GB2033047A - Driving device for the cam- shaft of a brush making machine - Google Patents

Abstract

The cam-shaft of a brush-making machine is driven stepwise by a worm/worm wheel transmission of which the worm (3) has portions (12) of zero helix angle. <IMAGE>

Description

SPECIFICATION Driving device for the cam-shaft of a brush making machine This invention relates to a driving device for the cam-shaft of a brush making machine and it relates more particularly to a driving device using a worm/worm wheel transmission for stepwise driving the said cam-shaft.

It is known that the cam-shaft of a brush making machine is generally provided with three cams the shape of which is accurately determined by the location of the holes or the bristle or fiber tufts within the body of a brush, it being the purpose of said cams to determine at any time the accurate position of the brush body under the boring or filling tool.

It is also known that the said cam-shaft of the very first brush making machines was provided with a ratchet wheel generally comprising teeth in a number equal to that of the holes provided in that concerned brush, said ratchet wheel rotating tooth by tooth so that the cams secured on the shaft are making angular shiftings corresponding each to a determined working point on the brush body.

The great advantage of such driving device is that the said cams may be made very simply since only the distance between each point situated on the outer periphery of the cam and corresponding to a rest position thereof under the cam follower or a similar element being driven, and the center of the cam or the shaft on which it is secured, must be very accurate, whereas no particular requirement is laid upon the transition portions between the said points. In addition, said cams have small sizes.

However, the major drawback of such driving devices is that the speed of-the so driven brush making machine is very limited, In fact, as it is generally known, with such driving device, the accurate rest position of said ratchet wheel or the said cam-shaft cannot be controlled from a determined speed so that the brush bodies are not worked at the required location.

In order to prevent such drawback, in other words in order to substantially increase the speed of said brush making machine, the said pawl and ratchet wheel driving device has been replaced by a worm/worm wheel driving device, i.e. a continuous driving device. However, in spite of the fact that it is now possible to advantageously work more rapidly, it has been found a substantial drawback not only in that the cams are more intricate, but also in that they have also substantially larger sizes and are consequently heavier so that, on one hand, such cams are very expensive and, on the other hand, owing to the high weight thereof, they are replaced with difficulty, said replacement being necessary when other brush bodies must be worked.

In fact, with such cams, it must be taken into consideration that the time necessary for boring a hole and/or introduce a fiber tuft within the body of a brush results from a circular portion of the cam, whereas the transition portions between two of said circular portions must be made accurately according to a favourable kinetic law, still with the view of reaching high speeds, e.g. by giving a sinusoidal shape to said transition portions, in other words in order to obtain a uniform acceleration up to the center of the transition portion or uniform deceleration down to the following circular portion.

According to the present invention, the above step by step driving device is obtained by giving a very particular shape to the worm/worm wheel transmission in order to obtain, on one hand, the advantages of the above mentioned pawl and ratchet wheel driving device and, on the other hand, the advantages of the above mentioned continuous worm/worm wheel driving device, while totally excluding the drawbacks associated with both driving systems.

Thus, by using the above driving device, the following advantages are obtained: -possibility of driving the brush making machine at a very high speed; continuous connection between the driving part and the driven part, thereby providing permanently an accurate localization; -cams having small sizes; simple cams wherein it is only necessary to accurately determine the points which, at rest, must be located under the machine part being driven, whereas the transition portions situated between two of said rest positions, have no substantial importance.

For this purpose, the driving device having the foregoing and other advantages comprises a device driving the cam shaft of a brush making machine wherein said drive is obtained by using a worm/worm wheel transmission, characterized by using a worm known per se one single helical turn of which has a purely radial portion.

The characteristics of this invention will be more readily understood by the following description of a preferred embodiment given without any limitation, reference being made to the enclosed drawings in which: Figure 1 is a diagrammatic front view of a cam-shaft driving device as conventionally used heretobefore in the brush making machines; Figure 2 is a view similar to Fig. 1, but showing a driving device according to the invention; Figure 3 is a front view, on an enlarged scale, of the worm according to the invention.

Fig. 1 shows a driving device as conventionally used heretobefore for a cam-shaft 1, said driving device comprising substantially a worm wheel 2 secured on said shaft 1 and positively driven through a worm 3. In this arrangement, each cam 4 secured on said shaft is continuously rotated with the view of shifting a cam-follower 5 and more particularly a lever 6, thereby imparting to the brush body being worked and through a suitable transmission, either a length movement and/or a width movement and/or a depth movement, it being however understood that another cam 4 and another transmission 5, 6, etc. are provided for each of said movements.

As it is shown clearly in Fig. 1, said cam 4 is relatively large relative to a determined worm/worm wheel transmission, said cam being divided into short portions 7 and longer portions 8, the shortest portions being formed by circular portions, in other words, circular portions starting from the centre of the shaft 1 and the purpose of which is to stop for a while the lever 6 and the workpiece connected thereto, as well as the transition portion 8 which is situated between said two circular portions and which forms the connection therebetween, in other words, which allows to shift the brush body so that another hole may be bored or so that another fiber tuft may be introduced.

Fig. 2 shows a driving device according to the present invention through a view similar to that of Fig. 1 and on the same scale. In that case also, the cam-shaft 1 is driven through a worm wheel 2 from a worm 3 in order to actuate suitable cams 4 which, in that case, are only formed with transition portions 8 connecting points 9, said points 9 determining the rest positions under the camfollower 5, in other words, the stop times during which the body of a brush is bored or filled.

The transition portions 8 of the known driving device shown in Fig. 1 must be formed according to a favourable kinetic law, e.g. with a uniform acceleration from the point 10 up to the center of the transition portion 8 and then with a uniform deceleration down to the point 11, in other words, the end of the transition portion 8, whereas in the embodiment shown in Fig. 2, said transition portions 8 have substantially no importance, since only the points 9 are determining for correctly operating the machine.

Thus, in order to obtain cams 4 having small sizes and of a simple structure as compared with cams 4 having very large sizes and an intricate structure like those used in the driving device known heretofore and as shown in Fig. 1, a worm/worm wheel driving device as conventionally used in the known machines has been selected, but with such great difference that each pitch of the helix of the worm 3 has a portion 12 which is perpendicular to the axial line of said worm, said portion 1 2 having a length a larger than the width of the worm wheel 2, whereas the length of said portion 1 2 is determined as a function of the time necessary for carrying out the said boring or filling step in the body of the brush, so that said length which determines the rest time of the lever 6 and the means assembled thereto, corresponds to the shifting time of angle ss in the embodiment shown in Fig. 1. During said time, the worm wheel is hold at rest so that, at the point 9 which, at that time, lies under the cam-follower 3, the cam 4 is also kept at rest.

The helical portion of each pitch of the helix of the worm 3 corresponds to the angle a, in other words to the time during which the cam is shifted to bring the brush body being worked from a working position to another.

Preferably, a sinusoidal shape will be give to the transition portions between the above straigth portions 1 2 of each pitch of the helix of the worm 3 and the helical portion of each pitch, thereby allowing to brake with a uniform deceleration when the straight portions 1 2 of the worm are contacting the worm wheel 2 whereas, when the straight portions 1 2 of the worm are leaving the wheel 2, a uniform acceleration is imparted thereto.

In is apparent that a very simple driving device is thereby obtained allowing to use small, simple and cheap cams which may be very readily replaced when working other brush bodies, while also allowing to operate the machine at a very high speed.

Claims (4)

1. A driving device for the cam-shaft of a brush making machine wherein a worm/ worm wheel transmission is used for such drive, charaterized by using a worm known per se one single helical turn of which has a purely radial portion.

2. A driving device according to claim 1, characterized in that said radial portion of each single helical turn has a length larger than the width of the concerned worm wheel.

3. A driving device according to any one of claims 1 and 2, characterized in that the transition portion between said purely radial portion and the helical portion of each single turn has a sinusoidal shape.

4. Driving device for the cam shaft of a brush making machine, substantially as hereinbefore described with reference to the accompanying drawings.