WO1990014915A1

WO1990014915A1 - Saw chain grinding machine

Info

Publication number: WO1990014915A1
Application number: PCT/SE1990/000381
Authority: WO
Inventors: Örjan RUNNZELL
Original assignee: Bethcke, Hans, Jochen; Gersch, Udo
Priority date: 1989-06-01
Filing date: 1990-06-01
Publication date: 1990-12-13
Also published as: SE8902011D0; SE8902011L

Abstract

A grinding machine for grinding endless saw chains (1) with left-hand and right-hand saw teeth comprises a feeding wheel (2) adapted to take up a saw chain (1) for feeding the teeth thereof to a grinding position, and a grinding wheel (10) which, in the grinding position, is engageable with a saw tooth for grinding the cutting edge thereof, characterised by a tensioning means (3) displaceable away from the feeding wheel (2) to engage the saw chain (1) and keep it tensioned on the feeding wheel both during feeding and during grinding; a first sensor (5) adjacent to the tensioning means (3) for sensing the displacement thereof and thus determining the length of the saw chain (1); a computer unit which is preprogrammed with information about the length, pitch, and number of saw teeth of standard saw chains, for determining the theoretical number of saw teeth of the saw chain (1) to be ground, the theoretical number serving to determine the total length of feed of the feeding wheel during grinding of the saw chain (1); and a second sensor (8) adjacent to the feeding wheel (2) for sensing the passing of the cutting edge of the cutting portion (12) of the saw teeth while the saw chain (1) is advanced by the feeding wheel (2), this sensing serving to control, by means of the computer unit, the feeding of the cutting edge of the saw tooth and the movement of the grinding wheel (10) to the grinding position.

Description

SAW CHAIN GRINDING MACHINE

The present invention relates to a fully automatic grinding machine for grinding endless saw chains with left-hand and right-hand sawteeth, said machine comprising a feeding wheel adapted to take up a saw chain for feeding the teeth thereof to a grinding position, and a grinding wheel which, in said grinding position, is engageable with a saw tooth for grinding said tooth.

The saw chains for various types of sawing machines usually become blunt after some time and then need to be ground or resharpened, preferably by means of a suitable grinding machine. For optimum sawing efficiency, prefer- ably for as long as possible, it is of great importance that the saw teeth are correctly ground or filed. Wrongly ground teeth lead to an increased wear, thus shortening the service life of the saw chains.

A usual inconvenience of existing grinding machines is that they must be adjusted to the type and size of the saw chain to be resharpened. Saw chains come in many different sizes, so-called pitches, and many different lengths. Thus, a new adjustment is required for every saw chain to be resharpened. Furthermore, the number of saw teeth to be ground on the saw chain has to be manually programmed to the existing grinding machines.

At present, there are semiautomatic machines which feed the saw teeth at regular intervals which have to be changed when other types of chains are to be ground. Also, these semiautomatic machines require that the saw teeth are uniformly spaced apart on the entire chain. However, saw chains are as a rule not constructed in this manner, and often there is a longer distance between the saw teet at one place. This is the case with all chains having an extra link owing to an odd number of drive links. Some¬ times, one or more saw teeth may even be missing. In such cases, the user is forced to find the extra link and star grinding from there. In present techniques, the user is thus compelled to adopt several manual operations which are both time-consuming and inconvenient.

An important parameter in grinding saw teeth is the so-called filing angle. A filing angle of 5-10° is pre¬ ferred for" optimum grinding efficiency. At present, there are two semiautomatic grinding machines. In the German variant, the filing angle is produced in that the grinding wheel is made to pendulate relative to the vertical line of the left-hand and the right-hand tooth, respectively.

The Swedish variant however presents no solution at all to this problem.

Since the saw chains used today have alternating left-hand and right-hand teeth, the position of the grinding" machine relative to the tooth has to be changed between the grinding of two successive teeth.

WO 88/09237 discloses an arrangement in automatic saw chain grinding machines. This machine comprises, inter alia, .a sensor which is provided on a stop finger and which, during feeding of the saw chain, is in contact with the upper side of said chain. When a saw tooth on the saw chain',has reached a position where the stop finger drops behind the rear end of the saw tooth (see Fig. 5), the feeding direction of the saw chain is automatically re- versed, and the saw tooth is moved slightly rearwards to a starting position from which it is advanced to a grinding position. In the grinding position, a manual adjustment according to the type of chain and the degree of wear is needed. Then, one side of the chain is automatically ground. In order to grind the other side, another manual adjustment is necessary. An important difference between this arrangement and that of the present invention is that, in the known arrangement, the rear portion of the saw tooth is sensed, i.e. the passing of the saw tooth is detected, whereas, according to the present invention, the cutting edge of the saw tooth, i.e. the portion to be positioned and ground, is sensed. The object of the present invention is to obviate the above inconveniences and provide an improved, fully auto¬ matic grinding machine.

This object is achieved by means of a grinding machine of the type stated in the introduction to this specification and with the distinctive features stated in the appended claims.

One advantage of the invention is that the grinding machine functions regardless of the type or size of the chain mounted for grinding. Thus, no manual adjustments are needed between the grinding of two different types of chains. According to the present invention, the grinding machine comprises a first sensor for sensing the length of the chain, so that the number of saw teeth on the chain can be automatically determined.

Another advantage is that a desired filing angle can be simulated because the grinding motor and the associated grinding wheel are stationary, and because the chain and the unit on which the chain is stretched are pivotably arrange .

Yet another advantage is that no additional devices for locking the chain in the grinding position are requi¬ red. This is due to the fact that the saw chain is fed by means of a motor, unlike saw chains in other grinding machines where the feeding is achieved by means of air cylinders.

According to the present invention, the grinding machine also has a second sensor for sensing the cutting portion of the saw teeth, which makes it possible to program a desired grinding both as to the amount ground off and as to left-hand or right-hand tooth. It is very important that the cutting edge of the saw tooth is sensed, since it is this edge which is to be worked and thus placed in the grinding position, no matter how worn it is. Other types of grinding machines can only distinguish between right-hand and left-hand saw teeth and thus do not sense the cutting portion of these teeth. The invention will be described in more detail below, reference being had to the accompanying drawings illustra¬ ting a preferred embodiment of the grinding machine accor¬ ding to the invention. ' In the drawings,

Fig 1 is a front view of the grinding machine at rest,

Fig 2 is an oblique front view of the grinding machine in operating position, Fig 3 is an enlarged view of a component part of the grinding machine, and

Fig 4 is en enlarged view of a component part of the grinding machine.

Fig 1 shows a saw chain 1 which has been passed over a feeding wheel 2 driven by a motor (not shown). A tensio¬ ning roller 3, which is mounted on a vertically adjustable tensioner 4, is shown in its position of rest. A first sensor 5 for measuring the length of the saw chain is mounted along the tensioner 4. The first sensor 5 consists of a number of limit transducers which are positioned at predetermined distances from one another along the path of displacement of the tensioning roller 3. Since all the saw chains available on the market are standardised such that a certain length corresponds to a certain pitch and, consequently, a certain number of saw teeth, this standard information can be programmed in advance into a computer unit. Once the length of the saw chain has been establi¬ shed by the sensor, information about the pitch and the theoretical number of saw teeth of the chain is thus auto- matically obtained from the computer unit.

An arm 7 rests on the saw chain 1. On the arm 7 is mounted a second sensor 8 which senses the cutting por¬ tions and, via a computer (not shown), supplies a signal to a motor associated with a grinding wheel 10, when grinding is to begin. The entire unit comprising the motor 9 and the grinding wheel 10 is displaceable obliquely downwards in a uniaxial direction towards the saw chain. Fig 2 shows the saw chain 1 in its tensioned state brought about by the tensioning roller 3 of the vertically adjustable tensioner 4.

Fig 3 is an enlarged view of the feeding wheel 2 carrying the saw chain 1, and the arm 7 with the sensor 8. As shown in Fig 4, the sensor 8 comprises four trans¬ ducers 11 arranged in two parallel pairs on the underside of the arm 7. When the rear cutting portion 12 of the saw tooth reaches the rear transducer of one pair (as seen in the direction of motion of the saw chain 1, i.e. anti¬ clockwise), the sensor 8 is activated and transmits to a computer information about whether the next tooth to be cut is right-hand or left-hand. The distance between the transducers of each pair is larger than the length of the front portion 13, the so-called depth gauge, of the saw tooth, but smaller than the length of the rear cutting portion 12 of said tooth. This means that the sensor 8 can sense the portion 12, especially its front cutting edge which is to be ground, so as to control the feeding thereof and the movement of the grinding wheel 10 to the grinding position.

Several of the above-mentioned grinding machine components form part of a so-called pivotable unit. This unit comprises a shaft which is connected to the grinding machine and on which a plate is mounted. The feeding wheel 2, the driving motor and the arm 7 with the sensor 8 are arranged on the upper side of said plate. The upper por¬ tion of the pivotable unit is turnable by means of a piston and cylinder unit connected to the underside of the plate for turning said upper portion, about the shaft arranged in the vertical direction of the grinding machine, through an angle which is determined by the desired alignment between the grinding wheel 10 and the saw chain 1 on the feeding wheel 2. The lower portion of the pivotable unit comprises the tensioner 4 which preferably is an air cylinder that is vertically displaceable on a piston rod mounted on the grinding machine. The tensioning roller 3 is mounted on the tensioner 4 and adapted to be displaced downwardly, thereby to tension the saw chain 1 and keep it tensioned both during feeding and during grinding. The tensioner 4 is also turnable about the piston rod. Since the saw chain 1 serves to connect the upper portion and the lower por¬ tion of the pivotable unit, both portions pivot together with the saw chain 1 when shifting from the grinding of a left-hand tooth to the grinding of a right-hand tooth, or vice versa.

The grinding machine according to the invention operates as follows.

A saw chain 1 to be ground is positioned on the feeding wheel 2. Then, the grinding machine is switched on, and the tensioning roller 3 mounted on the tensioner 4 is displaced downwardly to engage and tension the saw chain 1. Since the feeding wheel 2 is driven by a motor, the saw chain can be tensioned to such an extent that no additional locking of the chain in the grinding position is needed. By means of the first sensor mounted adjacent to the tensioner 4, the length of the saw chain 1 is measured. Then, the computer unit compares the measured length with the programmed standard information and determines the theoretical number of saw teeth on the saw chain 1.

At the same time as the saw chain 1 is tensioned, the arm 7 with the sensor 8 is lowered down onto the upper portion of the tensioned saw chain 1, and a direct-current motor starts the feeding of the saw chain 1. When one pair of the_transducers 11 mounted on the arm 7 has registered the passing of the cutting portion of a saw tooth, a high¬ speed counter in the computer begins to count down a pro¬ grammed number of pulses from a pulse generator on the direct-current motor. At this point, the saw tooth is in the grinding position. Depending on whether the tooth is right-hand or left-hand, the saw chain 1, together with the entire pivotable unit of which it forms a part, is pivoted to the desired position.

Then, the grinding wheel 10 is lowered obliquely downwards to engage the saw tooth and grinds the cutting edge thereof for as long as is necessary, whereupon it returns to the initial position.

The above procedure is repeated, including, if necessary, the shifting between left-hand and right-hand teeth, until the theoretical number of saw teeth pro¬ grammed by the sensor 5 of the tensioner 4 have been ground. However, the theoretical number of saw teeth does not always agree with the actual number. If one or more teeth on the saw chain are missing, a new grinding run starts and the corresponding numbers of saw teeth are ground anew. In actual practice, however, the grinding of such defect saw chains is of no interest. When all the saw teeth have been ground, the tensioning roller 3 returns to its initial position. By means of a so-called pick-up robot, the ground saw chain 1 may then be removed and replaced by another chain which, regardless of type and size, can be fully automatically ground by the grinding machine according to the invention.

If the saw chain 1 at issue is so severely damaged that a considerably amount of metal has to be ground off, the number of saw teeth to be ground can be doubled, trebled or quadrupled by means of a selector button. The saw chain 1, which moves anticlockwise in the grinding machine, will then make two, three or four runs.

Claims

1. A grinding machine for grinding endless saw chains (1) with left-hand and right-hand saw teeth, comprising a feeding wheel (2) adapted to take up a saw chain (1) for feeding the teeth thereof to a grinding position, and a grinding wheel (10) which, in said grinding position, is engageable with a saw tooth for grinding the cutting edge thereof, c h a r a c t e r i s e d by a tensioning means (3) displaceable away from said feeding wheel (2) to engage the saw chain (1) and keep it tensioned on the feeding wheel both during feeding and during grinding; a first sensor (5) adjacent to said tensioning means (3) for sensing the displacement thereof and thus deter¬ mining the length of the saw chain (1); a computer unit which is preprogrammed with informa¬ tion about the length, pitch, and number of saw teeth of standard saw chains, for determining the theoretical number of saw teeth of the saw chain (1) to be ground, said theoretical number serving to determine the total length of feed of the feeding wheel during grinding of the saw chain (1); and a second sensor (8) adjacent to said feeding wheel (2) for sensing the passing of the cutting edge of the cutting portion (12) of the saw teeth while the saw chain (1) is advanced by the feeding wheel (2), this sensing serving to control, by means of said computer unit, the feeding of the cutting edge of the saw tooth and the movement of said grinding wheel (10) to the grinding position.

2. Grinding machine as claimed in claim 1, c h a ¬ r a c t e r i s e d in that said first sensor (5) con- sists of a niαmber of limit transducers which are posi¬ tioned at predetermined distances from one another along the path of displacement of the tensioning means (3).

3. Grinding machine as claimed in claim 1, c h a ¬ r a c t e r i s e d in that the second sensor (8) com¬ prises four transducers (11) arranged in two parallel pairs, the transducers of each pair succeeding one another in the direction of feed of the saw chain (1).