GB2442580A

GB2442580A - Tacker with switch-off means

Info

Publication number: GB2442580A
Application number: GB0719145A
Authority: GB
Inventors: Steffen Wuensch; Joao Jorge Bergner; Erol Ergin
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-10-02
Filing date: 2007-10-01
Publication date: 2008-04-09
Anticipated expiration: 2027-10-01
Also published as: DE102006046842A1; CN101157213A; GB0719145D0; CN101157213B; GB2442580B

Abstract

A tacker for driving fasteners 40 into a workpiece 42, comprises a housing 12 on which a handle 14 is constructed, a region 26 for holding the fasteners, and a mechanism 44 for ejecting the fasteners. A switching-off means 50a is provided, which leads to deactivation of the ejecting mechanism when the quantity of fasteners present in the holding region falls below a minimum quantity. The switching-off means may comprise at least one first light barrier (92, fig 6), which detects the presence of fasteners. Alternatively, the switching-off means may include an electrical contact (50, fig 3a) which can be closed via a magazine slide 34.

Description

Tacker for driving in fasteners

Prior art

The starting point of the invention is a tacker for driving in fasteners, in accordance with the pre-characterising clauses of the independent claims.

Tackers, which are also known as "electric tackers", are used for driving fasteners into workpieces for the purpose of bringing about a connection. With the aid of a tacker of this kind, the fasteners, for example staples, can be driven into the particular workpiece in quick succession, said fasteners being conveyed to the staple shaft from a magazine which is present in the appliance. Use is made, for example, of staples of differing leg length, back breadth and wire thickness, with corresponding tensile strength of the wire used. The staples are not introduced into the staple shaft of the tacker individually, but in magazined form. A tacker of this kind is described, for example, in EP 0 510 351 Bi.

When working with a tacker, the situation can arise in which the magazine is used up during a working operation.

On account of the large number of fasteners located in the magazine, it is difficult to foresee when the last fastener will be used up. Under these circumstances, there is a risk of the tacker performing an empty stroke in which the blow which is intended to drive in the fastener does not impinge upon the fastener but upon the workpiece, resulting in damage caused by the penetration of a striker blade.

Advantages of the invention The starting point of the invention is a tacker for driving fasteners into a workpiece, said tacker having a housing on which a handle is constructed and in which a region for holding the fasteners is provided, and also having a mechanism for ejecting the latter.

It is proposed that a switching-off means be provided, which leads to deactivation of the ejecting mechanism when the quantity of fasteners present in the holding region falls below a minimum quantity. In this case, the number of fasteners that constitute said minimum quantity can be preset within the switching-off means and/or, in a particularly advantageous manner, set by a person operating the tacker. Said switching-off means may comprise an optical unit, for instance a light barrier, which can be triggered when the quantity of fasteners falls below a minimum quantity and when, as a result of a signal from the optical unit, the ejecting mechanism is switched so as to be non-functional, in particular is switched off. In addition, the switching-off means may comprise an electrical contact which is preferably closed when the quantity of fasteners falls below a minimum quantity and when, as a result of a signal from the electrical contact, the ejecting mechanism is switched so as to be non-functional, in particular is switched off. Pointless activation of the ejecting mechanism can thereby be reliably avoided.

Furthermore, provision may be made, in both variants, for the possibility of triggering a preliminary alarm when the number of available fasteners is approaching the minimum quantity. A combination of the two variants of optical and electrical switching-off means is also conceivably possible. Thus, for example, it is possible to trigger a light barrier when a defined, small supply of fasteners is still available, and to trigger an electrical contact, which then leads to deactivation of the ejecting mechanism, when the last fastener is used up. The reverse variant is also conceivably possible, in which, for example, an electrical contact can be triggered when a defined, small supply of fasteners is still available. A light barrier may be triggered when the last fastener is used up, and this then leads to deactivation of the ejecting mechanism.

No additional construction space, or scarcely any, is needed, so that the single switching-off means or plurality of switching-off means can easily be integrated into tackers.

In addition to the detection, in good time, of the using-up of fasteners, and to the prevention of empty strokes, an indication of reserve may be provided which indicates the number of fasteners, for instance staples, pins or nails, still located in the magazine of the tacker, in order to permit refilling in good time. This is helpful to a user if work with the tacker is being carried out in places which are difficult of access or on ladders, for example when attaching tongue-and-groove boards.

The switching-off means may comprise, in a preferred first configuration, at least one first light barrier which detects the presence of fasteners in the region for holding the latter. Said light barrier is advantageously positioned at a precisely defined point in the holding region, particularly in the staple shaft, without being connected directly to the latter. The presence of fasteners is optically scanned with the aid of a light beam. If no fasteners are detected, a signal can be triggered which can be processed further with the aid of an electronic system. Use may preferably be made of various photoelectric components. One-way light barriers, in which the transmitter and receiver are disposed in their own housings on either side of the stretch to be scanned and at the height of the apertures, are favourable. The one-way light barrier is used in the passive mode of operation, that is to say with the direct light path interrupted.

Thus, when the magazine is still sufficiently full of fasteners, this condition is recorded at the receiver diode, and when light passes through, that is to say fasteners are not present, a switching-off pulse is generated via an associated electronic system. Reflection-type light barriers are also suitable. These operate on the principle of the reflected light beam. The transmitter and receiver are accommodated in a common housing. In this case, the fastener or a reflector disposed on the opposite side of the magazine may cause the reflection. Reflection-type light-scanners are also suitable. In these, the transmitter and receiver are accommodated in a common housing, but it is not the interruption of the light beam, but its reflection on an object, which is evaluated. The fastener is detected when it reflects back sufficient light to the receiver. Since a switching interval between the transmitter and the fastener is small in this case, an aperture for the passage of light that lies opposite the first aperture in the magazine may advantageously be dispensed with. A fibre-optic light barrier, which can be used like a reflection-type light-scanner, is also suitable. The particular advantage of this is that the entry and exit apertures for the light can be made very small, for example with a diameter of less than 1 mm, and may be in the region of, for example, the width of the staple.

The first light barrier may preferably be interrupted when fasteners are present, and be closed when no fasteners are present. "Interrupted" means that the receiver receives no signal from the transmitter, and "closed" means that the receiver receives the signal from the transmitter, when said receiver should not receive any signal if fasteners are present. If the fastener forms part of the light barrier, for instance as a reflector, the interrupted/closed correlation is reversed. The light barrier is interrupted when no fastener is present, and closed when fasteners are present. This is the result of the type of light barrier actually chosen by the person skilled in the art. A corresponding switching-off pulse can be transmitted to the ejecting mechanism.

The tacker advantageously comprises a unit for pushing the fasteners, which is provided for the purpose of interrupting or unbiocking the first light barrier. For this purpose, an aperture, which is masked by the fasteners when the latter are present, may be provided in the pushing unit. A light beam belonging to the light barrier is sent by a transmitter, for example to a receiver, said light beam passing through the diametrically opposed apertures in the pushing unit. In this case, apertures in the pushing unit and apertures in corresponding parts of the magazine are in alignment. If fasteners are present, the light beam is interrupted. If no fasteners are present in the region of the apertures, the light beam is able to pass through and the light barrier is closed. The position of the aperture is preferably chosen in such a way that at least the penultimate fastener can be scanned by means of the focused light beam. Since the fastener always comes to rest at the same point in its magazine shaft belonging to the holding region, it is possible, if staples having the same wire thickness are used, for the switching-off pulse to be also connected to an electronic counting apparatus.

This means that, even in the case of a defined remaining minimum quantity of fasteners, a message can appear on a suitable event-indicator and warn of the using-up of the fasteners. Said event-indicator may be, for example, a indicator on the housing, by means of which text can be emitted, or a luminous strip with a length that decreases in proportion to the quantity of fasteners, an acoustic signal or the like. If the magazine is taken out for filling purposes, the light barrier or its receiver diode may additionally record this condition in the form of a switching-off pulse for the readiness of the tacker for use.

In addition, it is proposed that the tacker comprise an end stop for the pushing unit, which end stop is disposed at a distance from the first light barrier which is reached when the quantity of fasteners falls below a minimum quantity.

The first minimum quantity is preferably one, corresponding to the last fastener in the magazine. If this is used up, this condition is detected and the ejecting mechanism deactivated.

There may be provided, at a distance from the first light barrier, a second light barrier by means of which it is possible to detect that a second minimum quantity of fasteners, which is larger than the first minimum quantity, has been reached. Said second minimum quantity may, for example, be ten, so that ten fasteners are still present when a first alarm is triggered by the second light barrier. The distance between the light barriers is preferably chosen in such a way that an appropriate residual quantity of fasteners can be detected. If two light barriers are provided, apertures may be disposed in the holding region, preferably in the magazine, in a manner corresponding to the height of each light barrier. It is optionally possible, depending upon the nature of the light barrier chosen, to provide diametrically opposed apertures if the light barriers penetrate the magazine with their light beam. In the case of the reflection-type arrangements touched upon above, one aperture on the same side as the transmitter/receiver arrangement may be sufficient. The apertures in the pushing unit may be simple bores or else be constructed as a slot, at the ends of which the two transmitters or receivers may be disposed in each case. As soon as the second, rear light barrier signals that the first minimum quantity of fasteners, for example ten staples, has been reached, the second light barrier remains closed as long as the slot in the pushing unit travels forwards to the first light barrier as the remaining fasteners continue to be used up. As soon as said slot reaches the first light barrier, the latter is closed and signals the switching-off pulse. In this embodiment, the information to the effect that only a small quantity of fasteners is still present in the holding region is preserved, even if the current is interrupted, since the second light barrier is closed, as before, when switching-on occurs again.

It is possible, in favourable manner, to provide an event-indicator which triggers an alarm when the second light barrier is closed. It is thus advantageously possible to issue a preliminary warning to the user.

In addition, a counting mechanism may record a further consumption of fasteners when the second light barrier is closed, so that a person operating the tacker may be advantageously informed, by means of the counting mechanism, about the filling level and/or the consumption of the fasteners.

A second preferred configuration makes provision for a tacker for driving fasteners into a workpiece, said tacker having a housing on which a handle is constructed and in which a region for holding the fasteners is provided, and also having a mechanism for ejecting said fasteners. The tacking unit advantageously has a switching-off means which is constituted by an electrical contact that can be closed via a magazine slide. It is possible, by detecting the using-up of the fasteners in good time, to prevent an empty stroke and thereby damage to the workpiece or to the surface of said workpiece.

A spring which drives the magazine slide and has an electrically insulated front suspension and an electrically insulated rear suspension may advantageously be provided in the holding region. As a result of this, it is possible to avoid electrical contact when fasteners are present, and to achieve the desired contact-making only when a magazine is empty. This can be achieved in a particularly advantageous manner if the magazine slide is electrically insulated in relation to the spring when a minimum quantity of fasteners is present in the holding region. In this connection, a "front and rear suspension" should be understood to mean a suspension for the spring in which the front suspension is disposed on a side of the spring that faces towards the staple output, and the rear suspension is disposed on a side of the spring that faces away from said staple output.

It is further proposed that the tacker have a contact finger which is mounted upstream of the magazine slide and which closes the electrical contact when the quantity of fasteners falls below a predetermined minimum quantity.

Said contact finger brings about an electrically conductive connection via the pushing unit and the spring.

Alternatively, the contact finger and a region of the holding region may constitute the electrical contact. This is preferably a lower part of the magazine, in which a suitable contact face comes into engagement with the contact finger.

Said contact finger may advantageously be adjustable in its length. There is a close connection between the using-up of the fasteners and the contact of the pushing unit, in particular a magazine slide, with an end stop in the holding region or in the magazine. Tolerances in the tacker can be compensated for in a simple manner as a result of the possibility of adjustment. Under these circumstances, adjustment of the contact finger can take place in a partly automatic manner and/or be effected by a person operating the tacker.

Electrical connecting means, which are connected electrically when an electrical contact is closed, may also be provided in the holding region. The current supply for this electrical switching-off means may preferably be a small voltage of a few volts, which is non-dangerous to the user. The signal may be fed to an event-indicator. If there are no fasteners in the magazine or in the holding region, it is possible, for example, for an LED (light-emitting diode) to flash or for an acoustic signal, for instance a buzzing sound or a speech output, to take place.

Drawings Other advantages will emerge from the following description of *the drawings. In the latter, two exemplified embodiments of the invention are represented. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and unite them to form appropriate further combinations.

In said drawings: fig. 1 shows, in side view, a tacker in a first preferred configuration, partially cut away in its holding region; fig. 2 shows the preferred tacker from figure 1, in a plan view of a section Il-lI; figs. 3a, b show, in plan view, a detail from figure 2 with a front spring suspension with the electrical contact closed (figure 3a), and a rear spring suspension (figure 3b); figs. 4a, b show, in side view, a detailed view from figure 1 in the region of a front spring suspension (figure 4a) and a rear spring suspension (figure 4b); fig. 5 shows, in side view, a tacker in a second preferred configuration, partially cut away in its holding region;

V

fig. 6 shows a section along the line VI-VI in figure 5; fig. 7 shows a detail of the sectional view in figure 6, with a closed light barrier; figs. Oa, b show a plan view of a section Vill-VIlI through a holding region in figure 5, in which a rear, second light barrier is closed (figure 8a), and in which a front, first light barrier is closed (figure 8b); and figs. 9a, b show a detailed view from figure 8 with a rear, second light barrier with the fasteners almost used up (figure 9a), and a front, first light barrier (figure 9b) with the fasteners completely used up.

Description of the exemplified embodiments

In the figures, elements of the same type are provided with the same reference numerals.

A side view of a tacker 10 is represented in figure 1 in a first preferred configuration. Said tacker 10 exhibits a housing 12 which is partially cut away in the region of an underside 24.

The tacker 10 is placed on a workpiece 42 into which there has been driven a fastener 40 which is constructed, for example, as a staple and which has been ejected from said tacker 10 through an ejecting channel 46 by means of an ejecting mechanism 44 (inside the housing 12, figure 6)

I

Said ejecting mechanism 44, which is only indicated in outline, usually has a drive with a magnetic armature and magnetic coil and also an apparatus for generating an impact. Under these circumstances, the ejecting channel 46 projects beyond the underside 24. For the purpose of activating the ejecting mechanism 44, it is possible to actuate, on a handle 14, a switch 16 which is constructed as a switching paw?. A setting knob 18 makes it possible to set the striking force.

The ejecting channel 46 is disposed at a front end 20, while a magazine 30 can be introduced, at an opposite rear end 22, into a holding region 26 for the fasteners 40.

Said fasteners 40 are preferably laid in the magazine 30 in the magazined form usual in the trade.

Details of the holding region 26 with the magazine 30 introduced can be seen in the cut-away lower region of the tacker 10. Represented as a subassembly in a lower part 32 of the magazine are all the individual parts of said magazine 30, which is constructed as a staple magazine, such as a deflecting roller 72 with its spindle 74 as the front spring suspension 76, a spring 70 which is constructed as a draw spring and which brings the fasteners 40, via a magazine slide 34, into abutment, in each case, against a front ram-carrier belonging to the ejecting mechanism 44, and also a rear spring suspension 78. An upper magazine cover 56 masks the lower part 32 of the magazine, engaging over the sides of the latter. The fasteners 40 are brought into the upper magazine cover 56 after the magazine 30 has been taken out of the holding region 26.

Located in the rear part (end 22) of the lower part 32 of the magazine is an unlocking mechanism for carrying out refilling with fasteners 40. The unlocking mechanism is unlocked by pressing on a triggering lever 58. A return spring 60 ensures the locking of the magazine 30 after it has been pushed in.

For the purpose of deactivating the ejecting mechanism 44, an electrical switching-off means 50a is provided which leads to deactivation of said ejecting mechanism 44 when the quantity of fasteners 40 present in the holding region 26 or in the magazine 30 falls below a minimum quantity.

For the purpose of illustrating the action of the switching-off means 50a, figure 2 and figures 3a and 3b show a plan view of a section 11-Il of the preferred tacker 10 from figure 1, containing the front spring suspension 76 with the electrical contact 50 closed (figure 3a) and a rear spring suspension 78 (figure 3b), details of the front and rear spring suspensions 76, 78 being given prominence in figures 3a and 3b. Figures 4a and 4b show the corresponding regions from figures 3a and 3b respectively, in the form of detailed side views. The individual elements to which reference will be made for explanation purposes are portrayed in figure 1.

The subassemblies which are provided for making electrical contact for the purpose of deactivating the ejecting mechanism 44 when the magazine 30 is empty are the magazine slide 34 and the rear spring suspension 78.

Figures 3a and 4a show details of the magazine slide 34 in the region of the front spring suspension 76. Said magazine slide 34 comprises a staple slide formed from a sheet-metal stamping as the pushing unit 36, a contact finger 52 with the front spring suspension 76 and an electrically insulating intermediate piece 54. The pushing unit 36 is disposed between the internally located lower part 32 of the magazine and the externally located upper cover 56 of said magazine, and pushes the fasteners 40 forwards to the ejecting channel 46. The spring 70, which is constructed as a draw spring, is routed partially round the deflecting roller 72 with its axis 74 and is hooked, by means of an eye, onto a downwardly pointing peg on the intermediate piece 54. The pushing unit 36 engages, by means of a downwardly pointing end, in the peg on the intermediate piece 54.

Said intermediate piece 54 forms an electrical insulator between the draw spring 70 and the magazine slide 34 and pushing unit 36, which are metallically conductive.

When the magazine 30 has been emptied, or when a predetermined quantity of fasteners 40 in said magazine 30 falls below a minimum quantity, the contact finger 52 touches an inwardly projecting contact region 62 on the lower part 32 of the magazine, as a result of which the electrical contact 50 comes about. If, when a minimum quantity of fasteners 40 is present, the contact finger 52 is at a distance from the contact region 62, the draw spring 70 is electrically insulated from the magazine slide 34.

Figures 3b and 4b show the rear spring suspension 78, which has an electrically insulating carrier part 80 made of plastic and a metal, conductive insert 82. The spring 70 is hooked, by means of an eye, onto a peg on the carrier part 80, which peg is electrically insulated from the magazine slide 34. The insert 82 is connected to the carrier part 80 in a manner incorporated into the material thereof, and touches the electrically conductive spring 70.

Said insert 82 is constructed like a rectangular frame in which the draw spring engages. An electrical feeder cable is fastened to the insert 82.

As a result of closure of the electrical contact 50, the switching-off pulse for the ejecting mechanism 44 is triggered and prevents an empty stroke from damaging the surface of the workpiece. The electrical connection necessary for this purpose is made to the spring at the contact finger 52 of the magazine slide 34 via the electrical connection 86 and via the insert 82. Under these circumstances, the deflecting roller 72 is constructed as an electrically insulating part.

This chain of connection is uninterrupted, electrically, until the last fastener 40 is used up. After the last fastener 40 in the magazine 30, the current circuit is closed through the fact that the contact finger 52 on the magazine slide 34 makes contact electrically with the lower part 32 of the magazine. An electrical connection to a feeder cable is disposed at any desired point on said lower part 32 of the magazine. This connection and the feeder cable, which is not represented, on said electrical connection 86 (figure 4b) lead to the switching-off apparatus which is likewise not represented.

In order to compensate for exacting tolerances, the contact finger 52 is disposed so as to be longitudinally adjustable on the intermediate piece 54 by means of a screw which is not represented.

Another preferred configuration of a tacker 10 is embodied in figure 5 and represented in the form of a side view of said tacker 10, in which the housing 12 of the latter is partially cut away in the region of its underside 24.

Said tacker 10 is placed on a workpiece 42 into which there has been driven a fastener 40 which is constructed, for example, as a staple and which has been ejected from said tacker 10 through an ejecting channel 46 by means of an ejecting mechanism 44 (inside the housing 12, figure 6) Said ejecting mechanism 44, which is only indicated in outline, usually has a drive with a magnetic armature and magnetic coil and also an apparatus for generating an impact. Under these circumstances, the ejecting channel 46 projects beyond the underside 24. For the purpose of activating the ejecting mechanism 44, it is possible to actuate, on a handle 14, a switch 16 which is constituted by a switching pawl. A setting knob 18 makes it possible to set the striking force.

The ejecting channel 46 is disposed at a front end 20, while, at an opposite rear end 22, a magazine 30 can be introduced into a holding region 26 for fasteners 40. Said fasteners 40 are preferably laid in the magazine 30 in the magazined form usual in the trade.

Details of the holding region 26 with the magazine 30 introduced can be seen in the cut-away lower region of the tacker 10. Represented as a subassembly in a lower part 32 of the magazine are all the individual parts of said magazine 30, which is constructed as a staple magazine, such as a deflecting roller 72 as the front spring suspension 76 (figures 8a and 9a), a spring 70 which cannot be seen here but is constructed as a draw spring and which brings the fasteners 40, via a magazine slide 34, into abutment, in each case, against a front ram-carrier belonging to the ejecting mechanism 44, and also a rear spring suspension 78 (figures 8b and 9b) which cannot be seen here. An upper magazin cover 56 masks the lower part 32 of the magazine, engaging over the sides of the latter.

The fasteners 40 are brought into the upper magazine cover 56 after the magazine 30 has been taken out of the holding region 26.

Located in the rear part (end 22) of the lower part 32 of the magazine is an unlocking mechanism for carrying out refilling with fasteners 40. The unlocking mechanism is unlocked by pressing on a triggering lever 58. A return spring 60 ensures the locking of the magazine 30 after it has been pushed in (figures 8a and 9a).

For the purpose of deactivating the ejecting mechanism 44, an electrical switching-off means 90a is provided which leads to deactivation of said ejecting mechanism 44 when the quantity of fasteners 40 present in the holding region 26 or in the magazine 30 falls below a minimum quantity.

The switching-off means 90a (figure 5) in this example comprises a first light barrier 92 which detects the presence of fasteners 40 in the region 26 for holding said fasteners 40 and, when the quantity of fasteners 40 falls below a first minimum quantity, triggers a signal which leads to deactivation of the ejecting mechanism 44.

Provided at a distance from the first light barrier 92 is a second light barrier 98 by means of which it is possible to detect that a second minimum quantity of fasteners 40, which is larger than the first minimum quantity, has been reached. Said second minimum quantity may, for example, be ten staples, and the first minimum quantity may, for example, be one staple.

Figure 6 shows a section along the line VI-VI in figure 5 with part of the striking drive of the ejecting mechanism 44, looking towards the first light barrier 92. In figure 7, prominence is given to the region of the magazine 30.

The deflecting roller 72 with the spring 70, which is constructed as a draw spring, can be seen behind the light barrier. If there are fasteners 40 in the holding region 26, the first light barrier 92 is interrupted. If, on the other hand, the fasteners 40 in the region 26 for holding them are used up, the light barrier 92 is closed, that is to say a light beam is radiated from a diode 94 onto a reflector 96 in an unhindered mannerand is reflected back to the diode 94 again by said reflector. For this purpose there are provided, on both sides, apertures 104 which extend, in a coinciding manner, through the upper magazine cover 56, the pushing unit 36', which is constructed as a staple slide, and the lower part 32 of the magazine. The apertures 104 in the upper magazine cover 56 and the lower part 32 of the magazine are stationary, whereas an aperture 112 (figure 7) in the pushing unit 36 moves along the longitudinal axis of the appliance in dependence upon the filling level in the magazine 30. If said pushing unit 36 is displaced longitudinally in a different position as a result of fasteners 40 which are located in the holding region 26, the apertures 104, 112 are no longer in alignment, and the light barrier 92 is interrupted.

Figures 8a and 8b show a plan view of a section VIlI-Vill through figure 5. Figure Ba shows a situation in which a minimum quantity of, for example, ten fasteners 40 is still present. Figure 8b shows the situation in which the last fastener 40 is used up. Figures 9a and 9b show the corresponding positions in enlarged form.

The first light barrier 92 is disposed closer to an end stop 108 than is a second light barrier 98. Associated with the first light barrier 92 are the apertures 104, and associated with the second light barrier 98 are apertures 106 in the lower part 32 of the magazine and in the upper cover 56 of the magazine, through which the light of a diode 100 passes to a reflector 102 in the event of transmission. The aperture 112 in the pushing unit 36 is longitudinally movable with the latter.

A distance 110 between the two light barriers 92, 98 corresponds to the length of the second minimum quantity of fasteners 40, in this case, for example, ten staples.

After the consumption of the eleventh-to-last fastener 40, the magazine slide 34 or the pushing unit 36 reaches a position in which a diode 100 belonging to the second light barrier 98 emits a switching pulse to an electronic system, which is not represented, as a result of the passage of light through the apertures 106, 112 in the upper magazine cover 56, the pushing unit 36 and the lower part 32 of the magazine, which apertures are in alignment with one another. This pulse can be used for the purpose of conveying visual indications on an event-indicator 114 (figure 5) constituted by a display, and/or acoustic signals. Said event-indicator 114 is disposed at the rear end 22 of the tacker 10 in a manner which is clearly visible to a person operating said tacker 10. This "indication of reserve" invites the user to fill up the magazine 30 with fasteners 40 again.

The switching pulse generated by the light barrier 98 can also be used to activate an electronic counting mechanism 116 installed in the tacker 10 (figure 5) . When the tacker is in operation, the data from said counting mechanism 116 are conveyed, via an internal data line of which no further details are represented, to the display, where they are indicated for a person operating the tacker 10. The number of staples in the reserve, which number can be set beforehand by the user or at the factory and which corresponds to the second minimum quantity, is indicated when the diode 100 signals the passage of light through the magazine. From then on, the number of fasteners 40 still located in the magazine 30, which number can also be stored in the event of an interruption in current, appears on the display.

If the user removes a remnant of the fasteners 40 in order to put in new ones, the indication by the electronic system can be set to zero by means of a switching contact, which is not included in the embodiment, on the unlocking mechanism for the magazine 30. If the pushing unit 36 belonging to the magazine slide 34 reaches the position of the first light barrier 92 having the diode 94, the latter gives the signal, as a result of the passage of light, for deactivating or switching off the ejecting mechanism 44.

Only when the magazine 30 is filled up again with fasteners can the tacker 10 be brought into operation again.

The aperture 112 in the pushing unit 36 may be embodied as a round bore or as a slot. A slot length which is matched to the size of the second minimum quantity of fasteners 40 is advantageous. This guarantees that, as soon as the second minimum quantity, at which the second light barrier 98 responds, is reached, an event-indicator is able to emit a signal until the last fastener 40 is used up and the pushing unit 36 has arrived at the end stop 108.

The aperture 112 in the pushing unit 36 is expediently disposed at a distance from the free end so that, on reaching the end stop 108, the aperture 112 or the front end of the slot is located at the level of the first light barrier 92.

Said first light barrier 92 then also reports the passage of light, whereupon the electronic system switches off the tacker 10 or the ejecting mechanism 44.

If it is not the intention to indicate the number of fasteners 40 still remaining in a precise manner through the convenience of an electronic counting system, the variant having a slot as the aperture 112 represents a cost-effective alternative.

Claims

S Claims 1. Tacker for driving fasteners (40) into a workpiece (42),

said tacker having a housing (12) on which a handle (14) is constructed and in which a region (26) for holding the fasteners (40) is provided, and also having a mechanism (44) for ejecting said fasteners (40), characterised in that a switching-off means (SOa, 90a) is provided, which leads to deactivation of the ejecting mechanism (44) when the quantity of fasteners (40) present in the holding region (26) falls below a minimum quantity.
2. Tacker according to claim 1, characterised in that the switching-off means (90a) comprises at least one first light barrier (92) which detects the presence of fasteners (40) in the region (26) for holding said fasteners (40)
3. Tacker according to claim 2, characterised in that the first light barrier (92) is interrupted when fasteners (40) are present, and is closed when no fasteners (40) are present.
4. Tacker according to either of claims 2 or 3, characterised by a unit (36) for pushing the fasteners (40), which is provided for the purpose of interrupting or unbiocking the first light barrier (92)
5. Tacker according to claim 4, characterised by an end stop (108) for the pushing unit (36), which end stop is disposed at a distance (110) from the first light barrier (92) which is reached when the quantity of fasteners (40) falls below a minimum quantity.
6. Tacker according to one of the preceding claims, characterised in that there is provided, at a distance from a first light barrier (92), a second light barrier (98) by means of which it is possible to detect that a second minimum quantity of fasteners (40), which is larger than the first minimum quantity, has been reached.
7. Tacker according to claim 6, characterised in that an event-indicator (114) is provided, which triggers an alarm when the second light barrier (98) is closed.
8. Tacker according to one of the preceding claims, characterised in that a counting mechanism (116) is provided, which records the consumption of fasteners (40) when the light barrier (98) is closed.
9. Tacker for driving fasteners (40) into a workpiece (42), said tacker having a housing (12) on which a handle (14) is constructed and in which a region (26) for holding the fasteners (40) is provided, and also having a mechanism (44) for ejecting said fasteners (40), particularly according to one of the preceding claims, characterised by a switching-off means (SOa) which is constituted by an electrical contact (50) which can be closed via a magazine slide (34)
10. Tacker according to claim 9, characterised in that a spring (70) which drives the magazine slide (34) and has an electrically insulated front suspension (76) and an electrically insulated rear suspension (78) is provided in the holding region (26)
11. Tacker according to either of claims 9 or 10, characterised in that the spring (70) is electrically insulated in relation to the magazine slide (34) when a minimum quantity of fasteners (40) is present in the holding region (26)
12. Tacker according to one of claims 9 to 11, characterised by a contact finger (52) which is mounted upstream of the magazine slide (34) and which closes the electrical contact (50) when the quantity of fasteners (40) falls below a predetermined minimum quantity.
13. Tacker according to claim 12, characterised in that the contact finger (52) and a contact region (62) belonging to the receiving region (26) form the electrical contact (50)
14. Tacker according to either of claims 12 or 13, characterised in that the contact finger (52) is adjustable in its length.
15. Tacker according to one of the preceding claims, characterised in that electrical connecting means (86), which are connected electrically when the electrical contact (50) is closed, are provided in the holding region (26).
16. A tacker for driving fasteners into a workpiece substantially as herein described with reference to the accompanying drawings.