EP0321602B1 - Gripper feeding device with pneumatically or hydraulically operated crank drives - Google Patents

Description

The invention relates to a gripper feed device with pneumatically or hydraulically driven crank drives, as known from EP-A-0033252.

As can be seen from the study of relevant specialist literature, the trend in the manufacturing industry today is moving away from mass production and towards a greater diversification of individual product groups, with a simultaneous decrease in lot sizes.
As is known, it is becoming increasingly necessary to make work and automation systems more flexible. When it comes to manufacturing simple parts with low quality requirements, this does not pose any major difficulties either.
With increasing quality requirements regarding dimensional accuracy and complexity, however, the automation effort also increases; but quickly reaches the limit of economy here. Especially in branches of production, such as non-cutting forming and here in particular punching technology, which have always had a high degree of automation. Since the possibilities for automation are relatively simple for technological reasons, it has become increasingly apparent after thorough studies that the known automation technologies have not kept pace with machine developments.
Absolutely new designs are therefore often necessary, because the ever further adaptation of existing technologies must ultimately lead to a dead end.

The aim of this invention is to present such a new construction and to justify its necessity.
It is a device of the type mentioned at the beginning for the automatic advancement of strip, strip or profile material in presses, punches or similar machines.

This development was initiated in addition to what was said at the beginning by the fact that the development of such a press, indicated by the "Differential Printing Press - Leinhaas" * prospectus, can only be automated using conventional automation devices available on the market with a major loss of the considerable existing technological advantage.
It will be shown here that the new designs mentioned, and here in particular the feed mentioned above, are not only in terms of their technology, but also in terms of cost, much cheaper than the laborious adaptation to existing technologies.
* December 1987 edition

In accordance with the requirements mentioned, there are only five applications in the publications of the German and European Patent Office, which however only partially touch on the problem described.

One of these applications, an American patent, dates from 1936 and relates to a double-pincer feed that is mechanically driven directly by the press, U.S. Patent 2,468,236.
In addition, four publications are described and their relevance examined.

a) DE-AS 1 265 106

It is a pneumatic double-clamp feed, in which each of the two clamps carries out a forward and return stroke using its own drive. A disadvantage here is the need for separate adjustment of both pliers, which affects the precision of the synchronization and also the enormous air consumption due to the use of two drive units.
However, the disadvantage of the separate setting can to some extent be turned into positives, since this system can now be used to run cyclically separate feed lengths, which in the narrower sense corresponds to the cycle program run of the full feed.

b) DE-OS 1 801 302

This publication describes a feed in which two pliers are attached to the opposite strands of a horizontally running roller chain.
This chain is cyclically driven by a reversible hydraulic motor, which in turn is powered by an electric motor-driven hydraulic pump.
This system is primarily intended for feed lengths greater than 1000 mm, where the use of hydraulic cylinders would be too expensive and designs with system-related idle stroke would require extremely long positioning times.

c) EP-A-0033252

This patent application describes a simple feed with only one movable pliers, which is not driven by a cylinder, but by an electropneumatic swivel module, which in turn rotates a crank arm adjustable in radius by 180 ° in or against the feed direction.
A sinuidal gear is used here to drive the feed tongs in order to achieve smooth start and stop.
Since the stroke adjustment on this device is carried out by presetting the crank radius, readjustment or readjustment of the feed length is only possible when the vehicle is stationary.
A further disadvantage is the fact that the drivable swivel device must perform a full rotation even with the smallest strokes, which, as already mentioned above, leads to an uneconomically high air consumption.

d) laid-open specification 0125367

This application, the most recent in the art, describes a feed that broadly summarizes the advantages of the three applications previously mentioned.
This is also a double gripper feed, the opposite movement of the gripper is generated by two eccentric discs. This is also intended to achieve particularly gentle starting and braking of the pliers. The stroke length adjustment of the feed tongs is done here, as under c), by a common presetting of the crank radii and is also only possible when the vehicle is stationary.
The cyclical swiveling movement of the eccentric discs by 180 ° is achieved in this system by a traction mechanism drive that wraps around both eccentric discs, one strand of which is correspondingly moved by the feed stroke by means of a pneumatic or hydraulic cylinder.
A disadvantage of this system, as already mentioned under c), is the impossibility of adjusting the stroke during the run and the fact that the driving cylinder must travel its full stroke even with small pliers strokes.
Another shortcoming of this system is the property that the maximum stroke length of each feed tongs is limited by the diameter of the driving eccentric disk.

After studying these publications, it is evident that the requirements outlined above for a modern feed system have not yet been satisfactorily met by a known construction.

In the following, the manufacturing process of automatic punching from the strip or from the strip will be described and examined in more detail.

The mechanical structure of an automatic punching system for processing tapes and strips is almost always the same.
It essentially consists of an unwinding device for the strip and the so-called reel, a straightening machine for straightening the strip that is curved due to the winding process, and a feeder, which is responsible for pushing the strip into the machine tool cyclically according to the press cycle.

• 1.) Positioniergenauigkeit des Werkstückes, also des Bandes oder Streifens,
• 2.) Positioniergeschwindigkeit für einen Takt und
• 3.) Taktfrequenz, um die Hubzahlen der Presse ausnützen zu können.

In addition to the press characteristics, the stroke in particular determines the quality and possible complexity of the part to be manufactured.
From this perspective, three basic requirements must be placed on the feed:

• 1.) positioning accuracy of the workpiece, i.e. the strip or strip,
• 2.) positioning speed for one cycle and
• 3.) Cycle frequency in order to be able to use the stroke rates of the press.

Further requirements arise when considering the corresponding application, eg clamping force of the belt.
It depends on the required acceleration and the mass or cross-section of the belt to be transported in order to ensure rapid advancement without slipping through the belt.

The tensile force of the feed is also important here, in order to pull a strip through the straightening machine depending on the cross section or curvature, provided that it does not have its own drive. Of course, the tensile force also influences the maximum transferable acceleration on the belt.

According to this requirement profile, the respective feed is selected according to the task of the system.

The functionality of the feed should now be examined in more detail:

Positioning accuracy:

• a) Taktwerkzeuge, mit denen während einem Pressenhub jeweils ein Teil direkt ohne Zwischenschritte vom Band gefertigt wird, und
• b) Folge- bzw. Folgeverbundwerkzeuge, in denen das jweils zu fertigende Teil mehrere umformtechnische Stationen durchläuft, um schließlich weitgehend fertig - also frei fallend - von der Maschine ausgeworfen zu werden.

Here again, a distinction must be made between two manufacturing technologies with regard to the tool.

• a) cycle tools, with which a part is produced directly from the belt without any intermediate steps during a press stroke, and
• b) Progressive or progressive composite tools, in which the part to be manufactured in each case passes through several metal-forming stations in order to finally be largely ejected from the machine - that is to say freely falling.

It is easy to see that positioning errors cannot have an additive effect on single-cycle tools, since only one complete forming process takes place per press stroke and possible positioning errors can only affect the economic use of the strip, as long as the positioning error is within the range of a pitch between two provided on the strip Workpieces.

With the follow-on or follow-on compound tool, however, positioning errors of the feed can have a striking effect on the part quality.
This quickly becomes clear when you consider that a workpiece is separated from the strip in several stations, but in one tool, eg perforated, bent, notched, corrugated, etc., and only at the end of the forming process.
Since the forming processes take place one after the other, they would have a strong influence on each other in terms of feed inaccuracies.

In terms of tool technology, the path is therefore followed by punching holes in the band in a first station or notching on the side of the band and then the band at the next press stroke, i.e. at the next forming station, using search pins or other types of stops positioned in the tool for the subsequent manufacturing processes.

So you shift the positioning accuracy from the feed to the tool. However, this in no way permits greater positioning tolerances of the feed, since the search pins or the side stops of the tool, if the pre-punched holes or notches do not lie exactly, can easily cause burrs or pinches on the belt when centering, which then because the belt is no longer in the Tool is movable, can lead to a loss of production, possibly under several hours.

In the case of progressive or progressive composite tools, it is also important that they must have a control-technical variant of the feed, when using the mentioned types of tools. This so-called intermediate ventilation means a brief, complete exposure of the belt in order to enable the tool-specific straightening devices to be positioned.

These positioning tolerances for the feeds range from 2/100 to 1/10 mm, depending on the feed system used.

When considering the path / time characteristics of differential path, differential pressure or eccentric presses, taking into account the total time for a stroke, it becomes clear what has already been mentioned in the introduction.
While a large part of the total stroke time is available for the feed process in the eccentric press, these time spans in differential travel and differential pressure presses have shrunk considerably due to the more favorable characteristics in terms of forming technology, with the desired simultaneous stroke sequence.

If these specified times are not adhered to, automatic operation is only possible to a limited extent on the press side, since the press must wait for the end of the feed process each time.
In addition to an undesired acceleration and braking process, this also results in a considerable time delay on the control side, since the switching processes of electrical, hydraulic or mechanical switching elements do not take place in an infinitely short time and usually add up.

One speaks here that the press does not come through.
On the feed side, the positioning speed can be influenced by the use of very fast controls, low-mass components and by a suitable damping system for the cyclically moving parts of the feed. Since the often insufficient positioning speed of conventional feeds, when used with modern press systems, often drastically reduce the theoretically possible number of cycles, special attention was paid to this point in the development of this invention.

In the brochures of relevant automation and feed device manufacturers, it is almost always only the cycle speed that is highlighted. However, it is only determined when the feed is running alone - i.e. without a press - so it does not take into account the deformation time of the press during which the feed is stopped.
They therefore often give a wrong picture of the performance of the respective feed device. Taking into account the need for a high actuating speed of the feed, as described above, high cycle rates of the feed result, of course, since the switching times of the feed control are usually not longer than the deformation time of the press.

To meet the problems described above, essentially two types of feed devices have prevailed to date.
These are on the one hand the pliers feed devices, in which the belt is clamped by means of movable pliers and these pliers are then moved towards the press during pushing use and away from the press during pulling use, and on the other hand the roller feed devices, with which the belt is between two oppositely movable rollers are clamped and pushed forward with one roller movement.

Another division can be made with regard to the drive.
A distinction is made here between feeds with their own drive and feeds from the press. With the latter, it is understandable that the best results can be achieved, since the feed follows the press characteristics directly.
However, their use is limited to eccentric or crank presses, since it is particularly easy to tap the press characteristics from the rotating eccentric shaft.
For high-speed punching with high-speed presses, only positively driven feeders are used, since the number of cycles around 1500 strokes / min. a synchronization between the press and feed cycle is no longer possible in terms of control technology.

The subject of this development, however, should be the feeds with their own drive.
They are now dealt with - divided into pliers and roller feeders.

As already mentioned, the band feed is carried out by the cyclic linear movement of the feed clamp which clamps the band. During the return stroke of the feed tongs, a fixed holding tongs now fixes the belt. In order to bring the feed tongs back to the starting position, clamp feeders have to carry out an idle stroke per cycle.

The feed tongs are driven by pneumatic or hydraulic cylinders, the pneumatics covering the range of smaller band widths, i.e. smaller tongs sizes up to approx. 250 mm and smaller feed strokes up to approx. 350 mm.
Hydraulic drives are used for tasks that exceed these values, since they can transmit larger forces and the pneumatics are uneconomical with regard to air consumption and actuating speed.
The clamping forces in the holding or feed tongs are also carried out pneumatically or hydraulically by means of short stroke or bellows cylinders, corresponding to the drive of the feed.

The stroke of the feed tongs is limited by one or two adjustable stops. The adjustment is usually divided into a coarse and fine adjustment and is only possible with most devices at a standstill.
Depending on the cost of the device, the stroke is displayed by simply measuring the stop position using a slide gauge, by means of attached scales with vernier and, in the case of particularly complex devices, by mechanical or electronic counting devices.

The greatest technical problem is the braking of the pliers in their end positions.
Pneumatic or hydropneumatic damping systems are used here, the damping strength of which is adjustable, but whose effective braking distance is always constant in relation to the stroke performed with the feed tongs.
Depending on the stroke length, sheet metal cross section and set lifting speed, it is necessary to adjust the damping to the new parameters each time using these damping systems. The inefficiency of such "energy destruction systems" becomes particularly clear when you consider that the damping unit not only has to brake the mass of the accelerated gun along the damping path,
but must also take up the work done by the drive, which works fully during the entire damping time.
Due to the system, this is unavoidable with conventional gripper feeders, since if the drive is switched off prematurely, it is not always ensured that the gripper will approach its end position precisely.

For the reasons described above and from the fact that the setting of the feed parameters can only be automated with a certain effort
in recent years, roll feed has often been given priority over pliers feed.

The system of the roll feed will now be explained in the following.

In roll feed devices, as already mentioned, the belt to be fed is clamped between two rolls, either one or both of which are driven, and advanced by the opposite movement of the rolls.
In the case of particularly large roller feeds, the drive is mainly carried out by hydraulic motors, in the case of smaller ones by the use of stepper motors, the rotation of which is usually transmitted to the rollers by low-mass toothed belt drives.

The structure in this form is much easier than that of the pliers feed.
Due to the principle of counter-rotating rollers, this type of feed is always in the start position, ie no return stroke is required. It is therefore also possible to run programs, for example, advance 10 mm, advance 20 mm and then advance 10 mm again, each during a press stroke.

The clamping between the rollers, which theoretically corresponds to a line, is often problematic.
This can lead to slippage of the belt at high rotational accelerations of the rollers or also to squeezing or imprints on the belt when transporting soft materials such as aluminum.
The above-mentioned ventilation, which is necessary when using follow-on tools, proves to be difficult to implement technically, i.e. exposing the belt for a short time between two feed strokes. Mechanisms such as control cams or pneumatic systems are used to briefly lift one of the two rollers.

The above-described effect of the formation of impressions on the tape is of course further enhanced by the re-installation of the roll.

The fact that it is not a matter of moving between two stops, but rather that the rollers are started and stopped freely, means that the positioning accuracy for roller feeders is significantly lower than that of pliers feeders. A possible slipping of the band will of course intensify this effect.

Despite these disadvantages, due to its ease of automation - no additional measuring or actuating element is required - the roll feed has become more widespread in recent years than the plier feed.
A new construction should now try to combine the advantages of both feed types described and to avoid their disadvantages as far as possible, especially from the point of view of flexibility mentioned at the beginning.

From the above, it can be seen, purely quantitatively, that the roller feed - when it comes to the technical advantages alone - is superior to the pincer feed.
However, it places significantly higher demands in terms of control, which in turn is often a disadvantage from an economic point of view.

If you now consider the advantages and disadvantages of the feed devices listed from a qualitative point of view, the role of roller feed shows
that the disadvantages with regard to precision and band clamping are system-related and therefore unavoidable.
Precision, however, is the fundamental factor that determines the applicability of machines, devices and tools in metal forming processes.
This deficiency has a particularly serious effect when the feed is used in the combination of the latest technology, such as the presses that work according to the differential pressure principle. Since these machines are primarily used for the production of particularly complex and high-quality parts, practically only clamp feeders are used, which in turn have their own disadvantages.

• 1.) Möglichst großflächige Bandklemmung, um das Band sicher und schonend, auch mit großen Klemmkräften, jedoch kleinen Pressungen, transportieren zu können.
• 2.) Vorschubbewegung ohne Auftreten von Leerhüben; der Vorschub muß sich nach ausgeführter Positionierbewegung wieder in Startposition befinden.
• 3.) Verringerung der erforderlichen Bremsleistung.
• 4.) Sanftes, möglichst ruckfreies Starten der Vorschubbewegung.
• 5.) Bei pnematischem Antrieb Vermeidung der Entstehung von Totvolumen durch die Vorschublängeneinstellung.
• 6.) Vorschublängenein- bzw.-nachstellung während des Betriebes möglich.
• 7.) Möglichst gedrängte, wenig ausladende Konstruktion.
• 8.) Vorschubbegrenzung durch voreinstellbare Anschläge, was eine größtmögliche Vorschubpräzision gewährleistet.

A combination of roller and pliers feed would ideally be suitable to solve the problems at hand, since the disadvantages of one system could be offset by the advantages of the other.
The solution to this problem, that is to say the combination of the advantages of roller and plier feed, is intended to be the real aim of this invention, the following requirements being given in more detail:

• 1.) As large a band clamping as possible, in order to be able to transport the belt safely and gently, even with large clamping forces but small pressures.
• 2.) feed movement without the occurrence of empty strokes; the feed must be in the start position again after the positioning movement has been carried out.
• 3.) Reduction of the required braking power.
• 4.) Start the feed motion smoothly and as smoothly as possible.
• 5.) With pnematic drive, avoidance of dead volume by adjusting the feed length.
• 6.) Feed length adjustment or adjustment possible during operation.
• 7.) As compact as possible, little protruding construction.
• 8.) Feed limitation through presettable stops, which ensures the greatest possible feed precision.

Taking this requirement profile into account, a purely qualitative search for solution principles must now be carried out.

A constructive pre-selection can already be made for this on the basis of the aforementioned criteria. The requirement for large-area clamping, for example, precludes the system of opposing rollers from the outset.
Furthermore, the demand for short operating times, i.e. high accelerations, which can only be achieved with drives that are extremely low in mass, leads to pneumatic and hydraulic units.

The two derived requirements - taken alone - correspond exactly to the scheme of the gripper feed described above.
Further considerations should therefore be made in this direction.

Taking into account the requirement for freedom from idle strokes leads from this aspect to the amazingly simple solution,
Two clamps, also in the feed direction, must be arranged one behind the other, but not only one but both clamps must be moved in opposite directions according to the feed cycle.
When the tool is at a standstill and closed, the pliers in the starting position take over the task of the previously fixed holding pliers. After the feed signal has been given, the closed gun moves forward and executes the feed stroke, while the second open gun runs back and is again in the start position after the cycle has been completed.

With the demands for the lowest possible air consumption and simple, also in the course of possible adjustment, a solution with two separate drive units for the two pliers is also excluded, since each drive would have to perform an idle stroke, which would increase the air consumption uneconomically and every drive would have to be equipped with its own stroke adjustment, which would violate the demands for simplicity and ease of use.
Furthermore, if two adjustment devices were used, it would not be guaranteed that both pliers have the same stroke length, which is essential for the function of a system with two movable pliers.

The pliers must therefore be connected to each other via a mechanical system and set in motion by a drive.
To meet the demands for jerk-free acceleration and reduction of the drive power in the range of the set end position of the feed tongs, the use of an articulated drive of whatever type in the drive system of the feed offers itself.
The search for control technology solutions is abandoned from the outset, since on the one hand they would probably not prove to be responsive enough, on the other hand they would be too expensive when using a hydraulic drive, and even when using a pneumatic drive because of the compressibility of the air would be impossible to point out.

• 1.) Zwei in Vorschubrichtung hintereinander angeordnete gegenläufige Vorschubzangen.
• 2.) Mechanisch zwangsläufige, möglichst formschlüssige Kopplung zwischen den beiden Zangen.
• 3.) Zentraler pneumatischer Antrieb;
  der Pneumatik wird hier gegenüber der Hydraulik der Vorrang gegeben,
  da ein eventuell zu erstellender Prototyp aus Kostengründen zunächst nur kleinere Abmessungen haben soll, was zur Erprobung des Systems vollkommen ausreichend ist.
• 4.) Beschleunigungscharakteristik durch Verwendung eines Gelenktriebes in Form einer trigonometrischen Funktion.

After these considerations, a picture of the system to be created is already emerging:

• 1.) Two opposing feed tongs arranged one behind the other in the feed direction.
• 2.) Mechanically inevitable, preferably form-fitting coupling between the two pliers.
• 3.) Central pneumatic drive;
  pneumatics is given priority over hydraulics,
  Since a prototype that may be created should initially only have smaller dimensions for cost reasons, which is completely sufficient for testing the system.
• 4.) Acceleration characteristics by using an articulated drive in the form of a trigonometric function.

The solution to the overall problem according to the invention provides that
that the two collets, which are each guided in guides on both sides, and these are positively connected on the drive side by the two racks fixed to them and the intermeshing, rotatably mounted pinion,
that when the pinion is rotated in direction a, the two pliers execute a movement towards one another,
that when the pinion is rotated in direction b, the collets move away from each other in direction b1, the cyclical pivoting movement of the pinion being converted into a cyclically opposed collet movement by the toothed racks arranged opposite one another,
that the pressure rollers are assigned to the sides of the racks facing away from the tooth in an adjustable alignment with the pinion,
that the pinion is driven via a shaft a gear stage by the cyclical following a sinuidal function, in connection with the crank disc, and this by a pressure cylinder, the piston rod of which is pivotally connected to the crank pin mounted on the crank disc, the rectified cylinder tube of which is a common pivoting movement , When changing the piston rod, the bearing pin is carried out, which in turn is mounted in an adjustment slide that is independent of the function of the system and, coaxially opposite the bearing pin, is provided with another bearing pin, and this via the push rod with the bearing pin one on the Main shaft, regardless of its rotational movement, is connected to a movably mounted adjusting disk,
that the crank disk is at a distance on the same radius is provided with a second crank pin which is articulated via the piston rod and a cylinder drive to the pin of the collet, and
that the crank disk has on its periphery a cam directed towards its center, which actuates an independently arranged switch for reversing the two cylinders.

The summary definition of the essential characteristics of the request for protection allows the creation of a clamp feeder that meets the main requirements of the task.

In addition to the gear stage, it is stated that the main shaft and the shaft driving the pinion can be driven in a step-down manner by a connecting or intermediate gear stage, it being provided that the gear stage is formed by a chain or belt drive.

To determine the stroke length, it is noted that this is determined by adjusting the position of the bearing pin of the adjustment slide relative to the crank pin of the crank disk projected in the same plane via the pressure cylinder and its piston rod, the adjustment range being limited by the usable stroke of the piston rod in the pressure cylinder. The question of how the recruitment or by what means this is done will be commented on later in the description.

Regarding the arrangement of the two cylinders, it is noted that they are arranged on the crank disk and on a collet in such a way that when the piston rod returns in the direction of the collet, the torque to the cam disk axis towards the end position decreases more strongly.
and the respective retracting cylinder has the function of a damping cylinder.

To adjust the stroke length, it is proposed that the adjusting disk, which is rotatably arranged on a bush on the shaft, is assigned a second disk, the periphery of which is equipped with worm teeth, into which a worm engages and, when the worm rotates, the bearing journal arranged on the periphery of the adjusting disk its position changes, and thus the distance between the main shaft and the collet can be changed via the bearing pin provided on the pliers side, and that this change also changes the distance between the crank pin and the pin via the piston rod and the cylinder.

The invention is fully disclosed by these further or supplementary measures.

For the sake of a better overview and to enable comparisons to be made with the conventional roller or gripper feed devices, the advantages of the system according to the invention are to be worked out again here.

Large-area clamping with collet, which enables the transfer of high clamping forces with low pressure. This ensures that the belt is clamped securely, while at the same time protecting the belt as much as possible.

Cyclic counter-rotating pliers movement, with one of the pliers in the start position. An idle stroke is not necessary.

Both pliers are moved by one drive, which ensures synchronous pliers movement with a short overall length of the overall system. Optimal positioning accuracy due to the movement between two stops.

The feed play adjustment or readjustment option is made possible by changing the toothing distance between the pinion and the rack.

Even in the case of designs with large strokes, only small flywheels, that is to say small turning masses, are required, since only the reduction of the transmission element connected downstream of the drive unit has to be changed.
To obtain the same feed forces, only a drive cylinder with a larger piston cross-sectional area but the same stroke length would have to be installed.

Lowest air consumption since the drive cylinders start from their end position regardless of the feed length setting.

The braking power is greatly reduced due to the fact that the accelerating forces or moments continuously decrease towards the end of the stroke.

With the stroke length setting, the braking distance is automatically changed by positively driven cams. This means that little or no adjustment of the damping strength to the new stroke conditions is necessary.

In extreme applications, the possibility of considerably increasing the feed force by pressurizing the pressure chamber of the cylinder on the piston rod side.
The stroke adjustment or readjustment is easily possible during the run. This considerably simplifies setting up and monitoring the machine.
Good access to all components for assembly and maintenance purposes thanks to frames that are open on both sides.

Figur 1 zeigt

das Antriebsschema des Vorschubs in der Seitenansicht.

Figur 2 zeigt

die Draufsicht mit den beiden Spannzangen, die in den beidseitigen Führungen verschiebbar sind.

Figur 3 zeigt

das Funktionsprinzip des Antriebes und der Verstellvorrichtung in getrennter Darstellung.

Figur 4 zeigt

die Antriebseinheit mit gegenüber Figur 3 verringerter Hublänge.

The gripper feed device according to the invention is explained in more detail by the drawings of an exemplary embodiment.

Figure 1 shows

the drive diagram of the feed in side view.

Figure 2 shows

the top view with the two collets that can be moved in the guides on both sides.

Figure 3 shows

the functional principle of the drive and the adjusting device in a separate representation.

Figure 4 shows

the drive unit with a reduced stroke length compared to FIG. 3.

The collets 1 are shown in their outer end position with solid lines and in their inner end position with broken lines (Figure 1).

The collets 1 are guided on both sides in the guides 2. Both collets 1 are positively connected on the drive side by the two racks 3 fixed to them and the rotatably mounted pinion 4. When the pinion 4 rotates in the direction a, the two pliers now perform a movement a 'towards one another. When the pinion 4 rotates in the direction b, the collets 1 move away from one another in the direction b '.
The cyclical pivoting movement of the pinion 4 is thus converted into a cyclical counter-rotating pliers movement by the racks 3 arranged opposite. In order to be able to adjust this drive arrangement in accordance with the required feed tolerance without play, the pressure rollers 5 are adjustably assigned in alignment with the pinion 4 on the side of the rack 3 facing away from the tooth.

The pinion 4 already described is now driven by the main shaft 8 via the shaft 6 and the step-down gear stage 7 - shown here as a belt drive. The cyclic — a sinuidal function — rotary movement of the shaft 8 is generated by the crank disk 9 firmly connected to it.
Position 10 shows one of the driving pneumatic or hydraulic cylinders,
whose piston rod 11 is pivotally connected to the crank pin 12 mounted on the crank disk 9 and the cylinder tube of which can also perform a pivoting movement around the bearing pin 13.

If pressure is applied to the cylinder 10.1 on the side of the piston facing away from the piston rod 11, the crank disk 9, driven by the piston rod 11.1 and the bearing journal 12.1, performs a rotary movement in direction a.
The cylinder 10 is returned to its starting position via its piston rod 11 and the crank pin 12 until the piston strikes the rear wall of the cylinder again.
At the next stroke, the cylinder 10 is again pressurized and the cylinder 10.1, which has previously been extended, is returned to its starting position, the crank disc 9 now executing a rotary movement in direction b.
The end position of the drive unit shown clearly shows that the torque generated by the cylinder with respect to the cam axis towards the end position is reduced more and more.
This reduces the braking power to be applied by the respective retracting cylinder, which has the function of a damping cylinder. In this system, the throttle function of the respective retracting cylinder is to be switched on via a cam 20 mounted centrally between the bearing journals 12 and 12.1.
which triggers a switch 21 each time it passes through the center line of the crank disk 9 shown here horizontally.
Since the cylinder movement takes place alternately symmetrically, the cam 20 always runs past the switch 21 regardless of the stroke setting after the respectively set half rotation of the crank disk 18.
The length of the braking distance is therefore not always constant, as is the case with conventional feed devices, but corresponds to half a feed length.

The adjustment of the feed length or the adjustment of the swivel angle of the adjusting disk 18 should take place in that the collet 1,
on which the two cylinders 10 and 10.1 are articulated by means of the bearing journal 13 and 13.1, are displaced in the direction of the adjusting disk 18 when the feed length is reduced or, when the feed length is increased, are moved away from it. Since a movement of the adjustment slide 14 is not required for the functioning of the system, an adjustment of the stroke length in the barrel is possible without any problems.

From Figure 4 it can be seen that the piston of the cylinder 10.1 already reaches its end position after a significantly shorter stroke of the cylinder 10.

Since the pistons of the drive cylinder, regardless of the stroke length set, start from their end position, there is no dead volume due to the adjustment, which would have to be pressurized each time using pneumatic cylinders and would thus increase the air consumption uneconomically.
Another advantage of this drive system results from the use of two opposing, independent pressure medium cylinders.
If particularly high feed forces are desired, the cylinders can also be pressurized on the piston side facing the piston rod.
When using hydraulic cylinders, this property enables a particularly small and compact drive system with very high feed forces.

The kinematic equation of motion of the drive system can be derived from the equation of the offset crank drive known in technical mechanics.

The adjusting disk 18 is connected to the adjusting slide 14 by means of the bearing bolts 15 and 17 and the connecting rod 16 connecting them. With a corresponding rotation of the adjusting disk 18, the adjusting slide 14 now moves,
depending on the direction of rotation, towards or away from the crank disc.
If the pull rod 16 is now arranged in any plane parallel to one of the driving cylinders, adjusting the adjusting disk 18 by a few degrees results in the same change in the swing angle of the crank disk 9.

If you consider that the maximum swing angle of the crank disc 9 is determined by the position of the trunnions 12 and 12.1 in their end or starting positions, and that the trunnion 17 exactly, only displaced in parallel, represents this position, the linear dependence of set angle of the adjusting disk 18 clearly from the set swing angle of the crank disk 9.

Viewed from a mathematical point of view, the movement function imposed by the adjusting disk 18 and the adjusting slide 14 exactly represents the movement characteristic according to which the distance s has to be changed in order to achieve a linear adjustment.

The distance between the main shaft 8 and the pins 13 and 15 of the adjusting slide 14 arranged parallel to this on an axis is shown.

In conclusion, the following should be noted:

1 shows a possible solution in such a way that the adjusting disk 18 is not mounted next to, but above the crank disk 9, as shown in FIG. 3 or FIG. This enables a more compact solution.

The compact design of this solution principle is also illustrated in FIG. 1.
The overall length is determined exclusively by the collet stroke and is no longer than in conventional collet feeders, where the space for the second collet shown here would be required by the driving cylinder. Furthermore, it is possible to make the frame 19 open on both sides for better accessibility during assembly and maintenance work.

Claims (6)

1. A gripper feeding device with pneumatically or hydraulically operated crank drives, characterized in
   
   that the two clamping grippers (1) are respectively guided, on both sides, within guides (2), and, on the drive side, are movably connected, in form-locking manner, by the two gear racks (3) respectively rigidly mounted thereon and the rotably disposed pinion (4) in engagement therewith,
   
   that upon rotation of the pinion (4) in one direction (a), both grippers (1) move toward one another in direction (a1),
   
   that upon rotation of the pinion (4) in the opposite direction (b), the clamping grippers (1) move away from one another in direction (b1), with the cyclical swivel movement of the pinion (4), through the oppositely disposed gear racks (3), being converted into a cyclically countercurrent movement of the grippers,
   
   that adjustably associated to the sides of the racks (3) facing away from the gears, in alignment with the pinion (4), are the pressure rolls (5),
   
   that the pinion (4) is driven, through shaft (6), by a gear step (7) by the rotating movement cyclically following a sinusoidal function in conjunction with the crank cam (9), with the latter being connected by a pressure cylinder (10) the piston rod (11) of which is pivotably disposed on the crank cam (9), to the crank pin (12), with the rectified cylindrical tube thereof performing a common swivel movement upon a change in the piston position about the bearing pin (13) which, in turn, is disposed in an adjusting sledge (14) independent of the function of the system and, while diposed coaxially opposite the bearing pin (13), is provided with another bearing pin (15), with the latter being connected, through the push bar (16), to the bearing pin (17) of an adjusting disc (18) movably disposed on the master shaft indepently of the rotating movement thereof,
   
   that the crank cam (9) disposed in spaced relationship on the same radius, is provided with a second crank pin (12.1) which, through the piston rod (11.1) and a cylindrical drive (10.1) is hinged to the pin (13.1) of the clamping gripper (1), and
   
   that the crank cam (9) at the periphery thereof comprises a cam (20) directed toward the center thereof, which cam (20) actuates an independently disposed switch (21) for the changeover of the two cylinders (10 and 10.1).
2. A gripper feeding device according to claim 1,
   characterized in
   
   that the master shaft (8) and the shaft (6) driving the pinion (4), through a connecting or interposed gear step (7), are actuable in speed-reducing manner.
3. A gripper feeding device according to claim 2,
   characterized in
   
   that the gear step (7) is formed by a chain or belt drive.
4. A gripper feeding device according to claims 1 and 2,
   characterized in
   
   that the stroke length by adjusting the position of the bearing pin (13) of the adjusting sledge (14) relative to the crank pin (12) of the crank cam (9) projected in the same plane is determined through the pressure cylinder (10) and the piston rod (11) thereof, with the range of adjustment being limited by the useful stroke of the piston rod (11) within the pressure cylinder (10).
5. A gripper feeding device according to claims 1 to 4,
   characterized in
   
   that the cylinders (10,10.1) are so located on the crank cam (9) and on the clamping gripper (1) that with the piston rod (11) or (11.1) being withdrawn toward the clamping gripper (1), the momentum to the cam plate axis is reduced to a higher degree toward the end position, and the respectively retracting cylinder has the function of a dashpot.
6. A gripper feeding device according to claim 1,
   characterized in
   
   that associated to the adjusting plate (18) disposed on a sleeve in a manner rotatable on shaft (8), is a second plate the periphery of which is furnished with a worm gear engaged by a worm and, upon rotation of the worm, the bearing pin (17) disposed on the periphery of the adjusting plate (18) changes its position so that, through the bearing pin (15) provided on the gripper side, the distance between the master shaft (8) and the clamping gripper (1), through the push rod (16) is variable, and
   
   that in view of that change, the distance between the crank pin (12) and the pin (13), through the push rod (11) and the cylinder (10), equally, undergoes a corresponding adjustment.

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