EP0527414B1 - Blind-rivet tool - Google Patents

Abstract

The blind-riveting tool has a puller mechanism with grip moved by an electric motor via a gear train. The velocity ratio of the gear train (9 - 16) is independent of the position of the puller mechanism (4), and forms a permanent coupling between the motor (5) and the matter. Puller mechanism movement is controlled solely by the motor. The gear train can incorporate balls working between a screwed spindle (16) and a nut (15), the latter having external teeth and being driven by the motor, while the former is coupled to the puller mechanism.

Description

The invention relates to a blind riveting tool with a housing and a pulling device having a gripping mechanism, which can be moved by an electric motor via a gear device, according to the introductory part of claim 1.

Such a blind riveting device is known for example from US-A-3095 106.

US 3 095 106 describes a blind riveting device which generates the longitudinal movement of the pull rod with the aid of a spur gear and a ball screw. Here, the spindle is driven. The reset takes place after disengaging a clutch via a return spring.

In the case of a blind riveting device as is known from EP 116 954 B1, the rotational movement of the electric motor is transmitted to a rack-like pull rod with the aid of a gearwheel-like drive pinion. The drive pinion has three teeth that are evenly distributed over the circumference. The pull rod has a protruding tooth. The drive pinion now grips one of its teeth in front of the tooth and axially moves the pull rod when it rotates further. A gripping mechanism arranged at the front end of the pull rod pulls the mandrel of a blind rivet. According to a predetermined Angle of rotation of the drive pinion slides from the tooth of the pull rod. The pull rod is transported back to its starting position by the force of a spring. This arrangement has several disadvantages. On the one hand, the transmission ratio of the drive pinion-drawbar gearbox is dependent on the position of the drawbar. The translation is the worst at half the movement of the pull rod, in which the mandrel is normally to be torn off, that is to say the highest pulling force is required, since the worst case is the leverage ratio. The motor has to apply a relatively large torque, which leads to an increased power requirement. Furthermore, the motor not only has to exert the force to set the blind rivet and tear off the mandrel, it also has to work against the force of the return spring, which increases with increasing displacement of the drawbar. If the mandrel has not yet been torn off by the end of the movement of the pull rod, the tooth of the drive pinion slides out of the pull rod under full load, which is a very critical and highly wear-promoting state. In addition, in this case, an unpleasant vibration in the device is also noticeable externally, which an operator perceives as a blow in the hand holding the device. So that the device can assume its initial position, i.e. is able to accept a new blind rivet, the full stroke of the drawbar must be traversed every time, even if the setting process of the blind rivet has already ended. These unnecessary movements of the electric motor cause additional electricity consumption. The sudden resetting of the pull rod caused by the return spring also causes a relatively large amount of noise. Here, too, uncomfortable vibrations are caused. The known blind riveting device can be operated with batteries or accumulators. If the voltage of the battery drops so far during the setting process of a blind rivet that the mandrel of the blind rivet can no longer be torn off, it is provided in a special embodiment that the electric motor can be reversed in order to push the pull rod forward and thus the gripping mechanism from the mandrel to loosen the blind rivet.

US 3,375,883 and US 3,127,045 show further blind riveting devices in which the rotary movement of the electric motor is converted into a linear movement of the pull rod with the aid of a connecting rod drive. If necessary, the connecting rod drive is connected to the permanently running electric motor by means of a coupling. A disadvantage of this principle is that half of the possible stroke of the drawbar has the most unfavorable leverage ratios. Since the mandrels are torn off at this position of the pull rod, an engine power is required which, despite the unfavorable transmission ratios, provides sufficient torque to cause the mandrel to tear. This makes the device heavy, which leads to operator fatigue even with short operating times. A large amount of energy is also required.

The invention has for its object to provide a blind riveting tool that enables more comfortable and energy-saving work.

This object is achieved in a blind riveting device of the type mentioned in that the transmission device has a transmission ratio which is independent of the position of the pulling device and forms a permanent operative connection between the electric motor and the pulling device, the movement of the pulling device taking place exclusively under the control of the electric motor.

The blind riveting device according to the invention therefore does not require a return spring. The power of the electric motor must only be used to pull the mandrel of the blind rivet to be inserted into the blind rivet and later to tear it off. Since the transmission device has a transmission ratio that is independent of the position of the traction device, the electric motor only has to be dimensioned so large that it can apply the necessary breaking torque at the given ratio. The motor can therefore be made smaller and therefore lighter than in the known devices. Since no return spring is provided, the pulling device is reset via the electric motor, which is reversible for this purpose. The reversibility of the motor enables the traction device to be moved back to the starting position from practically any position. This avoids unnecessary movements of the pulling device, such as going through the full stroke. Since the tie rod and the electric motor are permanently connected to each other, the electric motor does not move can do without the drawbar is also moved, this means that the electric motor does not have to make any unnecessary movements. Energy is therefore only required for the desired and necessary movements of the pull rod. This makes the blind riveting tool particularly advantageous if a battery or an accumulator is used as the electrical energy source. In this case, efforts are made to keep the current consumption as low as possible, in order to ensure that the work is as long as possible by charging the batteries or using a set of batteries. Since the motor and the tie rod are permanently in engagement with one another via the transmission device, there are also no sudden movements which could reduce the comfort for the operator during operation.

In a preferred embodiment, the gear mechanism has a ball screw drive with a nut and a spindle. Ball screws convert a rotating movement, ie the rotary movement generated by the electric motor, into a linear movement that is required for the traction device, similar to trapezoidal screws, but they have a much higher efficiency. Ball screws are reversible, ie the traction mechanism can move in both directions. Above all, a ball screw drive is a well-suited example of a gear device for converting a rotary into a translatory movement, in which the transmission ratio is independent of the position of the pulling device.

It is preferred that the nut is driven and the spindle is connected to the pulling device. The overall length can thereby be kept smaller than in the reverse case, which is known from US 3,095,106, since in the reverse case the overall length of the ball screw nut must be increased by at least the maximum possible stroke of the spindle.

The nut preferably has external teeth. Another toothed wheel can mesh with the external toothing, i.e. a toothing on the outer circumference. Since the nut has a larger outer diameter than the spindle, this results in a larger lever, which can be advantageously used. The motor can be designed with a weaker torque.

In a particularly preferred embodiment, the spindle is hollow and forms a mandrel disposal path connected to the gripping mechanism. The mandrels of the blind rivets to be set therefore no longer have to be disposed of to the front, from where the next blind rivet is to be inserted, they can also be disposed of through the mandrel disposal path to the rear, i.e. through the blind riveting device. This allows for very fluid work since the time otherwise required to dispose of the mandrel released by the gripping mechanism can already be used to insert the mandrel of the next blind rivet.

A tube is preferably arranged in the housing and extends telescopically into the end of the spindle facing away from the gripping mechanism, the spindle being axially movable relative to the tube. The thorn disposal path has a variable length. It extends from the gripping mechanism to the end of the tube. The further the gripping mechanism is moved in the direction of the tear-off position of the mandrel, the shorter the mandrel disposal path becomes. This has the advantage that the overall length of the device does not change during operation. It remains constant with the length that the device has in "idle". This enables work even in confined spaces without having to forego the advantage of thorn disposal to the rear.

The housing advantageously has a mouthpiece which is supported on the nut via an axial bearing. The mouthpiece serves as a contact surface for the blind rivet if the blind rivet is to be placed by pulling on the mandrel. Due to the fact that the mouthpiece is supported directly on the nut, the opposing forces that occur when the mandrel is pulled are derived directly from the parts that generate the force. Only these parts must be dimensioned sufficiently to withstand the tensile forces. The remaining part of the housing can be dimensioned weaker, so it can be made lighter. On the one hand, this results in considerable weight savings. On the other hand, this also reduces the manufacturing effort.

Advantageously, the mouthpiece is also connected to a cage which at least partially encompasses the mother and which is supported by a second axial bearing on the side of the mother facing away from the mouthpiece. If the electric motor is reversed and the spindle returns to its starting position, forces are exerted on the spindle again at the end of the return stroke, to open the gripping mechanism. These forces are considerably lower than the forces required to tear off the mandrel. However, by using the second axial bearing, these opening forces are also transferred back to the ball screw nut, so that the entire remaining housing remains almost free of forces. The only forces that the housing has to absorb are the bearing forces for the rotational movement of the ball screw nut and a gear wheel driving it. The entire setting mechanism, i.e. the pulling device with gripping mechanism, the mouthpiece and the ball screw drive, can then be manufactured as an interchangeable unit. Measures to transfer larger forces from there to the other parts of the housing do not have to be taken, since this unit absorbs all forces when the rivet is set.

A stop is preferably arranged on the spindle, at least for one direction of movement, which comes into contact with the nut after a predetermined axial movement of the spindle. This stop prevents the spindle from being screwed out of or into the nut so far that it comes into contact with housing parts in such a way that impermissibly high forces are exerted on these housing parts. The forces generated by the ball screw are already absorbed by the stop. This also makes the housing relatively easy to carry out, which increases the ease of use. A largely fatigue-free work is possible.

In a particularly preferred embodiment, which, if necessary, can also be used with a position-dependent transmission ratio and without a permanent operative connection, the electric motor is preceded by an electrical circuit arrangement with an actuation switch, which switches the electric motor in one direction when the actuation switch is actuated and in the other after the actuation has ended Direction drives. This embodiment enables particularly simple work. When the operator wants to place the rivet, he inserts the rivet mandrel into the blind riveting tool and brings the blind rivet to the intended location. Then the operating switch is operated. The electric motor now drives the pulling device in one direction until the mandrel of the blind rivet breaks off. Since a further movement of the traction device is no longer necessary, the operator releases the actuation switch. The operation is now finished. The circuit arrangement now automatically reverses the motor and thus brings the pulling device back to its starting position, where the old mandrel can be disposed of and a new blind rivet inserted.

It is preferred that the circuit arrangement briefly short-circuits the electric motor when the actuation switch is actuated. By short-circuiting the electric motor, the motor is braked without a counter voltage acting on it. This keeps the electrical and mechanical load on the motor low.

The circuit arrangement preferably has at least one controlled switch, the control signal of which can be influenced by the actuation switch. The actuation switch does not directly switch the motor currents. It only switches control signals. As a result, the operating switch can be kept small. The operator then only has to exert slight forces to operate it.

It is preferred here that the controlled switch is assigned a delay device which delays the actuation of this switch by a predetermined period of time. This delay can be used, for example, to generate the short circuit which is preferred for braking the motor.

The advantage here is that the time period is in the same order of magnitude as the stopping time of the unloaded, short-circuited electric motor. It is therefore ensured that the electric motor has come to a standstill before it is reversed. So it can not happen that the motor suddenly receives a counter voltage in full speed. This protects the mechanical parts, e.g. Bearings and gears, which can be dimensioned accordingly small and light.

Preferably, two controlled switches designed as changeover switches are provided, which together switch two different short-circuit circuits. The electric motor can then be short-circuited from any direction of movement without the need for major circuitry measures.

It is also preferred that at least one limit switch is provided which can be actuated by the spindle and which interrupts the energy supply to the electric motor. Such a limit switch prevents the spindle from being moved beyond a predetermined position and pressing against the housing, which could damage the housing. Such a limit switch can be provided as an alternative or in addition to the stops on the spindle.

It is also preferred that the limit switch deactivates the delay device when actuated. In the end position, the motor should not be reversed, which would be caused by the controlled switch. Only the motor should be braked here, for which the direct actuation of the switch is sufficient.

The limit switch advantageously switches the control signal. The limit switch can therefore also be made correspondingly small, since it has practically no power, but only has to switch signals.

The circuit arrangement advantageously has an overload protection. This switches off the energy supply to the motor if the motor draws too much current, for example due to a torque that is too large. This protects the motor from overloads.

Fig. 1

eine Querschnittsansicht eines Blindnietgeräts,

Fig. 2

eine Schnittansicht einer Zugeinrichtung,

Fig. 3

eine Detaillansicht des hinteren Endes des Blindnietgeräts,

Fig. 4

einen Schnitt IV-IV nach Fig. 3 und

Fig. 5

eine Schaltungsanordnung.

The invention is described below with reference to a preferred embodiment in conjunction with the drawing. In it show:

Fig. 1

2 shows a cross-sectional view of a blind riveting device,

Fig. 2

2 shows a sectional view of a traction device,

Fig. 3

a detailed view of the rear end of the blind riveter,

Fig. 4

a section IV-IV of Fig. 3 and

Fig. 5

a circuit arrangement.

A blind riveting device 1 has a pulling device 4, which is described in more detail in FIG. 2. The traction device 4 is arranged together with a drive motor 5, which is designed as an electric motor, in an outer housing 2. The outer housing 2 can, for example, consist of two plastic shell halves constructed essentially symmetrically to one another. An accumulator 6 or a battery for supplying power to the motor 5 is arranged in the outer housing 2. Furthermore, there is an actuating switch 7 with an actuating element 37 in the outer housing 2 and, electrically connected between the accumulator 6 and the motor 5, a circuit arrangement 8 described in connection with FIG. 5.

The motor has an output pinion 9, which meshes with a spur gear 10 of larger diameter. This spur gear 10 is rotatably connected to a gear shaft 11, which in turn is rotatably supported in bearings 12 in the outer housing 2. At the other end of the gear shaft 11 there is again a pinion 13 which has a smaller diameter than the spur gear 10. The pinion 13 meshes with an external toothing 14 a ball screw nut 15. The ball screw nut 15 is in turn rotatably mounted in a bushing which is fixedly arranged in the outer housing 2.

The ball screw nut 15 rotates on a spindle 16. The spindle 16 is secured against rotation by means of torque supports 17, which can be designed as needle bearings and are guided in guideways 18 in the outer housing 2. When the ball screw nut 15 rotates, which is brought about by the motor 5 via the pinions 9, 10, 13 and the external toothing 14 of the ball screw nut 15, the spindle 16 moves axially.

A gripping mechanism 3 is arranged at one end of the spindle 16, hereinafter referred to as the "front end". The gripping mechanism 3 has clamping jaws 19 which are conical on the outside, the thinner diameter of the cone pointing forward. The clamping jaws 19 are surrounded by a chuck housing 20 which has a corresponding inner cone. At the rear end of the clamping jaws 19, a pressure piece 21 is arranged, which is supported on the spindle 16 via a compression spring 22. The clamping jaws 19 project forward over the chuck housing 20 here. When the spindle 16 is moved into the front end position, the clamping jaws 19 come to rest against a mouthpiece 23. They then follow up against the force of the compression spring 22 moved behind. This brings them into an area with a larger diameter of the inner cone of the chuck housing 20, as a result of which the clamping jaws 19 open. If, on the other hand, the spindle 16 is moved in the other direction, the clamping jaws 19 are removed from their stop. The compression spring 22 presses the clamping jaws 19 forward out of the chuck housing 20 connected to the spindle 16 via the pressure piece 21. The diameter enclosed by the clamping jaws 19 is reduced. An unillustrated mandrel of a blind rivet is then held. The process of setting a blind rivet per se is known for example from EP 0 116 954 B1, to which reference is hereby made. If the clamping jaws 19 do not protrude forwardly from the chuck housing 20, it can also be provided that the mouthpiece 23 has a rearward protruding projection against which the clamping jaws 19 can come to rest.

The mouthpiece 23 is mounted on an inner housing 24 on a thrust bearing 25 which is designed as a thrust bearing and which is supported with its other side on an end face of the ball screw nut 15. The force exerted by the spindle 16 on the blind rivet, not shown, is thus absorbed directly by the ball screw nut 15 without the relatively high compressive forces, which correspond to the tensile forces required to tear off the mandrel, to be absorbed by the outer housing 2. The outer housing 2 must therefore only be dimensioned to such an extent that it can absorb the torques which are necessary for the rotational movement of the pinion or the ball screw nut 15. On the same thrust bearing 25, a stop 26 is supported against which one part of the chuck housing 20 projecting over the diameter of the spindle 16 comes into contact when the spindle 16 has been moved into its extreme rear end position. A further axial displacement of the spindle 16 is blocked by the stop 26 without the outer housing 2 having to absorb the forces necessary for the blocking. These are passed directly to the ball screw nut 15 via the thrust bearing 25.

Furthermore, a cage 27, which at least partially encompasses the ball screw nut 15, is provided, which is supported at the rear end of the ball nut 15 via a further axial bearing 28 designed as a thrust bearing. With the cage 27, the mouthpiece 23 is connected on train. If the spindle 16 is now moved into its front end position, the forces exerted by the clamping jaws 19 on the mouthpiece 23 are derived via the cage 27 and the thrust bearing 28 onto the ball screw nut 15. In this case too, the outer housing 2 does not have to absorb any forces. The forces can take on considerable sizes in particular if, due to dirt or jamming, it is difficult to release the clamping jaws 19 from the chuck housing 20.

At the rear end of the spindle 16 there is also a stop 29 which comes into contact with the ball screw nut 15 when the spindle 16 is moved into its front end position. This avoids that, by an unlimited movement of the spindle 16, forces can be exerted on the inner housing 24, which could ultimately lead to excessive stress on the cage 27 or other housing parts.

The spindle 16 has a through bore 30 in which a mandrel disposal path is arranged. For this purpose, the pressure piece 21 has a tubular extension 31. The pressure piece 21 is also provided with a through hole extending the bore of the extension, which opens into the free space between the clamping jaws 19. The mandrel of the blind rivet, which is held between the clamping jaws 19, generally projects at least partially into the pressure piece 21. After demolition, it can be guided through the extension 31 to the rear. Between the extension 31 and the bore 30 of the spindle 16, a tube 32 is telescopically displaceable into the spindle 16 at the rear end. This tube 32 is axially immovably attached to the outer housing. The mandrel disposal path is therefore of variable length. Although it ensures the safe and reliable guidance of torn off thorns in every position of the spindle 16, the overall length of the blind riveting device 1 is not increased during operation.

The pipe 32 opens into a removable collecting container 33 and projects into it by a small length. This prevents torn mandrels that are already in the collecting container 33 from getting back into the tube 32 and thus into the mandrel disposal path. Operation without the collecting container 33 is possible. The mandrels of the blind rivets fall out of the blind riveting device 1.

As can be seen in particular from FIGS. 3 and 4, two limit switches 34, 35 are arranged at the rear end of the outer housing 2, the limit switch 34 for the front limit position and the limit switch 35 is responsible for the rear end position of the spindle 16. The function of the two limit switches 34, 35 is explained in more detail in connection with the circuit arrangement shown in FIG. 5. The limit switches are designed so that they switch at or shortly before reaching the respective front or rear end position, thus preventing the spindle 16 from reaching its extreme end position. Shown are mechanical switches which are actuated by the spindle 16 or an actuating element arranged thereon, for example by mechanically pivoting a flag 36. However, switches are also possible which are not actuated by mechanical forces, for example electronically operating, contactless semiconductor switches or magnetically actuatable switching elements, for example protective gas contact switches. The limit switches 34, 35 are preferably arranged so that they are actuated before the stops 26, 29 come into contact with the ball screw nut 15. The stops 26, 29 then form a safety device downstream of the limit switches 34, 35. The limit switches 34, 35 and the torque supports 17 are not shown in FIG. 1 for reasons of clarity.

Fig. 5 shows schematically a circuit arrangement for operating the motor 5, the switch positions for the case of the front end position of the spindle 16 being shown. The positive pole of the accumulator 6 is connected on the one hand to a contact 53 of a controlled switch 38, and on the other hand to the movable contact 44 of the actuating switch 7. Furthermore, the positive pole of the accumulator 6 is connected to a contact 56 of a second controlled switch 39. The controlled switches each have a relay 40, 41, the one Movable contact 47, 48 switches between two contacts 53, 54 and 55, 56 back and forth. Of course, the controlled switches 38, 39 can also be designed in the form of semiconductor switches.

The negative pole of the accumulator 6 is connected to the respective other contacts 54, 55 of the controlled switches 38, 39. It is also connected to a contact 50 of the front limit switch 34 and to a contact 51 of the rear limit switch 35.

The movable contact 46 of the front limit switch 34 is connected to a control connection of the controlled switch 38. The other contact 49 of the front limit switch 34 is connected via a resistor 59 to the other control connection of the controlled switch 38. A delay device 42 is arranged in parallel with the controlled switch 38. This is also connected to the two control connections of the controlled switch 38. In the simplest case, the delay device 42 can be formed by a capacitor connected in parallel to the control path of the controlled switch 38. The other contact 49 of the front limit switch 34 is connected via a resistor 59 to the control terminal of the controlled switch 38 which is not connected to the movable contact 46 of the front limit switch 34.

The other controlled switch 39 is connected in a similar manner, ie its two control inputs are connected to a delay device 43. One control input is connected to the movable contact 45 of the rear limit switch 35 and the other control input is connected via a resistor 60 to a contact 52 of the rear limit switch 35.

The two control inputs of the controlled switches 38, 39 which are not connected to the movable contacts 45, 46 of the limit switches 35, 34 are connected to contacts 57, 58 of the actuating switch 7.

The relay 40 of the one controlled switch 38 switches a movable contact 47, which is connected to the motor 5, between the contact 53 connected to the positive pole of the accumulator 6 and the contact 54 connected to the negative pole of the accumulator 6. The relay 41 switches the movable contact 48, which is also connected to the motor 5, between the contact 56 connected to the positive pole of the accumulator 6 and the contact 55 connected to the negative pole of the accumulator 6.

The entire circuit can also be implemented with other, for example electronic, components with the same function or effect.

The arrangement works as follows. The state is shown in which the spindle 16 is in the front end position. In this end position, the mandrel of a blind rivet can be inserted into the blind riveting device 1. After the blind rivet has been brought to the desired location, the actuating element 37 of the actuating switch 7 is actuated. Here, the movable contact 44 is released from the contact 58 and connected to the contact 57. There is now a control current path from the positive pole of the accumulator 6 via the movable contact 7, the fixed contact 57, the relay 41 of the controlled switch 39 and the rear limit switch 35 to the negative pole of the accumulator 6. The relay 41 picks up immediately and releases the movable contact 48 from contact 55 and brings it to contact 56 to the system. This turns a circuit from the positive pole of the accumulator 6 via the motor 5 to the negative Pole of the accumulator 6 is formed. The motor 5 now rotates, the spindle 16 being moved in the direction of its rear end position via the gear device formed by the pinion and the ball screw drive. After the spindle 16 has traveled a certain distance, depending on the properties of the blind rivet and its mandrel, the mandrel departs. Since the spindle is no longer in its front end position, the front end position switch 34 is switched over, ie the movable contact 46 is now in contact with the contact 50.

The operator can now let go of the actuating element 37 of the actuating switch 7. The movable contact 44 thereby comes into contact with the contact 58. There is now a control current path for the controlled switch 38, ie the relay 40 is supplied directly with a control current and moves the movable contact 47 so that it is in contact with the Contact 53 is coming. The control current path to relay 41 is interrupted. The relay 43 prevents the relay from falling off. This results in a short circuit path for the motor 5 via the movable contact 47, the contacts 53 and 56 and the movable contact 48. The delay time of the delay device 43 is dimensioned such that it is approximately as long as the braking time of the unloaded, idling motor 5. Thus, when the motor 5 has come to a standstill, the relay 41 moves the movable contact 48 again into the position shown in FIG. 5, ie for contact with the contact 55. A current circuit now results for the motor reverse direction, ie from the positive pole of the accumulator 6 via the contact 53, the movable contact 47, the movable contact 48 and the stationary contact 55 to the negative pole of the accumulator 6. When the actuating element 37 of the actuating switch 7 is released, the motor is first short-circuited and then automatically reversed, so that the spindle 16 is again moved into its front end position. When the spindle 16 actuates the front limit switch 34, the movable contact 46 is brought back into contact with the contact 49. The capacitor 42 is suddenly short-circuited via the resistor 59. The relay 40 then drops off immediately and restores the short-circuit circuit shown in FIG. 5 for the motor via the contacts 54 and 55. The motor can then brake very quickly, as a result of which the spindle 16 comes to a standstill in its front end position.

If, for whatever reason, the operator does not let go of the actuating element 37 of the actuating switch 7 before the spindle 16 has reached the rear limit switch 35, the spindle 16 will actuate the rear limit switch 35, that is to say the movable contact 45 for contacting the contact Bring 52. By actuating the rear limit switch 35, the capacitor 43 is short-circuited. The relay 41 of the controlled switch 39 drops out and establishes the short-circuit path shown in FIG. 5 for the motor 5. The motor 5 is then braked immediately in the rear end position of the spindle 16. When the operator then releases the actuator 37, the relay 40 is supplied with control current via the front limit switch 34 and the actuation switch 7, whereby the motor 5 is supplied with current via the contact 53 and the contact 55. He then reverses and moves the spindle 16 back towards the front end position.

The delay device 42 assigned to the controlled switch 38 is provided in the event that the operator presses the actuating element 37 of the actuating switch 7 at a time when the spindle 16 is still being moved into its front end position. The delay devices 42, 43 cause the motor 5 to be short-circuited briefly before it receives a current in the opposite direction. This avoids sudden loads on the engine and related parts.

As can be seen from FIG. 5, both the actuation switch 7 and the limit switches 34 and 35 are only acted upon by control currents, which can have a relatively low strength. These switches can therefore be dimensioned relatively weak.

To protect the motor, an overload safety device 61 can also be provided, which interrupts the current flow to the motor, for example, when the current has an amplitude over a predetermined period of time that exceeds a predetermined dimension.

With the circuit arrangement shown, the operator can avoid all unnecessary movements of the motor 5 without great effort. Since the operator releases the actuating element 37 anyway after the blind rivet mandrel has been torn off, the motor 5 can be reversed immediately and the spindle 16 can be returned to its starting position. Since the motor 5 only has to apply the torque that is necessary to tear off the mandrel of the blind rivet, that is, it does not have to charge any energy store during the movement to tear off the mandrel, it can be smaller and with a lower power consumption be dimensioned. On the one hand, this is advantageous because it allows the weight of the blind riveting device 1 to be kept small, which increases the convenience of work considerably. On the other hand, the blind riveting device 1 is particularly suitable for use in connection with a rechargeable battery 6 or a battery, that is to say there are no annoying energy supply lines. This frees up the operator to work. On the other hand, a larger amount of blind rivets can be set with a given amount of charge of an accumulator because of the low power consumption.

Claims (17)

1. Blind-rivet tool with a housing and a pulling means (4) which comprises a gripping mechanism (3) and can be moved by an electric motor (5) via a gear train (9-16) with a gear ratio independent of the position of the pulling means (4) and comprising a ball screw drive with a nut (15) and a spindle (16), characterised in that the electric motor (5) and the pulling means (4) are permanently connected to one another via the gear train (9-16) so that there is a permanent operative connection between the electric motor (5) and the pulling means (4) and the movement of the pulling means (4) is controlled exclusively by the electric motor (5).
2. Blind-rivet tool according to claim 1, characterised in that the nut (15) is driven and the spindle (16) is connected to the pulling means.
3. Blind-rivet tool according to claim 2, characterised in that the nut (15) has external toothing (14).
4. Blind-rivet tool according to one of claims 2 to 3, characterized in that the spindle (16) is hollow and forms a mandrel removal path communicating with the gripping mechanism (3).
5. Blind-rivet tool according to claim 4, characterized in that a tube (32) projecting telescopically into the end of the spindle (16) remote from the gripping mechanism (3) is arranged in the housing (2), the spindle (16) being axially movable relative to the tube (32).
6. Blind-rivet tool according to one of claims 2 to 5, characterised in that the housing has a nose piece (23) supported via a thrust bearing (25) on the nut (15).
7. Blind-rivet tool according to claim 6, characterised in that the nose piece (23) is connected to a cage (27) at least partially embracing the nut (15) and being supported via a second thrust bearing (28) on the side of the nut (15) remote from the nose piece (23).
8. Blind-rivet tool according to one of claims 2 to 7, characterised in that a stop (26, 29) for at least one direction of movement is arranged on the spindle (16) and comes to bear against the nut (15) after a predetermined axial movement of the spindle (16).
9. Blind-rivet tool according to one of claims 1 to 8, characterised in that an electric circuit arrangement (Fig. 5) is arranged upstream of the electric motor (5) and drives the electric motor (5) in one direction when the actuating switch (7) is actuated and in the other direction when actuation is completed.
10. Blind-rivet tool according to claim 9, characterised in that the circuit arrangement short-circuits the electric motor (5) for a short time when actuation of the actuating switch (7) is completed.
11. Blind-rivet tool according to claim 9 or claim 10, characterised in that the circuit arrangement has at least one controlled switch (38, 39), the control signal of which can be controlled by the actuating switch (7).
12. Blind-rivet tool according to claim 11, characterised in that a delay means (42, 43) is associated with the controlled switch (38, 39) and delays the actuation of this switch by a predetermined time interval.
13. Blind-rivet tool according to claim 12, characterised in that the time interval is the same length as the stopping time of the unloaded short-circuited electric motor (5).
14. Blind-rivet tool according to one of claims 11 to 13, characterised in that two controlled switches (38, 39) in the form of two-way switches are provided and together switch two different short circuits.
15. Blind-rivet tool according to one of claims 9 to 14, characterised in that at least one limit switch (34, 35) is provided which can be actuated by the spindle (16) and interrupts the power supply to the electric motor (5).
16. Blind-rivet tool according to claim 15, characterised in that the limit switch (34, 35) puts the associated delay means (42, 43) out of action when it is actuated.
17. Blind-rivet tool according to claim 15 or claim 16, characterised in that the limit switch (34, 35) switches the control signal.

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