WO2011023172A1

WO2011023172A1 - Cutting method for reducing cutting impact

Info

Publication number: WO2011023172A1
Application number: PCT/DE2010/000994
Authority: WO
Inventors: Olaf Marthiens
Original assignee: Gottfried Wilhelm Leibniz Universität Hannover
Priority date: 2009-08-25
Filing date: 2010-08-25
Publication date: 2011-03-03

Abstract

The invention relates to a cutting method for reducing the cutting impact of a cutting machine (10) that has a cutting tool (30), comprising the following steps: moving a lower tool (26) and an upper tool (28) of the cutting tool (30), between which a metal plate is arranged, toward each other by means of a drive (14) comprising a crank, detecting a beginning of a cutting impact (t_beginning), supplying current to at least one linear motor (38) after the beginning of the cutting impact (t_beginning) so that a restoring force (F_restoring(t)) is applied to the cutting tool (30), which restoring force acts against an oscillation (Δx(t)) of the cutting tool (30) triggered by the cutting impact (as in DE 10 2008 011 024), wherein the linear motor (38) is supplied with current from a specified start time (t_start) until a specified end time (t_end) after the beginning of the cutting impact (t_beginning) according to a current supply pattern (80) that corresponds to a standard current supply pattern, calculating an evaluation value (B) after the end time from the oscillation (Δx(t)) of the cutting tool (30), which evaluation value is a measure of an intensity of the oscillation (Δx(t)) after the beginning of the cutting impact (t_beginning), changing the current supply pattern (80) so that a second current supply pattern is obtained, performing a second cut, calculating a second evaluation value of the oscillation (Δx(t)) of the cutting tool (30) after the beginning of the cutting impact (t_beginning) for the second cut, and if the second evaluation value is less than the first evaluation value, setting the second current supply pattern as the standard current supply pattern.

Description

Cutting method for reducing a cutting stroke

The invention relates to a cutting method for reducing a cutting stroke of a cutting machine having a cutting tool. With regard to a second aspect, the invention relates to a cutting machine with a crank drive.

Cutting methods, such as shear cutting or sheet punching, are typically performed with a cutting machine having a two-part cutting tool, namely an upper tool and a lower tool. The upper tool is moved by a drive with a lifting movement and leads to a movement on the lower tool from. At the beginning of the cutting process, it sits on the workpiece to be cut, for example the sheet metal, which rests on the lower tool. The force exerted by the upper tool on the workpiece increases, that is, the cutting machine springs up, until the material of the workpiece abruptly fails along a cutting line and the cut is performed.

At the moment of failure, the force between upper tool and lower tool suddenly drops. This phenomenon is called a cutting blow. The cutting stroke results in an oscillation of the upper tool relative to the lower tool, in which the upper tool rubs on the workpiece and thereby wears. Due to this wear, the component quality of the cut slugs sings. For example, the cut is less smooth, so that the edge of the Butzens must be reworked, which is expensive. To avoid this, the cutting tool must be replaced regularly, which is complicated and expensive. There are therefore dampers between the upper tool and the upper tool moving drive provided to dampen the triggered by the cutting shock oscillation of the cutting tool as quickly as possible. From WO 98/55779 an electromagnetic damper is known in which coils are arranged between rows of permanent magnets. Upon movement of the coils attached to the parts to be damped relative to a fixed part, an electrical voltage is induced in the coils, which voltage is amplified by an electrical amplifier. With the amplified voltage second coils are energized, which are arranged between the permanent magnets. This leads to increased damping. A disadvantage of this system is that it is not suitable for the large forces occurring during the cutting stroke. From DE 95 29 134 a friction damper is known. However, this has the disadvantage that occurring after the cutting shock oscillations of the cutting tool can be damped only poorly.

From EP 0 937 572 A2 a press and a punching machine are known, which are driven by linear motors. A disadvantage of such presses, the very strong linear motors must be used to apply the considerable forces. From WO 98/55779 A1 a damper in the form of a linear motor is known. In DE 10 2008 011 024, to which this application is an additional application, the use of a linear motor for reducing the cutting stroke is described. The present application specifies a development that simplifies the application of the linear motor and leads to a particularly effective damping, even if, for example, change the material properties of the sheet. The invention solves the problem of achieving a particularly effective damping for the invention according to the main patent application, by a cutting method according to claim 1.

According to a second aspect, the invention solves the problem by a cutting impact damping device according to claim 8.

An advantage of the main invention is that already then the oscillation of the cutting tool counteracting restoring force can be applied to the cutting tool, for example, when the upper tool and the lower tool relative to each other substantially not yet move. Immediately before the cutting stroke, the cutting machine is spring-loaded. Immediately after the beginning of the cutting stroke, for example, the upper tool is greatly accelerated toward the lower tool. At the beginning of this acceleration, the relative speed between upper and lower tool is still very low. The acceleration, however, considerable. By measuring the acceleration and by immediately thereafter energizing the linear motor, the restoring force can be applied very quickly.

In conventional dampers, the damping force depends on a relative speed between the upper and lower tools or on a reivativ position of the upper and lower tool relative to each other. From the motion characteristic of the upper tool relative to the lower tool, it follows that initially the acceleration assumes a large value and only then does the relative speed. The method according to the invention can therefore significantly better damp the oscillation of the cutting tool triggered by the cutting impact, in particular the oscillation of an upper tool into a lower tool, than methods according to the prior art. It is also advantageous that the damping of the oscillation triggered by the cutting impact is achieved without rubbing against one another and thus rapidly wearing parts. It is another advantage that the damping of cutting stroke can be quickly adapted to changing boundary conditions. If, for example, the mass of the upper tool or the material of sheet metal to be cut changes, it is sufficient to adapt the time profile of the energization of the linear motor in order to again obtain the optimum damping.

It is advantageous for the development according to the additional application that changes in the material properties of the sheet can be quickly corrected. It is another advantage that no human intervention is necessary for this.

In the context of the present description, a cutting tool is understood in particular as a two-part or multi-part cutting tool which comprises an upper tool and a lower tool. Under the Bestromungsmuster is understood in particular a sequence of electrical currents or voltages, with which the linear motor is acted upon. The Bestromungsmuster is stored for example in a digital memory of the electrical control. The individual currents or voltages usually follow one another directly and thus without any idle time.

In principle, any desired time after the beginning of the cutting stroke can be selected as the end time. It is favorable, however, to choose such a time at which the oscillation of the cutting tool has subsided substantially. Under the evaluation value, which can also be referred to as a fitness value, any value is understood, which increases as the oscillation increases. In particular, such an evaluation value is used, which is characterized in that it is small when the wear of the cutting tool is low and is large when the wear is large. In other words, an evaluation value that positively correlates with the wear is used. The evaluation value can be determined, for example, by the root mean square value from the oscillation profile of the oscillation. The step of changing the flow pattern is understood in particular to mean that at least one of the current or voltage values is changed. This can be done, for example, by multiplying at least one of the values in the energization pattern by a random number or by adding a value to at least one of the values. In this case, the current pattern is changed increasingly smaller with increasing number of changes in the rule. The degree of change is proportional to the valuation value and inversely proportional to the number of changes, so that after a large number of changes, the optimization of the valuation pattern is almost complete. The decisive change in the current flow pattern occurs at the beginning of the optimization. A fast-changing rating value delays the end of the optimization, but can also restart the near-completion optimization. If the evaluation value is ideally zero, then there is no oscillation and a change in the current pattern does not take place. The optimization of the Bestromungsmusters is almost completed until a change in the evaluation value is due to a new change in the course of the oscillation again. If, for example, the usual scalar product, which is calculated by the root from the sum of the squares of the values for the currents or voltages of the current pattern, is used, the current pattern is only changed in such a way that the scalar product of two consecutive energizing patterns differs by less than 10%.

In the method described according to claim 1, therefore, the excitation pattern is optimized in the context of a genetic or evolutionary optimization algorithm such that the evaluation value decreases and at best becomes minimal. In this way, the oscillation of the cutting tool is minimized without having to know in advance which physical relationships influence the oscillation.

If, as preferred provided, only the oscillation of the cutting tool arrives after the start of the cutting stroke in the evaluation value, it may happen that the cutting tool is caused to oscillate by the linear motor before the cutting force begins. Such oscillation has the advantage that an oscillation of the cutting tool is suppressed particularly effectively after the start of cutting.

In the static mean, a temporally monotonically decreasing evaluation value is obtained and the cutting impact is particularly effectively damped.

The evaluation value may, for example, be the root of the sum of squares of the oscillation values, the sum of the squares of the oscillation values, the sum of the absolute values or a sum of higher integer exponents of the oscillation values. However, the root of the sum of squares of the oscillation values has proved particularly suitable.

It is favorable if, between the start time and the end time, the oscillation is recorded at more times than the energization pattern has entries. If, for example, the energization pattern comprises one-hundredth consecutive currents or voltages, then the oscillation should be recorded at least at one hundred points in time. Usually will the number of measuring points of the measured oscillation be significantly greater than the number of currents or voltages in the current flow pattern.

According to a preferred embodiment, the starting time is before the respective cutting stroke beginning. This means that the linear motor can already be energized before the cutting tool comes into engagement with the metal sheet. In this way, the oscillation of the cutting tool can be attenuated particularly effective after cutting start. The energization pattern preferably corresponds to a quantity of temporally equidistant current or voltage values. The linear motor is acted upon at the respective time with the corresponding current or the corresponding voltage. Particularly suitable are current patterns with at least 50 current or voltage values have been found. Also favorable are energization patterns with at most one hundred current or voltage values. In this case, after about three hundred cuts, a reduction of the maximum amplitude of the oscillation to a fraction, for example half, of the original value without cutting impact damping will be achieved. It is particularly advantageous if the end time corresponds to the time at which the upper tool comes out of engagement with the sheet. After this time oscillations of the cutting tool for wear no longer matter. It is particularly favorable if a lead time period between the start time and the start of cutting is at least one quarter of a damping period between the beginning of cutting and the end time. It has been shown that such a particularly efficient damping is possible. As a result, the oscillation with the optimized current application pattern is intensified by the cutting impact in such a way that, ideally, with the inferferential cutting impact oscillation after the cutting stroke, no resulting oscillation occurs any more. occurs. After the cutting stroke, the remaining oscillation, while the cutting punch is engaged with the sheet, is damped by the subsequent flow pattern. For the optimization, there is only one continuous energization pattern consisting of the pattern before and after the cutting stroke. In a "natural" way, the optimization results in an energization pattern that enhances the oscillation before the cutting stroke and damps it after the cutting stroke.

In a preferred embodiment, the method according to the invention comprises the steps of detecting a cutting tool position along a stroke path of the cutting tool, energizing the at least one linear motor so that the cutting tool applies a biasing force against a workpiece to be cut, before the cutting stroke beginning and releasing the biasing force immediately after the start of cutting. This ensures that the force necessary for cutting the workpiece is applied to a certain extent by the linear motor. The cutting machine springs less, and the cutting stroke can be damped even faster. For particularly rapid damping of the cutting stroke, the method according to the invention particularly preferably comprises the step of applying the cutting force to the cutting tool after releasing the biasing force.

The beginning of the cutting stroke can be detected particularly precisely if the detection of the beginning of the cutting stroke involves detecting an acceleration of the cutting tool, in particular of an upper tool. As stated above, the acceleration is large immediately after the beginning of the cutting stroke, but the relative speed between the upper tool and the lower tool is low. A high acceleration is therefore a clear and easily measurable indication of the beginning of cutting stroke. In other words, the linear motor is energized so that it always applies a restoring force on the cutting tool or a part of the cutting tool, such as the upper tool or the lower tool, which is temporally variable and a phase shift relative to the time-varying vibration of the cutting tool, or of the upper tool relative to the lower tool has. The phase shift is substantially at 180 °. This means that it is possible, but not necessary, for the phase shift to lie within the control accuracy at 180 °. For example, it is sufficient if the phase shift is between 170 ° and 190 °.

In asymmetric workpieces, the cutting impact may occur at different points along a cutting line at different times. This results in a slight tilting of the cutting tool or of the upper tool relative to the lower tool. This results in an oscillation of the cutting tool or an upper and / or lower tool about a pivot axis, which also leads to wear. This oscillation is avoided if the detection of the cutting start of impact and the energizing of the at least one linear motor is carried out at two, in particular at four points, wherein the at least two points are arranged in particular at corners of the cutting tool. In this case, the restoring force also sets earlier, at a point where the cutting stroke used to be earlier, so that the oscillations around the pivot axis are significantly reduced. Preferably, the method comprises the steps of detecting an angular position of the cutting tool and energizing the at least one linear motor so that the angular position of the cutting tool approaches a desired angular position. Thus, it can be provided that the desired angular position causes a part of the cutting tool to touch the workpiece earlier than other parts of the cutting tool. For example, the desired angular position is selected so that the cutting stroke along the cutting line substantially to same time occurs. The angular position is understood in particular to mean the orientation of the cutting tool relative to a plane in which the workpiece and / or the lower tool is arranged. A cutting impact damping device according to the invention preferably has a double-comb linear motor. A double-comb linear motor is understood in particular to mean a linear motor in which two oppositely arranged partial primary parts surround a secondary part having permanent magnets. Double comb linear motors are short in construction and therefore well suited for short-stroke cutting machines.

Particularly preferably, both primary parts share all permanent magnets. In other words, for example, each north pole of a permanent magnet interacts with one of the partial primary parts, whereas the south pole of the same permanent magnet interacts with the other primary partial part. In other words, there is only one layer of permanent magnets for both partial primary parts of the primary part. An advantage of this is the particularly compact design. It is particularly preferred that the secondary part has a matrix of fiber-reinforced plastic, in which the permanent magnets are embedded. Fiber-reinforced plastic has a high strength and keeps the permanent magnets safely in place. At the same time the plastic is electrically non-conductive, so that no eddy currents are induced, which could affect the dynamics of the linear motor.

A particularly durable and at the same time robust guidance is obtained when the secondary part has on both sides a guide rail, by means of which the secondary part is guided centrally between the two partial primary parts. For example, the secondary part is guided by a guide carriage on the two partial primary parts. Add exactly in the middle between the sub-primary parts the attractive forces of the primary parts to zero, so that the attractive forces that are exerted by the two sub-primary parts respectively on the secondary part, are completely absorbed via a compound of the two sub-primary parts. Since, consequently, no forces acting perpendicularly on the partial primary parts have to be absorbed at the secondary part, the guidance of the secondary part is particularly wear-resistant.

A particularly good magnetic closure and at the same time a magnetic shielding are obtained when the guiding machine is ferromagnetic.

In a preferred embodiment, laterally outside the guide rail, a distance measuring sensor, in particular a magnetic distance measuring sensor, is arranged for measuring a position of the secondary part relative to the primary part. Despite strong permanent magnets in its immediate vicinity, the magnetic displacement sensor delivers reliable measured values since the ferromagnetic guide rail effects a magnetic closure, so that only a weak stray magnetic field exists outside the guide rail.

A particularly dynamic linear motor is obtained when the secondary part has a plurality of teeth and has a toothed head winding with an open groove.

It is advantageous if a magnet pitch of the permanent magnets essentially corresponds to 6/7 of the pole pitch of the teeth of the secondary part. In this way, a particularly large force can be applied to the cutting tool. In the following, the invention will be explained in more detail with reference to an exemplary embodiment. It shows

FIG. 1 shows a schematic perspective view of a cutting machine according to the invention,

FIG. 2 shows a perspective view of a cutting impact damping device according to the invention, which is connected to a table and a plunger of a cutting machine according to the invention,

Figure 3 shows a schematic cross section through the inventive

Cutting impact damping device of Figure 2,

FIG. 4 shows a laminated core of a primary part of a linear motor of the sectional impact damping device according to FIG. 2, the laminated core being shown without coils,

5 shows the laminated core according to FIG. 4 with coils, FIG. 6 shows a perspective view of the cutting impact damping device according to FIG. 2,

FIG. 7 shows an exploded view of the cutting impact damping device according to FIG. 6,

FIG. 8 shows a schematic diagram of the cutting impact damping device according to the invention,

FIG. 9a a representation of a path of the ram once with and once without cutting stroke,

FIG. 9b shows an oscillation of the plunger relative to its ideal curve due to the cutting stroke; FIG. 10 shows a current application pattern, and

FIG. 11 shows a pattern of random voltages with the aid of which a further current application pattern is calculated from the standard energization pattern.

Figure 1 shows a cutting machine 10 according to the invention comprising a frame 12 and a drive 14 which moves a plunger 16 with a lifting movement up and down. The drive 14 may be any drive and in the present case comprises a crankshaft 18, a flywheel 20 and an electric motor 22 for driving the crankshaft 18. The frame 12 includes a table 24, in which a lower tool 26 is inserted. The lower tool 26 and the upper tool 28 are part of a cutting tool 30. As shown in the two part drawings left, the upper tool 28 has a punch 32 which has a smaller outer diameter by a small amount, as an inner diameter of a recess 25 in the lower tool 26, the also called a template. The cutting machine 10 is fed by a feed sheet, not shown, which then gets between upper tool 28 and lower tool 26 and cut out according to the shape of the punch 32. The result is the desired slug.

FIG. 2 shows the cutting tool 30 according to FIG. 1 and the plunger 16. Disposed between the plunger 16 and the table 24 is a cutting impact damping device 36 comprising a synchronous, double-planar linear motor 38 and a first fastening device 40 for fastening the linear motor 38 to the Plunger 16 and a second fastening device 42 for attaching the linear motor 38 to the table 24 includes. Driven by the drive 14 (see FIG. 1), the plunger 16 moves along a linear lifting path, which is indicated by the arrow P. If a metal sheet is positioned between upper and lower tool and the plunger 16 moves downwards, then the punch 32 (see FIG. 1) comes into contact with the metal sheet, which initially opposes mechanical resistance for further movement of the punch 32 downward. By the force of the drive 14, the plunger 16 is pressed further down, so that it comes to a spring-back. By the springing deforms, for example, the crankshaft 18 elastically.

If a critical force is exceeded, the sheet abruptly fails and the punch 32 penetrates into the recess 25 in the lower tool 26 (see FIG. An oscillation occurs between the upper tool 28 and lower tool 26 and thus an oscillation between the table 24 (see FIG. 2) and the plunger 16. This results in a relative movement between a primary part 44 and a secondary part 46 of the linear motor 38.

FIG. 2 additionally shows schematically pivot angles α, β, by which the plunger 16 can be inclined to a horizontal H. According to a desired angular position α = 0 and β = 0. Figure 3 shows a schematic cross section through the linear motor 38. It can be seen that the secondary part 46 has a plurality of permanent magnets 48.1, 48.2,. alternating polarities to each other. The primary part 44 comprises a first sub-primary part 50.1 and a second sub-primary part 50.2, which are constructed essentially mirror-symmetrically with respect to one another and lie opposite one another with respect to a longitudinal axis L of the secondary part 46. Because of their symmetrical structure, only the partial primary part 50.1 will be described in more detail below. The permanent magnets 48.1 ... 48.16 are arranged with a magnet pitch XM to each other, which indicates the distance between two upper edges of adjacent permanent magnets. The first part primary part 50.1 has a leafed laminated core 52.1, which has teeth 54.1 ... 54.6. The first tooth 54.1 is surrounded by a coil + U. The second tooth 54.2 is surrounded by a coil -U, the third tooth 54.3 is surrounded by a coil -V, the fourth tooth 54.4 is surrounded by a coil + V, the fifth tooth 54.5 is from a coil + W and the sixth tooth is surrounded by a coil -W. Each of the coils thus surrounds exactly one of the teeth 54.

FIG. 4 shows the laminated core 52.1 without coils. It can be seen that between each two teeth a groove 56.1 ... 56.5 is formed. The grooves 56 have on their sides facing the secondary part, that is, in Figure 4 on its upper side, a slot opening N, which is substantially as large as a Kehlungsbreite K at the bottom of the grooves. Although this reduces the power density of the linear motor, at the same time its inductance also decreases. It is obtained a particularly fast responding linear motor, which is advantageous for the present purpose.

The laminated core 52.1 has peripheral teeth 54.7, 54.8, which each form a groove 56-.6 or 56.7 with the first tooth 54.1 and the sixth tooth 54.6, which correspond in their geometrical dimensions to the remaining grooves 56.1... 56.5. All grooves 56 have the same cross sections.

FIG. 4 shows that a longitudinal bore 58.1... 58.4 is introduced into the laminated core 52.1 centrally between the next but two grooves centrally below the groove. Thus, a first longitudinal bore 58.1 is located between the first tooth 54.1 and the first marginal tooth 54.7. The second longitudinal bore 58.2 is located between the second tooth and the third tooth below the groove 56.2, the third longitudinal bore 58.3 is located below the groove 56.4 and the fourth longitudinal bore is disposed below the groove 56.7. In other words, the laminated core 52.1 of the linear motor comprises centrally below grooves between teeth of the primary part a longitudinal bore for suppressing parasitic magnetic field lines. This ensures that the magnetic field lines of a coil hardly scatter in adjacent teeth.

FIG. 5 shows the laminated core 52.1 with the associated coils. The coils are first wound independently of the sheet metal part 52.1 and fixed with impregnating resin. Subsequently, the coils are + U ₁ -U, -V, + V, + W, -W pushed in the cured state on the associated teeth 54.1 ... 54.6 and fixed. This procedure achieves a copper fill factor of more than 50%, resulting in a high power density with low inductance. For winding the coils, for example, a round wire with a diameter of 1 mm to 2 mm is used.

In the case of permanently excited linear motors, force fluctuations occur when, in the de-energized state, a magnetic flux density B _y does not assume a sinusoidal course in an air gap between primary part and secondary part.

A pole coverage ratio a = - describes the ratio of the magnetic bandwidth or the pole pitch b _p to the pole pitch or pole width τ _p . Preferably, the pile coverage ratio is 0.80 to 0.90. An approximately sinusoidal profile of the flux density B _y in the air gap between primary part and secondary part as a function of the position in the longitudinal direction L of the secondary part is then achieved (compare FIG. 3). The position of the secondary part relative to the primary part in the longitudinal direction L corresponds to an x-coordinate.

FIG. 6 shows the cutting impact damping device 36 in a perspective view. It can be seen that the first part primary part 50.1 and the second partial primary part 50.2 are connected on both sides via in each case one connecting element 60.1 or 60.2. Centrally between the sub-primary parts 50.1, 50.2, the secondary part 46 is arranged, which has on both sides of the permanent magnet 48 each have a T-shaped guide rail 62.1, 62.2. The guide rails 62.1, 62.2 have on their respective connecting element 60.1 or 60.2 sides facing a guide web 64.1 and 64.2 (not visible in Figure 6) with which they are mounted longitudinally displaceable on the respective connecting element 60.1 or 60.2. During operation of the linear motor, forces of up to 8,000 N arise between the primary and the secondary secondary parts. By virtue of the abutment of the secondary part described above, smaller forces can be absorbed by the guide rails 62 by a factor of 100.

FIG. 7 shows an exploded view of the linear motor 38. It can be seen that the permanent magnets 48.1... 48.12 are embedded in a matrix 66 of a nonconductor, namely of glass fiber reinforced plastic. Each permanent magnet has two broad sides, which are directly facing one of the two sub-primary parts 50.1 and 50.2. In other words, the two sub-primary parts 50.1, 50.2 share the permanent magnets. The linear motor 38 is also referred to as a double comb linear motor.

It can also be seen that screws 68.1 ... 68.4 engage through the longitudinal bores 58.1 ... 58.4 and are fastened to partial elements 70.1, 70.2 of the connecting element 60.1. Disposed laterally outside the first guide rail 62.1 is a displacement sensor 72, which detects the x-position of the secondary part 46 relative to the primary part 44 and forwards it to a schematically drawn electrical control 46. The electrical control 74 is also in contact with an acceleration sensor 76 schematically drawn in FIG. 2, which detects an acceleration of the plunger 16 and thus the upper tool. The electric controller 74 is also in contact with a servo inverter 78, which as Frequency converter works and is connected via not shown electrical lines with the coils + U ₁ -U, + V, -V, + W, -W in contact and these energized. The servo inverter 78 has a total power of 11, 2 kW. To carry out a method according to the invention, the plunger 16 (FIG. 1) is brought into a lifting movement along a repetitive lifting path. If the acceleration _sensor 76 detects an acceleration a, which is oriented _toward the table 24 or the lower tool 26 and exceeds a threshold value a _s , the corresponding point in time is set as the cutting start point t _e s.

The electrical control 74 controls the servo inverter 78 so that it energizes the coils + U, -U, + V, -V, + W, -W with a coil current Is _t rank (t), so that a restoring force F _Rü cksteiι (t) between the primary part 44 (Figure 2) and the secondary part (46) is formed. The restoring force F _Rüc k _ste iι (t) is chosen so that it is an oscillation Δx (t) of the plunger 16, ie the difference between the current position x (t) of the plunger 16 relative to its load-free stroke xiastfrei (t), counteracts. The load-free lifting path xiastfrei (t) is the path along the x-axis, which describes the plunger 16 as a function of time, if no workpiece is machined and therefore also no cutting stroke ensteht.

The servo inverter 78 is designed to provide a maximum string current per string of strings of Is _t rank = 29 A _D c. The application time of the servo inverter 78 is 380 μs with a time frame of 200 μs. The current Is _t r _a ng (t) through the coils + U, -U, + V, -V, + W, -W increases linearly to a good approximation and has reached a strength of Istrang = 29 A after two milliseconds. This results in a restoring force F _Rückst eiι (t) which also increases substantially linearly with time t and reaches 3 500 N after two milliseconds. In other words, a linear motor is preferred, which can a maximum restoring force F _R ücksteiι, max of more than 2 000 N, in particular more than 3000 N, can muster. The time, inside Half of this maximum restoring force is achieved, preferably less than 3 ms. The regulation of the linear motor 38 takes place in real time.

Since the cutting process is repeated periodically, it is possible to cut impact beginning t _Be beginning with high accuracy to predict. From a point of time t a head timing _pre-p _a nn, which is for example less than 500 ms, before the cutting impact beginning t _Be beginning is, the electric controller 74 controls the servo-inverter 78 on so that a biasing force F _vorsp ann to of the

Added force that applies the drive 14 to the workpiece. Immediately after the beginning of cutting stroke t _Be ginning then the restoring force F _return teiι is applied, which acts in a direction opposite to the biasing force F _vorsp ann.

FIG. 8 shows a schematic view of the dimensions of the cutting impact damping device 36 according to the invention. A primary part height of the partial primary parts 50.1, 50.2 is preferably less than 500 mm. A width of the partial primary parts is preferably less than 200 mm. Particularly favorable is a travel of less than 150 mm and more than 50 mm.

It is beneficial to provide two, three, four or more of the above described active cut impact attenuation devices on the plunger 16, particularly at its corners. So also oscillations of the swivel angle α, ß can be attenuated.

FIG. 9a shows a diagram which plots the tappet travel, ie the travel of the upper tool 28, as a function of the time t on the one hand for a movement without a cutting stroke and on the other hand for a movement with a cutting stroke. It will be appreciated that when a cutting stroke occurs, the plunger movement will make a vibration around the ideal path. The difference between the movement without a cutting stroke (which can be determined, for example, by moving the upper tool without a metal sheet) and the actual movement with a cutting impact is shown in FIG. 9b. FIG. 9b shows the oscillation Δx (t) thus determined as a function of the time t. From this oscillation Δx (t), an evaluation value B is calculated, in which the square is formed for the discrete measurement points t, at which the oscillation Δx was measured, and the squares are summed up. Then the root is drawn, giving the following formula for the score: B = / / ΣY'ΛΔXx «Cti) 2

;

FIG. 10 shows a lighting pattern 80 which has a number n of energizing intervals. All energizing intervals are equidistant in time and follow each other directly. In each Bestromungsintervall a certain voltage U is provided. Thus, for the first energizing interval from to to ti a voltage of U = 6VoIt is provided, which is applied to the linear motor. This means that the electrical control 74 (see FIG. 7) supplies the linear motor 38 (see FIG. 2) with the voltage 6 volts between to and ti. For example, the time to always corresponds to a crankshaft angle of 0 °. In a plurality of cuts so that the energization pattern for each cut through once. After an end time tε _hands. After the tool has left the sheet again, the evaluation value B is calculated from the oscillation Δx (t) (see FIG. Subsequently, the energizing pattern 80 (FIG. 10) is changed, for example by adding to each voltage value in the energizing pattern 80 a random voltage ΔU newly calculated for each value. The random voltages ΔU are shown in FIG. 11 in a random pattern 82. By adding the random voltages to the voltages of the energizing pattern 80, a new energizing pattern results, which is not shown. In a subsequent cut, the linear motor is supplied with this new current pattern. The result for the subsequent cut is an oscillation whose evaluation value B can be smaller or at least as large as the first evaluation value. If the second evaluation value is smaller than the first evaluation value, then the second irradiation pattern is more advantageous than the first energization pattern for suppression of the oscillation, and the second irradiation pattern is used as standard energization pattern for further cuts.

In subsequent steps as well, a respective newly generated random pattern is added to the respective standard current application pattern and accepted or rejected. In this way, the energizing pattern 80 converges over time against an ideal energization pattern in which the cutting impact is attenuated particularly efficiently. The larger the number n of the energizing intervals, the more effectively the cutting stroke can be damped. The smaller the number n of energization intervals, the faster the current flow pattern converges to a particularly suitable energization pattern. It has been shown that the two contradictory demands can be reconciled particularly well if the number n ranges between 50 and 100.

It is advantageous if a damping period 84 between the start of cutting impact -B _e beginning and the end time t _En de twice as long at most, as a lead-time 86 between the start time ts _t ar _t and the beginning of the cutting stroke t _SSE gi _nn - It should be emphasized that the evaluation value B usually tßeginn until the beginning of the cutting stroke is calculated.

With the method described, with a number n = 50 to n = 100 energizing intervals within 300 cuts, the friction travel that the cutting tool travels relative to the metal sheet can be reduced to less than one tenth. This also reduces wear by about a tenth.

Claims

claims:

A cutting method for reducing a cutting stroke of a cutting machine (10) having a cutting tool (30), comprising the steps of:

(a) moving a lower tool (26) and an upper tool

(28) of the cutting tool (30), between which a metal sheet is arranged, by means of a drive comprising a crank (14) towards each other,

(b) detecting a start of cutting impact (t _Be beginning)

(c) after the start of cutting (t _beg inn), at least one

Linear motor (38), so that a restoring force (FR _ücks teiι (t)) is applied to the cutting tool (30), which _{counteracts an} induced by the cutting shock oscillation (.DELTA.x (t)) of the cutting tool (30),

(as in DE 10 2008 011 024)

(d) the linear motor (38) starting at a given time point (tstart) up to a predetermined end time (tεnde) after the cutting impact beginning (t _Be gi _nn) in accordance with an energization pattern (80) is supplied with current corresponding to a standard current-sourcing .

(e) after the end time, calculating an evaluation value (B) from the oscillation (Δx (t)) of the cutting tool (30) representing a measure of a magnitude of the oscillation (Δx (t)) after the start of cutting (tβ start);

(f) changing the energization pattern (80) so that a second

Energizing pattern is obtained

(g) performing a second cut,

(h) calculating a second evaluation value of the oscillation (Δx (t)) of the cutting tool (30) after cutting start (t beginning) for the second cut, and (i) when the second evaluation value is smaller than the first evaluation value setting the second energization pattern as the standard energization pattern.

2. Cutting method according to claim 1, characterized in that the starting time (tstart) before the beginning of cutting stroke (t _Beg inn) is located.

3. Cutting method according to one of the preceding claims, characterized in that the Bestromumgsmuster corresponds to a set of time lent equidistant current or voltage values.

4. Cutting method according to one of the preceding claims, characterized in that the end time (t _En de) corresponds to the time at which the upper tool (28) comes out of engagement with the sheet.

5. Cutting method according to one of the preceding claims, characterized in that a lead time period between the start time (tstart) and the cutting start of shock (tbegin) at least a quarter of a damping period (84) between the cutting start of shock (t _B start) and the end time is long.

6. Cutting method according to one of the preceding claims, characterized in that

- detecting the beginning of the cutting stroke (t _Beg inn) and

the energizing of the at least one linear motor (38) is carried out at at least two, in particular at four, locations, wherein the at least two locations are arranged in particular at corners of the cutting tool (30).

7. Cutting method according to one of the preceding claims, characterized by the steps:

Detecting an angular position (α, ß) of the cutting tool (30) and

- energizing the at least one linear motor (38) so that the

Angular position (α, ß) of the cutting tool (30) approaches a desired angular position.

8. Cutting impact damping device for a cutting machine, characterized by

(a) a linear motor (38) arranged to act on a cutting tool (30) of the cutting machine (10),

(b) a cutting stroke start detecting device (76, 74) for detecting a cutting stroke start (t) and

(C) an electrical control (74) or control, which is adapted for carrying out a method according to any one of the preceding claims.

9. cutting impact damping device according to claim 8, character- ized in that the linear motor (38) is a double-comb linear motor.

10. Cutting impact damping device according to claim 9, characterized in that the linear motor (38)

- A permanent magnet having secondary part (46) and two oppositely disposed part-primary parts has, the partial primary parts, all permanent magnets share.

11. Cutting impact damping device according to claim 8 or 9, characterized in that the secondary part (46) has a matrix (66) made of server-reinforced plastic, in which the permanent magnets (48) are embedded.

12. Cutting impact damping device according to one of claims 10 or 11, characterized in that the secondary part (46) on both sides of a guide rail (62), by means of which the secondary part (46) is guided centrally between the two partial primary parts (50.1, 50.2).

13. Cutting impact damping device according to claim 12, characterized in that the guide rail (62) is ferromagnetic.

14. Cutting impact damping device according to claim 12 or 13, characterized in that laterally outside the guide rail (62) a Wegmesssensor (72), in particular a magnetic Wegmesssensor (72), for measuring a position (x) of the secondary part (46) relative to the primary part ( 44) is arranged.

15. Cutting impact damping device according to one of claims 8 to 14, characterized in that the secondary part (46) more

Teeth and has a toothed head winding with an open groove (56).

16. A cutting shock absorbing device according to any one of claims 8 to 15, characterized in that the secondary part (46) has six coils in the order + U, -U, -V, + V, + W, -W, each on separate teeth ( 54) act.

17. Cutting impact damping device according to one of claims 8 to 16, characterized in that the teeth of the secondary part (46) have a pole pitch (τp), and the permanent magnets have a Mag- net division (τ _M ), wherein the magnet division (τ _M ) substantially corresponds to 6/7 of the pole pitch.

18. Cutting impact damping device according to one of claims 8 to 17, characterized in that the cutting stroke start detection device comprises an acceleration sensor (76).

19. A cutting machine with a cutting impact damping device according to one of the preceding claims, wherein the cutting machine (10) is a high-speed cutting machine, which is designed for a

Stroke frequency of more than 100 strokes per minute.