METHOD AND ARRANGEMENT FOR MONITORING THE WORKING MOVEMENT OF A DEVICE OPERATED BY A HYDRAULIC CYLINDER

Abstract: The invention relates to a method and system for following accurately the working motion of an apparatus powered by a hydraulic cylinder such as the working motion of the cutting saw of a harvester as well as predicitng accurately and reliably the ending time of the working motion. The invention may be applied e.g. for timing the colour marking of cut logs as well as halting the saw at the end point of the working motion. It is characteristic that the oil withdrawing from the hydraulic cylinder during the working motion is conducted into a hydraulic motor (30). The rotations or partial rotations of the hydraulic motor (30) are registered as electric pulses with an inductive transducer (24) or the like device.

Description: METHOD AND ARRANGEMENT FOR MONITORING THE WORKING MOVEMENT OF A DEVICE OPERATED BY A HYDRAULIC CYLINDER The invention relates to a method and system for following the working motion of an apparatus powered by a hydraulic cylinder such as following the working motion of the cross-cutting saw of a harvester and/or calculating the moment of reaching the extreme point of the working motion. Patent publications US 4491163, FI 67288, FI 60805, and 91588 describe various kinds of loading harvesters. According to the prior art technique besides felling and cutting a harvester performs also measuring the amount of felled trees and colour marking of the cut logs. Both measuring and colour marking are far automatic operations. Measurement of the log diameter is performed with sensors placed in connection with the articulated shafts of the capstan arms so that the said sensors register the turning of the arms about their axes caused by the change in the log diameter. The sensors communicate with a programmed computer which calculates the diameter. Based on the measured diameter and tapering of the trunk the computer calculates beforehand the diameter at the next cutting point. According to the known technique the cut logs are marked with different colour codes depending on the diameter so as to facilitate sorting. Colour marking is done so that the colour chosen according to the diameter of the log is sprayed through a nozzle onto the end of a newly cut falling log on the very instant the log is still in air. Colour marking is described e.g. in the patent application FI 885958. The colour nozzles may be placed just at the tip of the grab as depicted in the patent application. The sensor registering the working motion of the saw sends the computer the information of how far the cutting stage has proceeded. From this information and knowledge about the diameter the computer is able to predict the moment when the log will be cut. The computer sends signal to a magnetic or electro-hydraulic valve which in turn controls dispensing of the colour to one or more nozzles so that spraying takes place just at the right moment. Figs 1-2C outlines the prior art method of registering the motion of a cutting saw. The cutting saw is normally attached to the side beam of the harvester mainframe with an articulation. Fig. 1 shows a cutting saw 10 seen from the direction of a tree trunk 50. The saw is powered by a hydraulic cylinder not shown in the figure. The working motion of the saw is its turning motion from point kl, where the cutting blade 11 touches the upper surface of the trunk 50, to point k2, where cutting has just been completed. The total working motion of the saw is the turning angle marked with the letter K. The total working motion K needed for the cutting is known in advance because a computer has calculated the diameter at the cutting point. The starting point kl of the working motion is always approximately the same independent of the thickness of the tree trunk but its end point k2 always varies according to the diameter of the tree trunk. Location kx of the cutting saw during the working motion is followed with a motion sensor. A part 20 belonging to the motion sensor, which is explained in greater detail in the following, is attached to the body 12 moving with the saw. The computer calculates how much time the motion kl- kx has required and is able to predict the moment at which the saw has reached the point k2 in other words when its whole working motion K has been completed. According to a known solution the arrangement shown in Fig. 2A is used as the motion sensor for a cutting saw. A steel bow 20 provided with holes 21 is fastened to the body which moves with the saw. The head of an inductive transducer 24, which is placed so as to remain stationary during the saw movement, is perpendicular to the surface of the steel bow 20 (Fig. 2 B) . A solid hood which protects the saw from the sides and above is not shown in Figs. 1 and 2. The inductive transducer is suitably attached to the said protective hood. When the bow 20 moves past the stationary transducer 24, the magnetic field which the transducer registers will vary depending on whether it faces a metallic region 22 or hole 21 of the steel bow. Each change in the magnetic field generates an electric pulse in the inductive transducer. The sum p of the electric pulses from the beginning of the working motion is calculated in the computer and it is compared with the number of pulses P required for the total working motion. Thus the ratio p/P is the measure of how far the motion has proceeded. To be able to calculate in practice the cutting moment more accurately using the above described steel bow two inductive transducers 24 and 24' in parallel have been adopted (Fig. 2 C). The distance between the transducers has been chosen so that the first transducer 24 always senses a metallic region 22 while the other transducer 24' senses a hole 21 and vice versa. In this way each hole 21 can be counted twice during the working motion of the saw i.e. the number of pulses obtained is doubled which naturally increases accuracy in predicting the end point of the working motion. However, in practice the above described motion sensor based on the mechanically fastened steel bow involves several problems. In order to function properly it is important that the distance between the head of the transducer and the steel bow remains accurately unchanged and about 1 mm. This is difficult to guarantee in conditions where the harvester operates. The device is continuously exposed to mechanical knocks, dirt and changes in weather which cause damage. This results in faulty signals leading to calculation errors concerning terminal point of time of cutting. This in turn leads to insufficient colour marking because the colour is sprayed from the nozzle too early or too late. Another problem with the above described motion sensor is its unsatisfactory accuracy which is due to low number of signals. Although one uses the system of two sensors of Fig. 2C, the number of signals remains too low. Very accurate calculation of the terminal point of time of sawing would require a higher number of signals. The objective of this invention is to remove the above problems and provide a new method and system which allows very accurate following of the working motion of the cutting saw of a harvester or any other apparatus powered by a hydraulic cylinder as well as prediction of the terminal point of time of the working motion with high accuracy. The characteristics of the invention appear in claims 1 and 5. The method according to the invention is characterized in that the amount of oil withdrawing from the hydraulic cylinder during a working motion is conducted into the hydraulic motor and the rotations or partial rotations performed by the hydraulic motor are registered as electric pulses with an inductive transducer or the like device. The system according to the invention is characterized in that it comprises a hydraulic motor into which the amount of oil withdrawing from the hydraulic cylinder during a working motion is conducted. The rotations or partial rotations of a part coupled to the shaft of the hydraulic motor are counted with the inductive transducer or the like device of the system and transformed into electric pulses . The invention will be explained in the following referring to the enclosed drawings in which Fig. 1 shows the cutting saw of a harvester and its working motion, Figs 2A-2C show a prior art motion sensor, Fig. 3 shows schematically the system according to the invention, Fig. 4 shows an end view of a part relating to the system of Fig. 3 according to one embodiment, and Fig. 5 shows a detail of the longitudinal section of a sleeve relating to the system of Fig. 3. Fig. 3 shows the system according to the invention as separate parts . During the working motion K of the cutting saw a certain amount of oil withdraws from the hydraulic cylinder. A corresponding amount of oil is conducted through a hydraulic motor 30. The hydraulic motor need not be placed in the immediate vicinity of the hydraulic cylinder but it may be disposed in a suitable place at a distance apart. When the cutting saw starts its motion at point kl (Fig. 1), feeding of oil into the hydraulic motor starts. A part 32 is attached to the shaft 31 of the hydraulic motor 30 so that it rotates along with the shaft. In one embodiment this part is a cylindrical body made of metal or metal alloy which affects the magnetic field which is registered by an inductive transducer. Its cross-section is shown in Fig. 4. As seen in the figure the cross-section is a circle with two segments removed. A sleeve 34 is fitted round the part 32. The jacket of the sleeve 34 has a hole 35 (see Fig. 5) for the inductive transducer 24. The inductive transducer is fastened so that an accurate predeterminate distance remains between its end 25 and the curved circumference 33 of the part 32. The reference number 36 denotes the fastening nut. When the part 32 fitted to the shaft 31 according to Fig. 4 performs a rotation, it will in each rotation change twice the magnetic field registered by the inductive transducer 24. The inductive transducer transforms these changes in the magnetic field into electric pulses . By selecting a hydraulic motor with a rotational volume of 8 cm and a part 32 shown in Fig. 4 one gets 48 electric pulses during the cutting motion of the saw if the diameter of the cut trunk is 60 cm. The prior art system of Fig. 2C gives only 34 pulses with the same trunk diameter. The system according to the invention therefore gives a significantly higher number of pulses from the working motion of the saw, which in turn means that the end point can be predicted with greater accuracy. An even higher number of pulses from each rotation of the hydraulic motor would be obtained, if necessary, by using such a part 32 that has three or more segments cut off. Alternatively, one could use a hydraulic motor with a smaller rotational volume. However, the above mentioned number of pulses is sufficient to control the cutting saw of a harvester. The part 32 need not necessarily be made of a magnetic material. One could as well use a part made of some non¬ magnetic material and embed separate pieces of permanent magnets in contact with the jacket of the part. Naturally other devices than the above described inductive transducer may be used for counting the rotations or partial rotations of the hydraulic motor. Such a device is, for example, a pulse transducer based on a photocell or any device operating like an on/off switch. The system of the invention is not apt to damages making its operation reliable. The exact termination point determined by the method of the invention may be used for a more accurate timing of colour marking. The moment can be accurately calculated at which the cut log in its dropping course has passed the tree trunk in the grab of the harvester, and at which a marking or treating agent is sprayed onto the end of the cut log . The invention may be also applied for timing the distribution of some treating agent like urea. Another application is the automatic halting of the cutting saw right after cutting. In present harvesters the saw continues its motion beyond the extreme point k2 of its working motion (Fig. 1). This unnecessary idle running takes time. Halting of the cutting saw after the end of the working motion speeds up the operation of a harvester and facilitates its control. Although the above description concerns the cutting saw of a harvester, it is obvious that the invention may be applied in any apparatus which performs a repeated working motion and which is powered by a hydraulic cylinder. It is obvious to the specialist in the field that various embodiments may vary within the scope of the enclosed claims.

Claims: CLAIMS 1. Method for determining the position of an apparatus powered by a hydraulic cylinder while it is performing a repeated working motion and/or calculating the moment at which it reaches the extreme point (k2) of the working motion, wherein - progress of the motion is registered with an inductive transducer (24) or the like device transforming the performed motion into electric pulses, - the electric pulses registered from the beginning of the working motion are added up by a computer, and - the number p of added electric pulses is compared with the predeterminate total number P of pulses required by a complete working motion, characterised in that - the amount of oil withdrawing from the hydraulic cylinder during the working motion is conducted into a hydraulic motor (30), and - the rotations or partial rotations performed by the hydraulic motor (30) are registered as electric pulses with an inductive transducer (24) or the like device. 2. Method according to claim 1, characterised in that the apparatus performing the working motion is the cutting saw of a harvester and that the complete working motion (K) is the working motion required to cut a tree trunk. 3. Method according to claim 2, characterised in that the change in the ratio p/P is followed and the motion of the cutting saw is halted when p=P, in other words on the instant the tree trunk has been cut. 4. Method according to claim 2 or 3, characterised in that - the change in the ratio p/P as a function of time is followed, - the point of time is calculated at which the cut log in its dropping course has passed the tree trunk in the grab of the harvester, and - a marking or treating agent is directed to the end of the cut log at said point of time. 5. System for determining the position of an apparatus powered by a hydraulic cylinder while it is performing a repeated working motion and/or calculating the moment at which it reaches the extreme point (k2) of the working motion, the system comprising means for determining the complete working motion, an inductive transducer (24) or the like device for following the motion of the work- performing apparatus during a working stage, and a computer, characterised in that -the system comprises a hydraulic motor (30) into which the oil withdrawing from the hydraulic cylinder during the working motion is conducted, - the rotations or parts of rotations of a part (32) coupled to the shaft (31) of the hydraulic motor (30) are counted with the inductive transducer (24) or the like device of the system and transformed into electric pulses. 6. System according to claim 5, characterised in that in each rotation the part (32) changes once or more often the magnetic field registered by the inductive transducer (24) placed in the vicinity of the part (32), the inductive transducer transforming the changes in the magnetic field into electric pulse. 7. System according to claim 5 or 6, characterised in that the part (32) coupled to the shaft of the hydraulic motor is a cylindrical part (32) made of metal or metal alloy from which one or more cylinder segments have been removed, and that a sleeve (34) has been fitted round the part (32), and that the sleeve jacket has a hole (35) for the inductive transducer. 8. System according to claim 5, 6, or 7, characterised in that the apparatus performing the working motion is the cutting saw of a harvester and that the complete working motion (K) is the working motion required to cut a tree trunk. 9. System according to claim 8, characterised in that it comprises control means for halting the motion of the cutting saw on the instant the tree trunk has been cut. 10. System according to claim 8 or 9 , characterised in that it comprises control means for distributing a marking or treating agent onto the end of the cut log at the moment when the cut log in its dropping course has passed the tree trunk in the grab of the harvester. 11. System according to any of the claims 8-10, characterised in that the rotational volume of the 3 hydraulic motor is 8 cm and that the cross-section of the cylindrical part (32) is a circle with two of its opposite segments cut off .

Inventors: LAAKSONEN JARI, TOIVOLA ALPO, LAAKSONEN, JARI, TOIVOLA, ALPO
Applicants: LAAKSONEN JARI, LAKO FOREST OY LTD, TOIVOLA ALPO, LAAKSONEN, JARI, TOIVOLA, ALPO
Application year: 1997
Main classification: F15B15
IPC codes: F15B15