Device for detecting positioning of a staple for a frame assembling machine, and method for using said device

A spring (18) is interposed between the sliding carriage (6) carrying a hammer (13) for driving-in and the actuator rod. The spring is mounted on the head (15) of a push rod, which carries a push contact (16) surrounded by an insulating washer (17). A O pad (20) is housed in the central opening of another insulating washer (19) supported by the spring. These detection means are activated when the spring is compressed in response to the stapling effort required at the moment when a staple comes up against the frame mouldings to be assembled. Application in frame-assembling machines.

The invention is situated in the technical field of frame-assembling machines and relates more specifically to a device for detecting engagement of a staple against the mouldings being stapled, and to a method of using it.

Frame-assembly machines are known to comprise a work surface, on which the workpiece is positioned, and a movable mechanism which is arranged mainly beneath the said work surface and which serves to cause a hammer to act in an upwards direction. The hammer passes through a stapling bar holding the frame or moulding, and the movement of the hammer is subject to a contrary movement of a press projecting above the work surface, the function of which is to hold the frame in place and to act as an abutment for the hammer. The staples, provided from a bar of staples or magazine, are brought to the level of the table in a dispensing head located perpendicular to the hammer.

In known machines of that kind there is no reliable and efficient system which provides certainty that a staple has been correctly inserted at the location in question. For that it would be necessary to be certain of the number of staples contained in a magazine so that they could be counted out precisely and, as a result, to be certain that they had been correctly applied. However, that number is known only to within a few staples. It would also be possible to measure the length of the bars of staples in order to ascertain their number, but for that a precise measuring device, which would be awkward to use, would be needed.

These difficulties have led the Applicant to devise and implement a device allowing the engagement of a staple against the mouldings being stapled to be detected automatically, which device is no longer based on verification of the presence of the applied staple or absence of a staple at the application site but on detection of the effort required of the drive unit of the machine in order to drive the staple into the mouldings.

Accordingly, the invention relates principally to a device for detecting the engagement of a staple, for a frame-assembling machine, comprising a stapling bar accommodating a staple-dispensing head and also a carriage sliding in a vertical direction below the said bar along guide columns, and carrying a hammer for driving in the staple, the said carriage being moved by the rod of an actuator, according to which device a spring is interposed between the sliding carriage and the rod of the actuator, and according to which device the said spring is associated with detection means and activates those means in response to the stapling effort required when a staple comes up against the frame mouldings to be assembled.

Advantageously, the spring is a spring having non-touching turns which is mounted on the head of a push rod whose bottom region is connected to the rod of the actuator. The detection means comprise, on the one hand, a push contact located on that head and surrounded by an insulating washer and, on the other hand, a pad housed in the central opening of another insulating washer supported by the spring.

The invention relates also to a method of using the device, according to which, firstly, the actuator is activated at reduced speed until the staple has come up against the mouldings of the frame at a slow speed so as not to blunt the sharp wire of the staple, and according to which, secondly, the machine accelerates the upstroke of the actuator for complete insertion of the staple.

FIG. 1shows an assembly machine comprising a work surface1, on which the mouldings rest, supported against adjustable stops2. Underneath the work surface there is fixed a stapling bar3accommodating a staple-dispensing head4flush with the top of the work surface. Also underneath the work surface there are likewise fixed guide columns5for a carriage6sliding in a vertical direction, the travel of which is limited by a bottom stop7. A push rod8, which moves through a central opening in the bottom stop, is connected, in its lower region, to the rod9of a suspended actuator10, whose vertical movement in an upwards direction or in a downwards direction is transmitted, by way of a post12, to a press11located above the work surface.

It can be seen more precisely fromFIG. 2that a hammer13is capable of passing through the dispensing head4located in the stapling bar3. The hammer, which serves to drive in the staple, is itself fixed on a hammer support14mounted on the sliding carriage6.

At the top of the push rod8is a head15carrying a push contact16surrounded by an insulating washer17. A spring18having non-touching turns, which can consequently be compressed, rests on top of that washer17and itself supports another insulating washer19provided with a central opening in which is housed a pad20. The washer is covered by an insulating disc21. The push head15and its accessories slide inside a guide sleeve22mounted underneath the sliding carriage6. In addition, a closure plate23is likewise fixed, by means of screws24, in an appropriate recess in the sliding carriage. The spring18is accordingly interposed between the sliding carriage6and the rod9of the actuator. At the bottom ofFIG. 2there can be seen fixing screws25, which pass through the bottom stop7and the columns5(which are housed in guide bushes26located in lateral openings27in the sliding carriage6) and allow the entire unit to be fixed to the stapling bar3. An electrical connection cable28is mounted on the side of the sliding carriage and is connected to the pad20.

After having positioned the mouldings to be stapled on the work surface1and having confirmed the location of the staple magazine in the dispensing head, the stapling operation may be started. The sliding carriage6is then in the position shown in greater detail inFIG. 3, in which it is resting against the bottom stop7. The push rod8accordingly projects out below the bottom stop whilst the guide columns5extend out above the sliding carriage. The hammer13, mounted on its support14, is accordingly in its lowered position at the level of the bottom of the dispensing head.

In order to be certain of the application of a staple, the actuator10is activated, at reduced speed, which has the effect of causing the rod9to move out from the actuator10. In response, the post12starts to move in a contrary, descending direction, which has the effect of bringing the press11to rest on the mouldings. On continuation of its travel, the rod9of the actuator10brings about, by way of the spring18and the push rod8, the upstroke of the sliding carriage6. The push rod has accordingly slid through the bottom stop7and lifted the sliding carriage6until the hammer13reaches a staple and pushes it against the mouldings to be assembled. The resistance offered by the mouldings to penetration by the staple is transferred, by way of the hammer13and the sliding carriage6, to the spring18interposed between the carriage and the push rod8. The spring is compressed, thereby causing the washers17and19to come together, which ensures that the pad20comes into contact with the push contact16mounted on the head15. In other words, the detection means, comprising the pad20and the contact16, are activated in response to the stapling effort required when a staple comes up against the frame mouldings to be assembled, that being done at a slow speed so as not to blunt the sharp wire of the staple. This facilitates subsequent penetration by the staple, which follows a highly rectilinear and better targeted path, without subsequent deformation. The signal received accordingly corresponds to detection of the engagement of a staple to the mouldings. On receiving that signal, the machine accelerates the upstroke of the actuator10. Complete insertion of the staple is accomplished by virtue of the continued deployment of the rod9of the actuator and the upstroke of the hammer13, whilst benefiting from the effect of squeezing exerted between the hammer and the press11. The sliding carriage6then comes to the maximum raised position shown inFIG. 4, in which the staple is fully driven into the mouldings. At that moment, the carriage6comes into contact with the sensor29, which causes the actuator to stop and the sliding carriage to return to its initial position shown inFIG. 3. The device provides security of assembly because it is difficult to see a driven-in staple with the naked eye. The machine is then ready for application of a new staple.

In the event of a staple being absent at the moment of application, because the staple magazine is empty or because there is an anomaly in the positioning of the staple in the dispensing head, the upstroke of the sliding carriage6will be carried out until it arrives at the end of its travel, which is detected by the sensor29. However, because there has been no effort of driving in the staple, the spring18will not have been compressed and an engagement signal will not have been emitted by the detector20. That absence of a signal is accordingly an immediate indication of the absence of a staple, the detection of which wilt allow the machine to recommence the application operation at the same location after it has been reloaded. By virtue of this reliable system, it is accordingly impossible that a frame will lack any staples.

The described device likewise allows the application of a second staple as an extension to driving a first staple into the wood, this being necessary for the assembly of relatively thick mouldings. When the facetted region of the second staple comes up against the flat region of the first, the spring18is compressed, as in the previous case, and the signal of engagement is emitted in normal manner. The second staple then pushes the first into the mouldings and takes its place in the slot created in the wood, which serves as a guide for it and prevents it from being driven in to the side of the first.

Operation for the application of a second staple is, accordingly, entirely identical to that of the first and, if a staple is absent, that is detected in corresponding manner.