FASTENING APPARATUS AND THE APPARATUS COMPRISING THE DEVICE

The invention concerns a device for a gas-powered fastening device for fastening elements, which comprises a gas cartridge connected to a combustion chamber through the intermediary of a transmission device consisting of an electromagnetically controlled valve.

As gas-powered fastening apparatuses, we can consider, for example, nail guns, hammers and other stapling devices.

The valve, in reference to Figure 1, is controlled by a control module I that is powered by a batteiy 11 and which supplies a solenoid 6 with current through V an output stage 8, which is generally a power transistor 8.

Solenoid 6, when it is powered, causes opening of the valve and allows admission of gas into the apparatus' combustion chamber starting from the gas cartridge 3 through an admission nozzle 4.

Mien the quantity of gas judged necessary is admitted into the chamber, module 1 stops the current power supply from solenoid 6 which discharges into protection diode 7 for the outlet stage and which allows closure of valve 2 through the action of a return spring (not shown).

In reality, it can be shown that the precision of the quantity of gas admitted into the combustion chamber has not, up to now, been a specific focus. Now, it is the cause of operating inconsistencies that could result in premature wear of the device,, or at least a reduced efficiency.

The applicant had the idea to seek a means of precisely adjusting this quantity of gas. In this way, the invention involves a control device for a gas transmission valve for a gas cartridge in a combustion chamber in a gas-powered fastening device, comprising a valve control solenoid, and distinguished by the fact that it comprises an adjustment circuit to stabilize the discharge of said solenoid.

Preferably, the device comprises, at its output, a discharge diode for the solenoid for evacuating the electrical energy stored therein while the valve is being opened, where the adjustment comprises at least one voltage adjustment diode that is mounted in series with the discharge diode.

In this case, the voltage adjustment diode can be a Zener diode, selected as a function of its breakdown voltage or Zener voltage in order to adjust the closure speed of the valve to a desirable value.

The invention likewise concerns a gas-powered fastening device that comprises the control device of the invention.

The invention will be better understood in the light of the following description of a preferred manner of embodiment of the solenoid motor for the gas-powered fastening device according to the invention, and of the drawing illustrating it, in which:

- Figure 1 is a sketch of the ordinary control device for a gas admission valve for a gas-powered fastening device;

- Figure 2 is a timing chart for multiple electrical controls for a valve including the one resulting from the control device in compliance with the invention;

- Figure 3 is the path of a characteristic current-voltage for a discharge circuit;

- Figure 4 is a sketch of the control device for a valve in a gas-powered fastening device in compliance with the invention;

- Figure 5 is the path of characteristic current-voltages of discharge and adjustment circuits in compliance with the invention;

- Figure 6 is a timing chart of the progress of the control current and voltage at the solenoid ends without the adjustment circuit in the invention and - Figure 7 is a timing chart of the progress of the control current and the voltage at the control device ends in compliance with the invention.

In reference to Figure 2, the instants are counted starting from the instant referenced 0 at the start of the control applied by module 1, and further to the power supply of solenoid 6 in a current Ic delivered by this same module 1, tl is the instant that valve 2 opens and t2 is the one when this power supply is stopped.

Instant tl is constant because the increase in current I so that it reaches opening threshold Io in valve-opening solenoid 6 is short in duration.

In order to close valve 2, starting from the time t2 when power supply to solenoid 6 is stopped, diode 7 more or less rapidly evacuates the energy stored in solenoid 6, according to one of the closure curves, 13 or 14, and the instant that valve 2 is closed occurs only when I reaches a residual current If within which the magnetic action of solenoid 6 can no longer compensate for the action of the return spring in valve 2, i.e. after a variable period, closure can take place between instants t3 and t4 which correspond to characteristic discharge curves 13 and 14 of solenoid 6 in diode 7.

By using voltage-adjusting diode Zener 9, in series with discharge diode 7 (Figure 4), we can achieve closure of valve 2 within a discharge time interval t5-t2 corresponding to curve 15 with a greater slope and which is much better stabilized because it is much shorter, allowing us to obtain a time period T for opening valve 2 that is equal to t5 - tl, which is much more stable, and therefore predictable, which allows it to be controlled. We shall note here that diode Zener 9 is in the passing direction opposite that of discharge diode 7.

Consequently, the quantity of gas admitted into the combustion chamber is much more precise. In reference to Figure 3, the characteristics 21 and 22, representing current Id circulating in the discharge circuit 7, and which therefore here a discharge diode, as a function of the voltage V at the ends of solenoid 6, presents an elbow to the voltage of threshold Vo of approximately 0.6 volts starting from which diode 7 passes. All diodes known as adjustment diodes have a threshold diode of approximately this value.

The discharge diode 7 allows evacuation of the energy stored in solenoid 6 through a current Id that is established at a value that is equal to Vo/L, where L is the reactance of solenoid 6.

The characteristic current voltage curves, dashed lines 21-22 for discharge diode 7, dashed lines 33-31-32 for diode Zener 9, which are opposite those in discharge diode 7, and a solid line 34-35-36 for the characteristic of both the two diodes are shown in Figure 5.

In the most frequently used direction, the two diodes have the same characteristic and have a threshold Vo of 0.6 volts and here -Vo for the Zener 9 diode, because it is in opposition to the discharge diode 7.

Because the two diodes 7 and 9 are in series, in the blocked direction of discharge diode 7, no current Id can circulate in the Zener 9 diode, which allows module 1 to control the opening of valve 2 under the same conditions as if the Zener 9 diode was not present.

On the other hand, in the blocked direction of a Zener diode, i.e. here, and for the same reason as above, in the usual direction of discharge diode 7, the characteristic of the Zener 9 diode presents an elbow to the Zener voltage Vz, or breakdown voltage, of about 6.8 volts.

Since the two diodes are in series, it is this zener voltage that determines the voltage at the ends of solenoid 6 and therefore the value of current Id of its discharge at the moment valve 2 is closed, which here is basically equal to (Vo + Vz) / L. The stiffness of the characteristic curve 15 is thus at least ten times greater and the imprecision at instant t5 when valve 2 closes will change in the same proportion, at least ten times less. The result is that the quantity of gas admitted into the combustion chamber is more precisely determined.

The functional difference between the control devices before and after installation of the zener 9 diode is well illustrated in Figures 6 and 7.

In Figure 6, timing chart 40 of voltage V at the ends of solenoid 6 is in solid lines and chart 45 of currents Ic and Id in dotted lines. The cross-hatched surface 41 corresponds to the image of the energy evacuated by diode 7. It is spread out over time just as the time period T is terminated at an instant t3 or t4 later relative to the instant t2 when valve closure control 2 is activated.

On the other hand, in Figure 7, the crosshatched area 43 that corresponds to the image of the energy evacuated by diode 7 is spread out in voltage just as the time period T terminates at an instant t5 that is very close to instant t2 when valve closure control 2 is activated.

We can choose the Zener diode based on its breakdown voltage or its zener voltage Vz in order to further increase the brevity of the time period t5 - t2 and thus adjust the precision and the speed of closure of valve 2 to the desired value. Vz can be selected from between about 6.8 and 20 volts. In effect, the maximum value of the current Id is equal to the current between tl and t2 (Id max = Vbattey / Rsolenoid). The maximum value of current Id does not depend on the Zener voltage. From the value of the voltage to the Zener voltage depends on the slope of the discharge current but not the maximum value of the current. If the Zener voltage selected is greater than 6.8 V, the closure time between t2 and t5 hardly decreases any more at all, because the speed of valve 2's closure is limited by the speed of the shift in the return spring (mechanical limit). Instead of the Zener diode, we could have added n adjustment diodes Di (not shown) in series with the discharge diode 7, where current I has the value (n + 1) Vo / L which is much greater than the one above, and the energy is evacuated much more quickly and is likewise made more stable. But there would then have had to be many more diodes in order to obtain a speed of closure for valve 2 that would lead to proper stability of T. This solution is one of less interest.