ELECTROHYDRAULIC GUIDE SYSTEM

Abstract: An electrohydraulic governing system for governing system for governing at least movements of objects (3, 4) actuated by pressure fluid, one at the time or several simultaneously, which can receive or deliver energy, wherein the governing desires from an impulse generating guide means (1) via an electronic guide unit (2) are performed provided that this is possible in view of limitations in a pressure fluid source (5) delivering pressure fluid to the objects or provided this can be allowed in view of the strength, life and stability of the machine governed by the guide system or by the objects and as long as the functions operate and as long as the guide system or the guided machine is governed within limited secure field, wherein all the time the volume of the different parts of the sytem filled with pressure medium is measured directly or indirectly and upon governing of the pressure medium source and the valve means (8, 13, 15) connected to respective object it is governed so that the pressure fluid source in each moment always delivers a lower volume flow than the flow that the valve means want to deliver to the objects. Moreover, the system includes position transmitters (7, 12, 14) arranged to measure the position of each object and return the measured values to the guide unit (2).

Description: Electrohydraulic guide system The present invention relates to a method and an apparatus of the kind stated in the preamble part of the claims 1 and 10/ respectively. Modern guide systems and valves governing several objects from a common pressure fluid source are more and more of¬ ten constructed such that they receive a so called load- sensing function. Upon load-sensing it is scanned among the objects being activated and which receive volume flow from supply or pressure conduit out to the object requi- ring the highest pressure. In a fully hydraulic solution this is obtained by using several different back valves. The highest sensed pressure is returned to the pressure fluid source and governsthe source such that it governs out the return pressure plus in addition as much as is required for the valve to be able to govern the volume flow with a pressure drop of usually about 25 bar. Thus, the object requiring the highest pressure is like the other objects loaded by an energy loss unnecessary per se. In electrohydraulic guide systems the highest pressure can be chosen and measured with electric pressure transmitter. Each object must then have at least one transmitter for each force direction, i.e. two transmitters for double- acting cylinders and motors, and also at least one pressure transmitter positioned on the supply conduit from the pres- sure fluid source to the valves of the objects. Since elect¬ ric pressure transmitters are considered to involve high costs and lower reliability than fully hydraulic devices based on back valves the fully hydraulic alternative has up to now been predominant. Load-sensing systems and electrohydraulic systems exist substantially in such cases where the requirements are comparatively high, since the cost for the guide system is higher than for the conventional simpler guide systems which have been predominated up to now. The load-sensing systems have not been developed as rapidly and received the large marked share as many have expected. The explana¬ tion to this is probably that the advantages have not been considered to balance the increased cost. Electrohydraulic guide systems have rapidly been developed and take continuously larger and larger market shares. High demands on automatization, increased supervision and secu¬ rity press on the development towards electrohydraulic systems having positiontransπάtters and ability for position governing. Microprocessors and better transmitters for pres¬ sure and position make today advanced guide technique pos¬ sible as to both function and cost. A relatively rapid and intensive development of the electrohydraulic has, however, mainly been directed towards improvements of the conventio¬ nal hydraulic components and guide principles with electro¬ hydraulic solutions rather than to create new guide prin¬ ciples and components adapted to the completely new con¬ ditions that the access to microprocessors and transmitters provides. The present invention, which accordingly relates to a method and an apparatus for electrohydraulic governing of several objects from a pressure fluid source, makes possible to unite the functions such as load-sensing with a minimum pressure increase, the ability of position gover¬ ning and signal treatment in microprocessors with an eco¬ nomic construction requiring a minimum of transmitters and highly simplified hydraulic components and elements. The invention have not in view to improve old governing prin¬ ciples or components but instead provides a new concept for electrohydraulic with the possibility of governing both position, speed and acceleration. Since the inven¬ tion furthermore provides a flexible system construction, the system can with the aid of electric pressure transmit¬ ters in existing cases also govern pressure, i.e. force or moment. - " ' The characteristics of the invention appear from the claims. Since the invention includes position transmitters and proceeds from that these transmitters are a self-evident condition for an effective, flexible and reliable gover¬ ning system, these transmitters are not possible to elimi¬ nate out of the method or the apparatus but are a condi¬ tion for each satisfactory governing system. Other transmit¬ ters have not the same self-evident position in the governing system. One must of course use certain pressure transmitters for measuring effect, moment, force etc., but these transmitters then have a limited extent. Thus, the present invention provides a method and an apparatus mainly only requiring position transmitters on the objects in order to be able to co-drive the pressure fluid source and the objects without any appreciable up-building of pressure above the pressure that the object having the highest pressure requires. This simple and cost-saving guide system according to the invention requires in order to operate a combination of three measures. Firstly, the position on the objects must be measured and the measure values returned to the electro¬ nic system, which then also can calculate the speed and acceleration of the objects. Secondly, the valves gover- ning each object shall never allow input signal to govern out more than what is possible to realize in view of limi¬ tations of the capacity of the pressure fluid source, i e the volume flow which in every moment can be supplied to the objects via the common supply conduit. Thirdly, the pressure fluid source shall for avoiding up-building of pres¬ sure in every moment be governed such that it delivers to the supply conduit a small quantity less volume flow than the valves of the objects try to govern out from the supp¬ ly conduit to the objects. The valve governing the object having the highest pressure can in such a case not receive the volume flow it strives to govern out. It will then open to a comparatively large extent resulting in a low pressure drop over the valve and low system pressure in the supply conduit. Since position governing presupposes position ransmitters of some kind and since a well operating electrohydraulic guide system normally is constructed such that it only tries to govern out suchmovements that are possible to perform, the¬ se two conditions are normally always met. The governing of the pressure fluid source takes place by means of guide signals of the type increase or decrease. The information to these guide signals arrives from the position transmitter of the objects, i.e. from the information about the posi- • tion, speed and acceleration of the objects. The electro¬ nic system registers and adds thespeeds of each object and registers and adds a test point which is applicable to each object. The pressure fluid source is governed for increase or decrease of its delivered volume flow so that the deli¬ vered volume flow is a small quantity lower than the volume flow which should give all objects the speed that each ob- ject valve strives to govern out. By the present invention a method and and apparatus is provided which lacks parti¬ cular means for pressure-sensing and which instead causes that the object requiring, the highest pressure directly via a comparatively low pressure drop over the valve of the object directly governs the pressure in the SUDPIV con¬ duit. The governing of the object having the highest pres¬ sure requirement will in this manner first-hand to be gover¬ ned by the governing of the pressure fluid source. The valve of the object, however, tries all the time to govern the speed of the object towards the value that the input sig¬ nal indicates, and when the object changes from requiring the highest pressure to some lower pressure, the valve of the object takes over the governing from the pressure fluid source. Thus, in a method and an apparatus according to the invention there are no special devices and thereby components and costs for the almost perfect load-sensing function which is obtained. The function .is realized by the electronic system and by only comparison of real and desired values for the speeds of the different objects. Thus, the cost for the load-sensing co-driving of object and pressure fluid source is very low. In all hydraulic guide systems the speed of the object re¬ quiring the highest pressure decreases when one tries to govern out a larger total volume flow from the supply con¬ duit than what the pressure fluid source can supply to the supply conduit. It is advantageous that the desired speeds of the electronic system is reduced in proportion to their values, so that the total reduced desire all the time only tries to govern out volume flow to the objects lying below or on the limit of the capacity of the pressure fluid source. When hydraulic guide systems are used in connections where the object get stuck or are not able to govern out the de¬ sired volume flow or speed, it is appropriate to limit the input signal to the valve of the object so that the signal never is allowed to be larger than for instance 120% of the object speed calculated via the position transmitter of the object, or for instance minimum a small speed. If the object gets stuck, the system reacts by raising to maximum system pressure. By reducing and adapting the input signal to the actual object speed/ nnecessary energy losses and capacity losses are avoided. The valves guiding the volume flow to and from the objects can be constructed in many ways. Preferably the valves are constructed such that the inlet side can be closed when the volume flow is governed from the object to the return con- duit to tank. Moreover, the governing of the volume flow to and from the object should preferably be formed such that automatically the inlet volume flow will give a higher, for instance 30%, object speed than the return volume flow. Hereby unneeded pressure up-building in the valves of the objects is avoided. The- result of this is that when a load for instance is lifted, i.e. when the object is energy absorbing and operates as a motor, the speed of the valve is governed on" the inlet side, whereby the pressure drop on the outlet side to the return conduit is low, or when for instance a load is lowered, i.e. when the object is energy delivering and operates as a pump, the speed of the valve on the outlet side is governed, wherein with advantage as large part as possible of the inlet volume flow can be delivered from the return conduit via back valves, so called anticavitation valves. In a method and an apparatus according to the invention also pressure and force can of course be governed. An electric transmitter is then arranged on the object on the side where the pressure shall be governed. The valve of the object is now governed such that the inlet side opens and governs the pressure when this shall increase and the outlet side go¬ verns the pressure when this shall decrease. By the fact that the position transmitters of the objects measure the received volume flow to the objects and owing to the fact that via the inlet signals to the object valves it.is with the aid of the electronic guide system possible to determinewhich volume flow that flows from the supply conduit to the objects, the total volume flow flowing from the supply conduit to the objectscan with sufficient accu- racy easily be calculated. If a volume flow meter is in¬ serted after the pressure fluid source in the supply con¬ duit a fast indication can be obtained if the supply con¬ duit should brake or a larger leakage should arise. It is accordingly with the aid of the electronic system possible to obtain an out-pumping protection which automatically and very rapidly closes the pressure fluid source. The invention is in the following described more in details in embodiments with reference to .the accompanying drawing, wherein Fig. 1 schematically shows an apparatus according to the invention with components included in the apparatus, Fig. 2 schematically shows another embodiment of a part of the apparatus according to Fig. 1, and Fig. 3 schematically shows another embodiment of another part of the apparatus according to Fig. 1. The embodiment shown in Fig. 1 includes an outer impulse generating guide means 1 , which for instance is governed by an operator and which delivers desired values to an electronic guide system 2. The guide system 2 governs a number of objects for driving a machine, for instance a crane. Two such objects 3 and 4 are shown in Fig. 1. The guide system 2 also governs a pressure fluid source 5 via an electric set device 6. In the illustrated embodiment the object 3 is of linear type, a hydraulic cylinder, and is provided with a position transmitter 7, for instance a potentiometer, digital transmitter, or another conventional transmitter, and the object 3 is governed by a valve 8 con¬ nected to a pressure or supply conduit 9 from the pressure fluid source 5 and to a return conduit 10 connected to a tank 11. The object 4 is exemplified shown to be of rota¬ ting type and is provided with a position transmitter 12 and is governed by a valve 13 connected to the supply con¬ duit 9 and the return conduit 10. The objects 3, 4 and eventually other objects not shown are connected in parallel to the supply conduit 9 and the return conduit 10. The guide system 2 receives signals about desired movements from the outer guide means 1 and when required reduces the signals for instance proportionally down to such levels that the pressure fluid source can govern out the movements even possibly with lower speed via output signals to the ob¬ jects 3 and 4 governed by the valves 8 and 13. At the same time the guide system 2 via the set device 6 governs the pressure fluid source 5 for feeding to the supply conduit 9 a volume flow being a small quantity lower than the volume flow that the valves 8 and 13 try to govern from the supply conduit 9 to the objects 3 and 4. The governing of the pressure fluid source 5 takes place with the aid of the summing-up of the speeds that can be calculated with the aid of the information "from the position trans¬ mitters 7 and 12 and with the aid of the sum of the in- put signals delivered to the valves 8 and 13. The guide system is constructed such that it is essentially the position transmitters 7 and 12 and the calculations of speed and acceleration that the input signals to both the valves 8 and 13 of the objects 3 and 4 and the set device 6 of the pressure fluid source 5. The valves 8 and 13 can preferably be constructed such that they independent of the pressure drop over the valves 8 and 13 deliver a volume flow which is more or less proportio¬ nal to the input signals. By the fact that both objects and pressure fluid source are governed exclusively upon information from position transmitters it is their quali¬ ty that substantially decides the guide results. The re¬ maining components can have relatively great defects with¬ out effecting the total result. The apparatus in its en- tirety can accordingly operate well both in new unworn condition and in weared condition. The pressure fluid source 5 is preferably constructed as a variable reset pump but can also be a fixed non-reset pump provided with a shunt valve which via the set device 6 shunts undesired volume flow from the supply conduit 9 to the return conduit 10. The position transmitters 7 and 12 can be constructed in many ways, for instance be potentiometers or other all- electric devices. As position transmitters can also be used volume meters which measures the volume delivered out of or supplied into one side of the object and there¬ by calculate the position, the speed and the acceleration of the object. Measurement with volume meters is particu¬ larly useful in dangerous environments where electric transmitters can be unsuitable. Volume meters or trans¬ mitters can also, if they can be made with low cost and with good accuracy, be an alternative to all-electric position transmitters. Fig. 2 illustrates such an alternative having a volume meter 14 as position transmitter instead of a position transmitter 7 according to Fig. 1. The object 3 is const¬ ructed as a piston/cylinder-device and the volume meter 14 is arranged between the cylinder and a directional valve 15 provided with transmitter 16. Fig. 3 illustrates an embodiment in which a volume meter 17 is positioned in the supply conduit 9 after the pres¬ sure fluid source 5, and the volume meter 17 is connected to the guide system 2. Hereby, a fast indication can be obtained if any leakage should arise, for instance hose brake in the supply conduit 9. The volume flow delivered from the pressure fluid source 5 is measured and is re¬ turned to the guide system 2 and is compared with the sum of all volume flows delivered from the supply conduit to the tank 11, and as measure value for each object 3, 4 is valid the volume flow calculatable from the position measurement by means of the position transmitters 7, 12, 14, or if another value exists, for instance 10% lower, the volume flow belonging to a flow from supply conduit to object proportional to the guide signal of the valve 8, 13, 15. The technique required for realizing the electronic guide system 2 is today known and commonly used for instance in numerically controlled machine tools and robots and in electronic guide systems in many other civil and military applications. An apparatus according to the invention can of course be completed with further functions, such as • memories etc, making possible for a machine guided by the apparatus to excercise and repeat as well as record move¬ ments automatically as well as for instance allow permitted and unper itted operation field and mode of movements. Be- sides the fact that each object can be given a setable and resetable permitted and unpermitted movement field, the permitted field can position y position be given a maximum speed making the speed softly decreasing towards the end positions and so that accelerations and dynamic forces are maximized.

Claims: CLAIMS : 1. A method for electrohydraulic governing of at least movements of objects (3,4) actuated by pressure fluid and connected to a device, one at the time or several simul¬ taneously, by means of a valve means (8,13,15) each, which by means of conduits are connected in parallel to a pressure conduit (9) from a pressure fluid source (5) and a return conduit (10) to tank (11) , wherein the pres¬ sure fluid source and the valve means receive input signals from an electronic guide system (2) actuatable by an outer impulse generating guide means (1) and are controlled in ' such a manner, that on one hand the volume flow in the pressure conduit to said valve means is maintained suffi¬ ciently large so that each operated object shall receive the volume flow required in order that the object speed, which the input signal to respective valve means pursues, shall not be underpassed with more than a limited quantity, for instance 10%, and on the other hand the pressure in the pressure conduit upon governing energy absorbing objects never exceeds the highest pressure requirement of the, on each occasion, operated objects with more than what is re¬ quired for overcoming flow from the pressure fluid source through the pressure conduit and through a relatively open valve means to the object requiring highest pressure, c h a r a c t e r i z e d i n that the governing of the objects (3,4) at each time occurs by a combination of that - the input signal to the pressure fluid source (5) and each valve means (8,13,15) is either the input signal de¬ sired from said outer guide means (1) or at most the limited input signal from the electronic guide system (2) which is possible to achieve considering the limitations of the pressure fluid source in effect and volume flow, - the volume flow flowing via said valve means (8,13,15) from the pressure fluid source (5) to the objects (3,4) is governed so that the sum of the input signals of all said valve means strives to govern out a total volume flow which always is a small quantity larger than what the pres¬ sure fluid source via its input " signal is governed out to deliver to the pressure conduit (9) , and consequently in each case the object requiring the highest pressure is supplied a lower volume flow than what the input signal to the valve means of this object tries to govern out, and - the position of each object (3,4) , whether the movement is rotating or linear, is measured and the measurement values are returned to the electronic guide system. 2. A method according to claim 1, c h a r a c t e r i z e d i n that the volume flow from the pressure conduit (9) to each object (3,4) is governed by an input signal to said valve means (8,13,15) of the object which in each moment is not higher than that said valve means maximum strives to govern out a speed which is for instance 120% of the speed existing in the moment. 3. A method according to claim 1 or 2, c h a r a c t e ¬ r i z e d i that said valve means (8,13,15) of the object (3,4) always strives to govern out a higher speed for the volume flow from the object to the return conduit (10) than for the volume flow from the pressure conduit (9) to the object. 4. A method according to any of the claims 1-3, c h a r a c¬ t e r i z e d i n that in case of energy absorbing objects (3,4) the speed is determined by the flow from the pressure conduit (9) to the objects, wherein said valve means (8,13, 15) via the flow from the objects to the return conduit (10) strives to govern out a higher object speed, for instance 30% higher. 5. A method according to any of the claims 1-3, c h a r a c¬ t e r i z e d i n that in case of energy delivering objects (3,4) the speed is determined by the flow from the objects to the return conduit (10),wherein said valve means (8,13, . 15) via the flow from the pressure conduit (9) to the ob¬ jects completely block the flow or maximum strive to govern out a lower object speed, for instance 30% lower. 6. A method according to any of the preceding claims, c h a r a c t e r i z e d i n that the movements and the speeds desired by the impulse delivering guide means (1) are achieved in proportion to the portion of the limited access of volume flow from the pressure fluid source (5) to the objects (3,4). 7. A method according to any of the claims 1-6,c h a r a c - e r i z e d i n that the delivered volume flow from the pressure fluid source (5) is measured and the measured va¬ lue is returned to the electronic guide system (2) for -comparison with the sum of all volume flows flowing from the pressure conduit (9) to the objects (3,4) . 8. A method according to any of the preceding claims, c h a r a c t e r i z e d i n that said device to which the objects (3,4) are connected for governing said device, has limitations in position, speed and acceleration in optional combination corresponding to the limitations in the movement of each object. 9. A method according to any of the preceding claims, c h a r a c t e r i z e d i n that each object (3,4) within all its movement field is position by position given such a maximum allowed speed that constant maximum allowed acceleration is not exceeded. 10. An apparatus for electrohydraulic governing of at least movements of objects (3,4) being actuated by pres¬ sure fluid, one at at the time or several simultaneously, and connected to a device, including a pressure fluid source (5) , a pressure conduit (9) from the pressure fluid source to the objects (3,4) , a return conduit .(10) from the objects (3,4) to tank (11), a valve means (8,13,15) at each object (3,4), said valve means being positioned between the objects and the pressure conduit (9) and the return conduit (10) , respectively, and connected in parallel to these conduits, a position transmitter (7,12,14) at each object (3,4), -an electronic guide unit (2) , to which an impuls delivering means (1) is connected for delivering input signals to said guide unit and to which the pressure fluid source (5) and the valve means (8,13,15) are connected for input signals to said source and said valve means from said guide unit, said position transmitters (7,12,14) being connected to said guide unit for input signals through said guide unit, and a control means (6) at the pressure fluid source (5) arran¬ ged on one hand for maintaining the volume flow in the pres¬ sure conduit (9) to said valve means (8,13,15) sufficiently large so that each operated object (3,4) receives the volume flow required so that the object speed, which the input sig¬ nal to respective valve means persues, is not underpassed with more than a limited quantity, for instance 10%, and on the other hand the pressure in the pressure conduit (9) upon governing energy absorbing objects never exceeds the highest pressure requirements of the, on each occasion, ope¬ rated objects with more than what is required for overco¬ ming the flow from the pressure fluid source through the pressure conduit and through a relatively open valve means to the object requiring highest pressure, c h a r a c t e r i z e d i n that said guide unit (2) is arranged to deliver input signals to said control means (6) of the pressure fluid source (5) and to each valve means (8,13,15) either the desired input signal or at most the limited input signal possible to achieve considering the limitations in effect and volume flow of the pressure fluid source, said control means (6) of the pressure fluid source (5) governs the volume flow through the pressure conduit (9) and said valve means (8,13,15) so that the sum of all the input signals from said valve means strives to govern out a total volume flow which always is a small quantity larger than what the pressure fluid source via its input signal is governed out to deliver to the pressure conduit, and thereby in each case the object (3,4) requiring the highest pressure is supplied with a lower volume flow than what the input signal to the valve means of this object tries to govern out, and the position transmitters (7,12,14) are arranged to mea¬ sure the position of each object (3,4) and return the measured values to said guide unit (2) .

Inventors: STENLUND STIG, STENLUND, STIG
Applicants: FLUTRON AB
Application year: 1988
Main classification: F15B21
IPC codes: F15B11, F15B21