WO1999012410A1

WO1999012410A1 - A device for operating a machining apparatus

Info

Publication number: WO1999012410A1
Application number: PCT/SE1998/001596
Authority: WO
Inventors: Rolf Modd
Original assignee: Rolf Modd
Priority date: 1997-09-09
Filing date: 1998-09-09
Publication date: 1999-03-18
Also published as: SE9703236D0; SE9703236L

Abstract

A device for operating a machining apparatus, the device comprising an engine (1) for operating a machine member, the machining member being arranged on a carrier, means (2) for moving the carrier in relation to an object intended for being machined, and an arrangement (3) for controlling the speed of the carrier moved by the movement means (2), the control arrangement (3) being adapted to relate the carrier speed to a resistance caused by the object. The control arrangement (3) comprises a means (4) for sensing the pressure of a fluid in a conduit (5) connected to an inlet side of the engine (1), and the control arrangement (3) is arranged to control the carrier speed as a function of the sensed pressure.

Description

A DEVICE FOR OPERATING A MACHINING APPARATUS

FIELD OF THE INVENTION AND PRIOR ART

The present invention is related to a device for operating a machining apparatus according to the preamble of claim 1 .

The inventive device will below be described and illustrated for operating a sawing apparatus. The device is especially suitable for operating such a sawing apparatus, but may advantageously be applied to other apparatuses, such as a milling apparatus. The description below, in which the inventive device is applied to a sawing apparatus, is only exemplifying and thereby not in any way limiting.

Previously, it was very difficult to saw off a log in such a way that the saw sword did not get jammed in the log and that the log parts obtained after the log was sawn off did not have any crack formations. A saw chain arranged on a saw sword of a sawing apparatus is driven by an engine of the device. A resist- ance against the movement of the saw sword through the log is caused by the log and increases as the saw sword is moved from a periphery of the log towards the inner parts of the log. This resistance will have a negative effect on the movement of the saw chain and may increase to such an extent that the saw chain will be stopped, and the sawing operation interrupted, by too fast a movement of the saw sword through the log. It is thereby important to move the saw sword relatively slowly through the portions of the log having the largest diameter and thereby causing a large resistance. There is, however, a risk for breaking the log before the saw sword has been moved through the complete log, if the saw sword, on the other hand, is being moved too slowly through the log, which may result in crack formations in the log parts. Such crack formations may extend a long distance in the cut log parts and might result in the respective log parts being at least partly useless and thereby causing large financial losses.

This problem is preferably solved by the saw sword being moved with a speed through the log relating to the resistance caused by the log. The saw sword should thereby be moved relatively fast at the beginning of the sawing operation and thereafter gradually be slowed down towards the inner portions of the log. The speed of the saw sword should be increased as soon as the saw sword has passed the inner portions of the log.

The above mentioned problem is, according to prior art, for example solved by a device, where a first conduit from the outlet side of the sawing engine is connected to the means for moving the saw sword, said means often being formed by a hydraulic cylinder. A further, second conduit is connected by a first end thereof to the first conduit between the outlet side of the engine and the hydraulic cylinder. The second conduit is further being connected with a second end thereof to a reservoir. A throttle member is further arranged on the second conduit between the connection point of the first and the second conduit and the reservoir.

The hydraulic cylinder moves the saw sword through a log with a speed which, according to the known device, is controlled through the resistance caused by the log becoming so large that the engine has difficulties driving the saw member around. This leads to the number of revolutions of the engine being lowered, resulting in a reduced flow of oil through the sawing engine, which causes a lower pressure on the outlet side of the engine. This leads to a lower pressure on the hydraulic cylinder, and thereby to a smaller force, so-called clamp force, with which the hydraulic cylinder affects the saw sword due to the outlet side of the engine being connected to the hydraulic cylinder via the first conduit. This leads to the saw sword being moved with a lower speed. The speed of the saw sword is thereby controlled hydraulically.

There are a plurality of disadvantages with such a device for solving the above mentioned problem. One disadvantage is that heat is generated when a large flow passes through the throttle member, resulting in fans being needed for removing that heat. Such a loss of heat is especially observable in a hot environment. The viscosity of the oil depends on its temperature, i.e. the viscosity is higher when the oil is cold. A flow of cold oil in the conduits is to a larger extent obstructed, especially through the throttle member. This implies that the pressure in the second, further conduit on the engine side of the throttle member becomes large. The engine powers the saw chain with an effect depending on the pressure difference between its inlet and outlet sides. The pressure of the oil is large on the engine side of the throttle member when a cold oil is used and, thereby, the pressure also at the outlet side of the engine is large. This implies that said pressure difference between the inlet and outlet sides of the engine becomes relatively small, which results in a low engine effect. A further disadvantage with the known device is that the hydraulic cylinder responds relatively slowly to changes in the resistance caused by the log due to the hydraulic control of the same.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for operating a machining apparatus, which eliminates the above mentioned disadvantages when machining an object by means of a machining member arranged on a carrier.

This object is achieved by means of the inventive device by the fact that the control arrangement comprises a means for sensing the pressure of a fluid in a conduit connected to an inlet side of the engine, and that the control arrangement is adapted to control the carrier speed as a function of the sensed pressure.

According to one embodiment of the invention, the machining member is formed by a saw member. This implies that the invention solves a plurality of the problems arising when sawing is performed with a sawing apparatus according to prior art.

The control arrangement comprises a means for controlling the carrier speed, which is formed by a proportional valve, according to a further embodiment of the invention. This implies that the movement means affects the carrier with a force, which is possible to increase or decrease fast, responding to pressure changes of the fluid in the conduit connected to the inlet side of the engine.

BRIEF DESCRIPTION OF THE DRAWING

With reference to the enclosed drawing, a more close description of preferred embodiments of the invention follows here- under.

Figure 1 illustrates a principal drawing of the inventive device according to a first preferred embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 illustrates a principal drawing of a connection diagram according to a first preferred embodiment of the inventive device. The device comprises an engine 1 for operating a machining member. The machining member is arranged on a carrier. A means 2 for moving the carrier in relation to an object intended for being machined is also arranged. The device also comprises a control arrangement 3 for controlling the speed of the carrier as the latter is moved by the movement means 2. The control arrangement 3 is arranged to relate the carrier speed to a resistance caused by the object. The control arrangement 3 comprises a means 4 for sensing a pressure of a fluid in a conduit 5 connected between the pump and the engine 1 on an inlet side thereof. The control arrangement 3 is arranged to control the carrier speed as a function of the sensed pressure. The letter notations P and T indicates "Pump" and "Reservoir", respectively.

The invention will below be described as being connected to a sawing apparatus. Such a sawing apparatus may be arranged both for felling a tree and removing the branches therefrom, as well as for sawing off a log arranged in a preferably horizontal direction.

The engine 1 and the means 2 for moving the carrier are preferably powered hydraulically by a pump, which is powered by a diesel engine. Said pump also supplies other units in the sawing apparatus, such as feeding rolls, with a pressurised fluid. The part of the hydraulic system forming the inventive device is activated by an on/off-valve 6. The on/off-valve 6 is controlled by a central processing unit 7 comprised in the control arrangement 3. A fluid is forced through the conduit 5 when the valve 6 is activated and the engine 1 starts to rotate. The engine 1 powers a machining member via an engine axis 8. The machining member is formed by a saw member, which is preferably formed by a saw chain, when sawing is performed. The saw member may, however, within the frame of the inventive claims also be formed by, for example, a saw belt. The saw member is driven by the engine 1 via the engine axis 8 in relation to the carrier having the saw member arranged thereon. The carrier is preferably formed by a saw sword. The saw member (saw chain) is preferably arranged to execute a rotating movement. An outlet side of the engine 1 is connected to a reservoir 9. The control arrangement 3 comprises a means 10 for controlling the fluid fed to the movement means 2. The control means 10 is therefore connected to the central processing unit 7. It is possible to control both the direction of the carrier and the force applied to the carrier by means of the movement means.

The movement means 2 is suitably formed by a hydraulic cylinder in a hydraulic system. The flow fed to the hydraulic cylinder is controlled by the control means 10. When the hydraulic cylinder 2, which in this case is formed by a double- acting cylinder, is supplied with a large flow, the force with which the fluid affects a piston 1 1 in the hydraulic cylinder 2 is increased. A rod piston 12 connected with a first end thereof to the piston 1 1 is adapted to be connected to the carrier at a second end thereof. The force applied to the carrier is increased, and the speed thereof is also increased when the force acting on the piston 1 1 is increased.

Via the hydraulic cylinder, the saw sword is brought to carry out a movement towards an object to be sawn, for example a tree log, while the saw chain is rotating. A resistance caused by the log against the movements of the saw sword and the saw chain arises when the saw sword reaches the log. This resistance increases when the saw sword is moved towards the portion of the log having the largest diameter, whereafter the resistance is gradually decreased, when the saw sword is moved from said central portion through the remaining part of the log. The engine 1 rotates the saw chain with a lower speed when the resistance against the movement of the saw chain is increased, wherein the pressure on an inlet side of the engine increases. The speed of the saw sword must thereby be reduced in order to avoid the resistance against the movement of the saw chain from becoming large enough to stop the rotation of the saw chain. This pro- blem is, according to the inventive device, solved by the fact that the sensing means 4 senses the pressure in the fluid in the conduit 5 connected to the engine 1 on an inlet side thereof, and sends a signal to the central processing unit 7, which reduces the force applied to the saw sword by the movement means 2 via the control means 10. The speed of the saw sword is thereby reduced.

The speed of the saw sword should gradually be increased when the remaining parts of the log from the central portion of the log to the periphery of the log are sawn, in order to avoid that the log is broken off before the saw sword has moved through the complete log, which could result in crack formations. The device also solves this problem due to the fact that the pressure in the conduit 5 on the inlet side of the engine 1 is reduced when the saw sword has passed the central portion of the log. The pressure sensing means 4 thereby senses the reduced pressure and the hydraulic cylinder 2 is brought to increase the saw sword speed via the central processing unit 7 and the control means 10.

The control arrangement 3 will control the carrier speed inversely proportional to the pressure sensed by the pressure sensing means 4, i.e. increase the carrier speed when the sensed pressure is reduced and reduce the carrier speed when the sensed pressure is increased.

By the inventive device, where there is an electrical control of the force applied to the carrier, and thereby the speed thereof, via the pressure sensing means 4, the central processing unit 7 and the control means 10, it is implied that fast changes of the carrier speed responding to the pressure sensed by the pressure sensing means may be accomplished.

Conventional sawing apparatuses are arranged with gripping arms, which grip around a log intended for being sawn off. These gripping arms are provided with sensors for measuring the thickness of the log. The control arrangement 3 may control the saw sword in such a way that it is only moved through the complete log, but not further in the same direction, by connecting these sensors to the central processing unit 7 of the inventive device. This is advantageous when a log of a growing tree is to be sawn off, due to the fact that there is a risk that the saw sword otherwise is being forced through the log to a position on a side of the log opposite the starting position, which could lead to the log falling onto the saw sword when the tree is falling. This could, in turn, result in the saw sword being de- formed. It is, according to the inventive device, thereby possible to stop the saw sword and move it back along the same path as when the log was being sawn off just when the saw sword has sawn through the log in order to finally reach a position substantially corresponding to the starting position.

After felling a tree and removing the branches therefrom, the remaining log is, according to prior art, preferably positioned in a horizontal direction in order to thereafter be sawn off into suitable lengths. The inventive moving means 2 is preferably controlled so that the saw sword is brought to perform a fast return motion after the saw sword having sawn through a log.

It is, due to the sensible control of the speed of the saw sword, possible to saw off very thick, as well as very thin, logs by means of the inventive device.

At tree harvesting, trees are felled by sawing, the branches are removed from the trees, and the tree logs are sawn to log parts in suitable lengths. The log has a continuously reducing cross- section area from the root of the tree to the top of the tree. Wood of different dimensions is therefore sawn during tree harvesting.

The force acting against the movement of the saw sword will increase when the saw sword is moved through the object from its periphery to its centre and decrease when the saw sword is moved through the object from its centre to its periphery, when an object in the form of a log or branch is sawn, due to the substantially circular cross-sectional surface of the latter. The maximum force counteracting the movement of the saw sword will thereby be different for different dimensions of the cross-section area.

A minimum effect is used during the sawing operation due to the fact that the control arrangement 3 is arranged to substantially continuously decrease the carrier speed when the pressure sensed by the pressure sensing means increases and substantially continuously increase the carrier speed when the pressure sensed by the pressure sensing means is reduced. An optimum operation from the effect point of view is thereby achieved independent of the dimension of the object to be sawn off.

For a certain cross-section size, one type of trees may further have different maximum forces acting against the movement of the saw sword depending on, for example, if it is frozen or non- frozen, sap content, the position in the longitudinal direction of the log, by which the sawing is to take place etc. The material has a higher water content during sap time, which implies that the force counteracting the movement of the saw sword is smaller than during non-sap time. The high water content im- plies that the log is heavier, and it is therefore especially important to achieve a fast sawing operation by sawing a horizontally positioned log in order to counteract crack formations.

The force counteracting the movement of the saw sword is larger in the lower parts of the log due to the fact that the roots of the tree extend up in the log in these parts.

Thus, there are a plurality of parameters determining the force counteracting the movement of the saw sword through an object in the form of a log. An optimum sawing operation regarding output and crack formation counteraction is achieved by means of the inventive device thanks to said substantially continuous change of carrier speed as a function of the pressure sensed by the pressure sensing means.

The substantially continuous change of the carrier speed is preferably controlled analogously, resulting in a stepless change of the carrier speed. A digital control of the carrier speed is, however, also within the frame of the inventive claims, said digital control implying a stepwise change, but however, with so small step sizes that the carrier speed is substantially continuously changed.

The function for controlling the carrier speed depending on the pressure sensed by the pressure sensing means 4 of the control arrangement 3 is set with reference to performance characteristics of the system in question. The system performance characteristics are in this case related to the pump size, the engine size, and the design of the hydraulic system, especially the design of the conduit 5. A certain fall of pressure is present between the pump and the engine, due to, for example, the design of the conduit, the length thereof, and bendings thereof, which is considered by said setting. A regulation of the function for different applications, such as various wood types, is therefore not needed, but the function is only depending on said system performance characteristics.

The means 10 for controlling the carrier speed may also within the frame of the inventive claims be arranged to control the direction of the carrier. A proportional directional valve is an example of such a means, providing control of both the direction and the flow.

It should be noted that the embodiment discussed above and illustrated in the drawings only should be regarded as an example. The invention may thus be realised in other ways within the frame of the inventive concept. It is especially noted that men skilled in the art after having been presented to the inventive concept, of course, are capable of carrying out different formings of the exemplified embodiment without leaving the scope of the inventive claims.

Claims

1 . A device for operating a machining apparatus, the device comprising an engine (1 ) for operating a machining member, the machining member being arranged on a carrier, a means (2) for moving the carrier in relation to an object intended for being machined, and an arrangement (3) for controlling the speed of the carrier moved by the movement means (2), the control arrangement (3) being adapted to relate the carrier speed to a resistance caused by the object, characterised in that the control arrangement (3) comprises a means (4) for sensing the pressure of a fluid in a conduit (5) connected to an inlet side of the engine (1 ) and that the control arrangement (3) is adapted to control the carrier speed as a function of the sensed pressure.

2. A device according to claim 1 , characterised in that the machining member is formed by a saw member.

3. A device according to claim 2, characterised in that the saw member is formed by a saw chain.

4. A device according to any of the preceding claims, characterised in that the carrier is formed by a saw sword.

5. A device according to any of the preceding claims, characterised in that the movement means (2) is formed by a hydraulic cylinder.

6. A device according to any of the preceding claims, characterised in that the control arrangement (3) comprises a central processing unit (7) and a means (10) for controlling the carrier speed, which is connected to the central processing unit (7), and that the pressure sensing means (4) is connected to the central processing unit (7).

7. A device according to any of the preceding claims, characterised in that the means (10) for controlling the carrier speed also controls the direction of the carrier.

8. A device according to claim 7, characterised in that the means (10) for controlling the carrier speed is formed by a proportional valve.

9. A device according to any of the preceding claims, characterised in that the control arrangement (3) controls the carrier speed inversely proportional to the pressure sensed by the pressure sensing means (4).

10. A device according to any of the preceding claims and claim 6, characterised in that the means (10) for controlling the carrier speed is adapted for being controlled electrically by the central processing unit (7).

1 1. A device according to any of the preceding claims, characterised in that the control arrangement (3) is adapted to substantially continuously lower the carrier speed as the pressure sensed by the pressure sensing means (4) increases and substantially continuously increase the carrier speed as the pressure sensed by the pressure sensing means is being re- duced.

12. A device according to claim 1 1 , characterised in that the substantially continuously lowering and increase, respectively, of the carrier speed is stepless.

13. A device according to any of the preceding claims, characterised in that the function, with which the control arrangement (3) controls the carrier speed depending on the pressure sensed by the pressure sensing means (4), is set based on the performance characteristics of the pump, the engine (1 ), and the conduit (5).