fig1 shows a fundamental hydraulic chart for a striking unit s in a preferred embodiment of the invention , where crossing conduits without points do not communicate . the figure shows a striking unit s comprising a cylindrical housing 1 , containing a through work piston 2 . preferably , the piston 2 is journalled in its two ends with a first bearing 20 and a second bearing 21 . there is also a third bearing 22 in the middle of the piston implying that two chambers are formed , a drive chamber 11 and a second chamber 10 . the piston 2 is intended to transfer high kinetic energy to a blank / tool for high speed processing . the drive chamber 11 is connected to a valve means 5 , a pressure - controlled on / off - valve , preferably a cartridge valve , via a first conduit l 1 . the cartridge valve 5 is via a conduit l 3 connected to a pilot pressure pp , via a valve , preferably via a pilot valve 7 . the expression pilot valve means some kind of valves fulfilling the functionality of controlling the on - off / cartridge valve 5 , which preferably comprises a multipath valve , which by means of a comparatively small hydraulic flow may quickly adjust an on / off valve for a larger flow . further , the cartridge valve 5 is connected to a system pressure ps via a conduit l 2 . the cartridge valve 5 is also connected to a pressure accumulator 5 ′ in order to achieve a rapid pressure increase in the drive chamber 11 at acceleration . also the pilot valve 7 is connected to a pressure accumulator 7 ′, which contributes to a quicker emptying of the drive chamber 11 . the second chamber 10 is connected to a system pressure ps via a conduit l 2 . the chart also includes a control system 9 , a sensor 6 , a servo valve 90 and a non - return valve 91 . the non - return valve 91 is connected to a cistern accumulator 91 ′ to contribute to a quicker emptying at a pressure reduction . the three bearings 20 , 21 , 22 mentioned above have preferably mutually different diameters , which implies that the effective areas of the piston 2 in the drive chamber 11 and the second chamber 10 , respectively , differ . the effective area a kolvö of the piston 2 in the drive chamber , which the oil influences , is larger than the effective area a kolvu in the second chamber 10 . in the second chamber 10 there is preferably always a system pressure ps . the pressure pa of the drive chamber 11 may be considerably lower than the system pressure ps to keep the piston 2 in balance . the following relation is valid to keep the piston 2 in balance , where m kolv is the mass of the piston 2 and g is the acceleration due to gravity : in order to be able to operate the cartridge valve 5 safely and rapidly , a pilot pressure pp is preferably used , which is larger than the system pressure ps . the work cycle of the striking unit s may be divided into four parts : positioning , acceleration , hit and return motion to symbolize the pressures which exist in different conduits in fig2 and 5 in the different cases , the pressures are symbolized according to the following : pp =----, ps =• • • • •, p regler = xxxxx , and p tank =++++++, wherein preferably pp & gt ; ps & gt ; p regler & gt ; p tank in fig2 the step positioning is shown , where the control system 9 keeps the piston 2 at a pre - chosen distance from the blank / tool 4 by means of a servo valve 90 . the current position of the piston 2 is measured by the sensor 6 , and by means of an adjustment function the control system 9 adjusts the piston 2 to the chosen position by means of the servo valve 90 by adjusting the pressure p regler in the conduit l 1 . if the piston 2 is too far from the blank / tool 4 , the pressure p regler will be increased and hence the piston 2 is moved closer to the tool . if the piston 2 is too close to the blank / the tool 4 , the pressure p regler will be reduced and hence the distance to the tool is increased . when the piston 2 is at the pre - chosen distance , it is kept in balance according to the balance condition above . the pressure px is the pressure existing in the conduit l 4 and acting on the operation area ax of the cartridge valve cone . the pilot valve 7 is put in a maximally negative open state ( p → b ), so that px = pp , and hence the cartridge valve 5 is kept closed . this guarantees that it does not enter into the system pressure ps to the drive chamber 11 . the non - return valve 91 is closed and put into a center position during the positioning . in fig3 the step acceleration is shown , where the adjustment function is inactivated , wherein the servo valve 90 is put into a center position at the same time as the pilot valve 7 opens ( somewhat ) positively ( b → t ), so that the operation area ax of the cartridge valve cone is connected to a cistern 8 . then , the pressure px will fall and the cartridge valve 5 opens , as the pressure at the other side of the cone is larger , which implies that a instantaneous connection to the system pressure ps in the drive chamber 11 is obtained . with the system pressure ps also in the drive chamber 11 a resultant downwardly directed force is obtained , when : which implies that the piston 2 quickly accelerates downwardly , often with a resultant speed of well above 10 m / s , rather often above 12 m / s . the cartridge valve 5 thus connects the system pressure ps with the first conduit l 1 , so that the drive chamber 11 is pressurized , and connects then also the flow path between the chambers , via l 1 and l 2 , so that oil which has been displaced from the lower chamber 10 may flow to the drive chamber 11 . thanks to the fact that the cartridge valve 5 is connected to the pressure accumulator 5 ′ a quick pressure increase in the drive chamber 11 is reached . the non - return valve 91 is closed and put in the center position during acceleration . fig4 shows the step hit . the piston 2 hits the blank / tool 4 to be processed and gets through its own elasticity and the elasticity of the blank / tool a certain return motion / bound . as the piston 2 has an approximately constant acceleration until it hits the blank / tool 4 , the hit speed depends on the distance to the blank / tool 4 at the positioning before the acceleration phase . fig5 shows the step return motion . after the hit , the pressure pa in the drive chamber 11 has to be quickly reduced , so that the piston 2 is not again forced downwards and risks to make a second hit . the pilot valve 7 is put to a negatively open position , so that the operation area ax of the cartridge valve cone obtains the pressure pp and moves towards a closed position . the non - return valve 91 is put to a positively maximal position so that the drive chamber 11 is connected to the cistern 8 , wherein the system pressure ps in the second chamber 10 drives the piston 2 away from the blank / tool 4 . ( may in this case instead be opened to a negatively maximal position , which gives the same function , as the openings p and t are connected and the openings a and b are connected ). the adjustment function is activated , which implies that the servo valve opens negatively ( a → t ) to reduce the pressure in the drive chamber 11 and to control the piston 2 to the determined start position according to the step positioning . the start position needs not be the same from stroke to stroke but may vary . by means of the sensor 6 , which stands in communication with the control system 9 , the position of the piston 2 may be sensed , and after a certain time period or at a predetermined position of the piston a signal is given to the control system 9 , which influences the different valves as described above . as well the pilot valve 7 as the non - return valve 91 are thus connected to the accumulators 7 ′, 91 ′, which contribute to a quicker emptying of the drive chamber 11 . it is very advantageous as quickly as possible to empty the drive chamber 11 to be able to adjust the piston 2 to the start position for the next stroke . thanks to the design described above , a solution with short paths and a high flow , an optimal dimensioning of the cistern conduit system and cistern accumulators is obtained , which results in a quick and effective pressure reduction and a return of the piston 2 , i . e . the piston 2 may be “ caught ” without obtaining double strokes / double bounds . a cistern accumulator of the “ high flow ” type ( usually equipped with a disk valve ) is preferred , in order to be able to handle large / quick flows , preferably min . 900 l / min , more preferred min . 1 , 000 l / m . suitably the accumulator ( or more ) is adapted so that the risk is avoided that it reaches / they reach the bottom , i . e . the dimensioning should be such that a certain auxiliary volume remains also at a maximal demand . the adjustment of the piston position before a stroke is performed by means of a servo function in accordance with the description above . the control system 9 gives a dynamic control of the servo valve 90 and the pilot valve 7 , which influences the cartridge valve 5 for a stroke by dynamically calculating the time control based on the model of the striking unit , distance - time function , the stroke length chosen , etc . output from the calculation gives a time for how long time it takes for the piston 2 to reach an impact cap 41 , and thereafter it is used as input to close the valves . the choice of parameters for the adjustment algorithm is adapted to the respective striking unit s . preferably , it may be adaptive after the calculation of the start parameters . it is the question of extremely quick progresses , which provides a control accuracy of tenths of a millisecond . thus , the function of the pressure accumulators is first of all to guarantee that there is oil enough during quick progresses . without the pressure accumulators a much larger pump would have been required to be able to meet the large flows occurring during a short time . the cistern accumulators relieve the system by making it possible for them temporarily to be filled with oil , when the drive chamber is to be emptied . it would also take much longer time before the pressure is reduced , as the oil then must be emptied to the cistern 8 through cistern conduits with the drawback that , except the long path , there is a certain resistance in the hoses . fig9 shows a chart indicating when the different work cycles take places at a striking progress . on the x - axis of the chart the time is shown in ms and on the y - axis of the chart the position of the striking body is shown in mm . the continuous line shows a stroke performed according to the invention , while the broken line shows how a conventional stroke takes place . it may be seen that the two curves accompany each other during a first lapse of time , i . e . exactly the same acceleration and motion is achieved from the start position t 0 to the accomplishment of a stroke as well during part of the return motion . according to a conventional method , a number of re - strokes hereafter occur , which may result in undesirable consequences . according to the invention , this is avoided as the flow is rapidly changed in the drive chamber 11 and a quick emptying may be performed . at t 0 the acceleration thus starts , at t 1 the hit occur , at t 2 the piston 2 is caught and the return motion takes place , and at t 3 a new positioning of the piston 2 occurs , according to the description above . fig1 shows a chart of a real stroke , when the piston 2 has a mass of 250 kg and the mass of the anvil and the tool is 12 tons . on the x - axis of the chart the time is shown in ms and on the y - axis of the chart the position of the piston is shown in mm . the start position is marked t 0 , i . e . here the acceleration starts , at t 1 a hit occurs , at t 2 the piston 2 is caught , and at t 3 a new positioning of the piston 2 , takes place , i . e . a time of 35 ms from start ( t 0 ) to the capture ( t 2 ) of the piston 2 . depending on the machine size and the striking parameters the time between the start of the acceleration ( t 0 ) and the new control of the piston 2 by the control system ( t 2 ) may be in the range of 2 to 500 ms . more preferred the time range below is dependent of the mass of the piston 2 : the mass of the piston is up to 25 kg . the preferred time range is 2 to 50 ms , more preferred below 30 ms . the mass of the piston is 25 to 250 kg . the preferred time range is 4 to 150 ms , more preferred below 80 ms . the mass of the piston exceeds 250 kg . the preferred time range is 8 to 300 ms , more preferred below 150 ms . the mass of the anvil and the tool is advantageously larger than the mass of the piston 2 so that the piston 2 will bounce at a hit . it is also possible to practise the invention if the mass of the anvil and the tool is equal to or somewhat smaller than the mass of the piston 2 , but the foregoing is usually preferred . fig6 shows a cross - sectional view of a tool solution 4 to avoid double - bounds according to the invention , seen from the side . the figure shows a tool set comprising a lower tool element 42 , an upper tool element 40 , and impact cap 41 arranged on top of the upper tool element , wherein the tool elements 40 , 42 are movable in relation to each other . the tool elements 40 , 42 often comprise a patterned surface towards the blank to be processed but they may also be smooth . the material 400 to be processed is arranged between the lower tool element 42 and the upper tool element 40 . the tool set is arranged in a tool housing , not shown , which is arranged on a stationary or movable anvil . depending on how the finished product / plate 400 is to look like , at least one of the tool elements 40 , 42 often comprises an engraving 40 a , 42 a , which is congruent with the surface of the finished product / patterned plate 400 . the lower tool element 42 is preferably stationary and consists of a pad , while the upper tool element 40 is a punch striking towards the pad with the blank 400 to be formed arranged therebetween . in the case shown in fig6 the impact cap 41 is pressed towards the upper tool 40 , which in its turn presses against the blank 400 with a well - defined holding force f ( preferably from some tons and upwards depending on the pressure force / energy necessary for the forming work ). this force f is so large that the tool is not permitted to bounce upwards after a stroke . the forming of the plate 400 takes place by the tool elements 40 , 42 striking towards each other as the piston 2 with very high kinetic energy is struck against said impact cap 41 . the tool 40 and the impact cap 41 are suitably pressed by a spring force against the blank 400 . it is also possible that the impact cap 41 and the upper tool element 40 are an integrated unit , which would imply that the need to keep them connected then would be deleted . it is advantageous also at the forming of patterned plates 400 if a forming tool 4 does not come into contact with the blank two times or more as there then is a risk that the tolerances of the plate 400 is not met . fig7 shows an alternative embodiment to prevent rebounds against the blank 400 to be formed . the figure shows parts of the tool housing 43 , containing a tool elevator comprising a lower tool element 42 , an upper tool element 40 as well as a impact cap 41 arranged on top of the upper tool element , wherein the tool elements are moveable in relation to each other . the tool elevator is pressed with a well - defined holding force against the periphery of the blank 400 , and the material / plate 400 to be formed is arranged between the tool elements 40 , 42 . the upper tool element 40 comprises in its upper part a border 47 extending upwards on each side . the tool housing 43 is constructed with a corresponding cavity 46 so that the border 47 will get space to move downwards at a stroke by the striking piston 2 against the impact cap 41 . at the forming of the plate 400 , the piston 2 is struck with very high kinetic energy against said impact cap 41 . the upper tool element 40 bounces upwards after a stroke , and air , alternatively some other gas , is blown into the space formed between the upper tool elements 40 and the plate 400 ( see arrows 44 a , 45 a ) via channels 44 , 45 in the tool housing 43 . the air blown into the space 48 forms an air bag which prevents the upper tool element 40 from reaching the plate 400 when it falls down again . fig8 shows still an alternative embodiment of a forming tool 4 , which is advantageous to use at the production of stamped plates , when the material is so thin that , if the tool solution 4 described in fig6 would be used , the material has already been completely processed by the exerted force f . in the example shown , a damping / resilient element is preferably arranged in the cavity 46 , between the tool housing 43 and the border 47 of the upper tool element . the element 49 exerts a spring force upwards against the border 47 of the upper tool element , a spring force which is small enough so that the forming will not be hindered ( however , it gives resistance so that somewhat more forming energy is required than if it had not been there ). at the forming of the blank 400 the piston 2 is struck with very high kinetic energy against said impact cap 41 . after the forming , when the piston 2 , the impact cap 41 and the upper tool element 40 have left the blank 400 , the spring force is large enough to prevent the upper tool element 40 from reaching the blank 400 again . it is realized that the different embodiments of the tool solutions described with reference to fig6 to 8 as such may be the subject for divisional applications . the invention is not limited to the description above but may be varied within the scope of the following claims . for instance , it is realized that the number of valves and accumulators as well as their size in the examples described may vary , the number and the size is dependent on the size of the machine . in the description , a cartridge valve is described as an example , but it is realized that also other quick valves may be used . the man skilled in the art realizes that the invention idea also comprises another material processing than the one described above , e . g . punching , cross - cutting , stamping , and compacting of powders , and that the striking unit may be inverted so that the piston strikes upwards instead of downwards , as described . it is also possible that a striking unit and an anvil is placed on resilient feet , so that the anvil may move . in this way , the anvil may get a counter - directed motion towards the acceleration of the piston . although a cartridge valve without any spring is shown in the figures , the man skilled in the art realizes that the invention idea comprises cartridge valves both with and without springs .