the bandsaw, the blade is driven and means for keeping constant the ratio of the said speed at which the blade is fed into the workpiece to the said speed at which the blade is driven.

2. An apparatus according to Claim 1, wherein the means for determining the speed at which the blade is fed into a workpiece comprises means for determining the resistance encountered by the blade when fed into a workpiece.

3. An apparatus according to Claim 1 or 2, wherein the means for determining the speed at which the blade is driven comprises a tachometer generator.

4. An apparatus according to Claim 1, 2, or 3 wherein the means for keeping the said ratio constant comprises means for controlling the speed at which the blade is fed into a workpiece.

5. An apparatus according to any one of Claims 1 to 4, wherein the means for keeping the said ratio constant comprises means for controlling the speed at which the blade is driven.

6. A bandsaw comprising a base assembly adapted to support a workpiece, a saw head assembly having a drivable bandsaw blade and adapted to move with respect to the base to feed the blade into a workpiece supported by the base assembly, means for determining the speed at which, in use of the bandsaw, the blade is fed into the workpiece, means for determining the speed at which, in use of the bandsaw, the blade is driven and means for keeping constant the ratio of the speed at which, in use of the bandsaw, the blade is fed into the workpiece to the speed at which, in use of the bandsaw, the blade is driven.

7. A bandsaw according to Claim 6, wherein the means for determining the speed at which the blade is fed into a workpiece supported by the base assembly comprises means for determining the resistance encountered by the blade when fed into a worinpiece.

8. A bandsaw according to Claim 7, wherein the saw head assembly is pivotally movable with respect to the base assembly to feed the blade into a workpiece supported by the base assembly and wherein the means for determining the said resistance comprises means for measuring the torque of the pivotal movement

9. A bandsaw according to Claim 6, wherein the saw head assembly is translationally movable with respect to the base assembly to feed the blade into a workpiece supported by the base assembly and wherein the means for determining the speed at which the blade is fed into a workpiece supported by the base assembly comprise a rack and pinion arrangement and a tachometer generator operatively connected to the pinion.

10. A bandsaw according to any one of Claims 6 to 9, wherein the means for determining the speed at which the blade is driven comprises a tachometer generator.

11. A bandsaw according to any one of Claims 6 to 10, wherein the means for keeping the said ratio constant comprises means for controlling the speed at which the blade is fed into a workpiece.

12. A bandsaw according to Claim 11, wherein the saw head assembly is movable with respect to the base to feed the blade into a workpiece supported by the base assembly by a piston and cylinder arrangement, the cylinder being suitable for receiving hydraulic fluid, and wherein the means for controlling ;the speed at which the blade is fed into a workpiece comprises means for controlling the supply of hydraulic fluid to, or the drainage of hydraulic fluid from the cylinder.

13. A bandsaw according to any one of Claims 6 to 17. wherein the means for keeping the said ratio constant comprises means for controlling the speed at which the blade is driven.

14. A bandsaw according to Claim 13, wherein the blade is drivable by an electrically powerable motor and wherein the means for controlling the speed at which the blade is driven comprises means for regulating the voltage applied, and/or the current supplied, to the electrically powerable motor.

15. A bandsaw according to Claim 13 or 14, wherein the means for controlling the speed at which the blade is driven comprises differential gear means.

16. A method of controlling the blade of a bandsaw, which method comprises the step of keeping constant the ratio of the speed at which the blade is fed into a workpiece to the rate at which the blade is driven.

17. A method according to Claim 16, wherein the said ratio is kept constant by keeping constant the power at which the blade cuts the workpiece.

1 8. A method according to Claim 1 6 or 17, which method comprises the steps of determining the actual speed at which the blade is driven, calculating the desired speed at which the blade is to be fed into the workpiece, determining the actual speed at which the blade is fed into the workpiece, comparing the desired speed at which the blade is to be fed with the actual speed with which the blade is fed and altering the actual speed with which the blade is fed if it is not the same as the desired speed with which the blade is to be fed.

19. A method according to Claim 16, 1 7 or 18, which method additionally comprises the steps of calculating the optimum speed at which the blade is to be driven, comparing the optimum speed at which the blade is to be driven with the actual speed at which the speed is driven and adjusting the actual speed at which the blade is driven if it is not the same as the desired speed at which the blade is to be driven.

20. A method of controlling the feeding of the blade of a horizontal bandsaw wherein the ratio of the blade feeding speed to the speed at which the blade is driven is kept constant during cutting of a workpiece so as to maintain the cutting rate constant.

21. An apparatus for controlling the feeding of the blade of a horizontal bandsaw, which apparatus comprises a detecting means for detecting the cutting resistance in the crosssectional length of a cut in a workpiece being cut, a feeding speed controlling means and a blade speed controlling means for keeping constant the ratio of the feeding speed to the speed at which the blade is driven based upon the cutting resistance detected by the said detecting means, a controlling means which acts in accordance with controlling signals given by the said feeding speed controlling means and which controls the feeding speed and a controlling means which acts in accordance with controlling signals given by the said blade speed controlling means,

22.A method for controlling the feeding of the blade of a horizontal bandsaw wherein the ratio of the blade feeding speed to the speed at which the blade is driven is kept constant by keeping the cutting power constant so as to keep the cutting rate constant.

23. An apparatus for controlling the feeding of the blade of a horizontal bandsaw, in which apparatus a power controlling means is connected to a motor for driving a driving wheel for driving the bandsaw blade, a controlling means for keeping constant the ratio of the blade feeding speed to the speed at which the blade is driven is connected to the said motor and the driving wheel and a feeding speed controlling means for controlling the blade feeding speed is connected to the said controlling means.

24. An apparatus suitable for controlling the blade of a bandsaw substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 8 of the accompanying drawings.

25. A bandsaw substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 8 of the accompanying drawings.

26. A method of controlling a bandsaw blade substantially as hereinbefore described with reference to Figures 1 to 8 of the accompanying drawings.

27. A bandsaw whenever provided with an apparatus according to any one of Claims 1 to 5, 21,23 and 24.

28. A bandsaw according to any one of Claims 6 to 15. 25 and 27, which bandsaw is a horizontal bandsaw.

29. Any novel feature or combination of features described herein.