GB2120804A - Deflection device for laser beam in thermal surface treatments of splined pieces - Google Patents

Abstract

A deflection device (1) for deflecting a laser beam (2) for carrying out thermal surface treatments on splined elements (3) comprises two mirrors (11,12) rotating at the same speed about a respective axis (13,14), and optionally a mirror (15) stationary in an intermediate position. The mirror (11,12) are inclined at a predetermined angle to their respective shafts (13,14). The inclination of the rotary mirrors (11,12) may be adjustable relative to the respective axis, as well as the relative phase of each mirror, so that the laser beam at the outlet of the device (1), describes a squashed annular trajectory (24) substantially comparable to a straight line segment. <IMAGE>

Description

SPECIFICATION Deflection device for deflecting a laser beam in thermal surface treatments of splined pieces The present invention relates to a deflection device for deflecting a laser beam in thermal surface treatments of splined elements, i.e. elements whose zones intended to be subjected to the treatment have a substantially rectangular orsimilar configuration. By way of example, such elements may be gearwheels, splined shafts, homokinetic couplings and the like, and have working zones which require a localized increment of their wear resistance relative to the adjacent zones.

Since the zones to be subjected to the treatment generally have, as already said before, a rectangular configuration, and sincethe laserbeam generated by the source of emission has preferably a circular cross-section, deflection devices have been constructed which are capable of converting the zone of propagation ofthe laser beam from substantially circularto substantially rectangular. To this end it is known to use a rotary prism having a plurality of reflecting lateral faces. In particular, the laser beam impinges with a predetermined angle of incidence on the lateral surface of the prism which, by rotating about its own axis deviates the beam so asto make it describe a segment whose length depends on the distance between the prism and piece being treated and on the number of faces which form the lateral surface of the prism.It has been observed that the rotating prism is particularly expensive, cannot be used for high power laser beams (morethan 500W) and not suitable for carrying out treatments on zones whose amplitudes are very different from each other.

Moreover, it does not allow to treat zones of very reduced amplitude, because in such a case it should be provided with a greatnumberoffaces, and this involves considerable manufacturing difficulties.

Itis also known to use oscillating mirrors by means of which the laser beam is deflected so as to give rise to the cycling sweeping of a substantially rectangular zone. The known methods used to produce the oscillation of the said mirrors involve the use of magnetic field deflection systems, which are not able to guarantee a sufficiently stable extended use of the oscillating mirrors.

It is an object of the present invention to provide a device for deflecting a laser beam, which will substan- tially reduce or overcome the disadvantages of the known devices mentioned hereinabove and at the sametimewill allow being manufactured bysimple, reliable and economical means.

The said object is attained by the present invention which relates to a deflection device for deflecting a laser beam in thermal surface treatments on splined elements, characterized in comprising a first mirror on which it is arranged to impinge a laser beam generated by a repective source, and at least a second mirror on which the laser beam reflected by the said first mirror impinges and from which it is reflected so asto be directed towards a predetermined zone of the said splined element which has to be subjected to the said thermal surface treatment; the said first and second mirrors rotating during use with the same angular velocity about a respective axis of symmetry relative to which each of them is mounted inclined by an angle of predetermined value so that the laser beams impinging on the said first and second mirrors will describe an annulartrajectory on the surface of these latter, whilst the laser beam which strikes the said predetermined zone of the said splined element will described and oblate annulartrajectory substan tiallysimilarto a straight line segment.

Fora better understanding ofthe present invention a preferred embodiment therof will now be described byway of non limiting examplewith reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of a device according to the present invention, and Figure 2 is an elevational view of the device of Fig. 1, with some structural details.

Referring now in particularto Fig. 1, reference numeral 1 indicates a deflection device for deflecting a laser beam 2for carrying out a thermal surface treatment on a splined element 3. In the example shown, the element 3 is formed by a rack having a series of teeth 4which are parallel to each other and extend transversally through a section whose amplitude is indicated by "A". Each tooth 4 has two lateral surfaces Sjoined at the upper end by a top surface 6; whilst between adjacent teeth 4there are radiusing surfaces indicated by reference numeral 7.

According to the present invention, the device 1 comprises a first and a second mirror 11 and 12 respectively, which are rotated by a respective support shaft 13,14, and a stationary mirror 15 which receives the laser beam reflected by the mirror 11 and reflects this beam towards the surface ofthe mirror 12.

Each mirror 11,12 is partially inclined with respectto the corresponding shaft 13, 14, so thatthe opposed edges of the mirrors 11 and 12 each describe, during a rotation of 360", two circumferences indicated respec tivelybyreferencenumerals 16 and 17 forthe mirror 12 and by reference numerals 18 and 19 forth mirror 12. Thus, the zone in which the reflection of the laser beam 2 takes place, as regards the mirrors 11 and 12 results in being comprised between the planes defined bythecircumferences 16 and 17 and 18 and 19, respectively. In particular, as regards the mirror 11, the beam describes on the surface ofthis mirror, an annulartrace indicated by reference numeral 21.

Owing to the variation of the level of the plane of reflection during the rotation of the shaft 13, the beam 2 describes on the surface of the mirror 15 a trace in the form of a circumference. In particular, the beam 2 is indicated by a small circle which migrates clockwise along the said trace 22 atthe same speed of rotation as the shaft 13.

From the mirror l5the beam 2 is reflected onto the surface ofthe mirror 12 and covers a zone which includes substantially all the points situated between the circles delimited by circumferences 18 and 19 and The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

theannularcrown defined by the reflection of the circular trace 22 from the said mirror 15. In this way, the beam 2 describes on the surface of the mirror 12 an annulartrace 23 due to the combination of the relative movement ofthe beam 2 and the shaft 14. By making the shafts 13 and 14 rotate in opposed directions and with a relative predetermined phase, it is possible to obtain that the laser beam reflected by the mirror 12 describesastronglysquashed annulartrajectory indicated by reference numeral 24 in Fig. 1, which trajectory may substantially be compared to a segment of a straight line.

In Fig. 2 there are shown substantially all the parts of the device 1 which have been described with reference to Fig. 1. In particular, it can be noticed that the rotation of the shaft 13 is controlled by a motor 26 which, by means of four gears 27,28,29 and 30 and a belt 31 transmits, in a known manner, the movement to the shaft 14 thereby making this latter to rotate in the opposite direction with repect to the shaft 13, as has been specified hereinabove.

The coupling between each shaft 13, 14 and the respective mirror 11,12 is obtained by means of a respective attachment unit indicated generally by reference numerals 33 and 34which accomplishes both the function of allowing the adjustment ofthe angle (90 - Oi, and 90 - 82) which each reflecting surface ofthe mirror 11, 12 forms with the axis ofthe respective shaft 13,14, and the function of adjusting the relative phase between the mirrors 11 and 12, allowing at least one of them to be positioned with a predetermined angle with respect to the corresponding shaft 13,14.

In Fig. 2 there are indicated by "B", "C" and respectively the distance between the shafts 13 and 14; the distance between the central point of the mirror 11 and the surface of the mirror 15; and the distance between the central point of the mirror 12 and the surface of the element 3. Finally, at this latterthere are indicated, besides the trace 24, also some possible traces which the beam 2, reflected by the mirror 12 may describe on the surface of the element 3. In particular, by the side of each trace (shown by thin dashed lines) there is indicated a number(0"; 360"; 90"; 180"; 270") which corresponds to the relative phaseofthe rotary mirrors 11 and 12.

The operation ofthe device 1 is quite simple. First, of aIl,the shafts 13 and 14 are made to rotate preferably at a constant speed. Therefore, as can be clearly seen in Fig. the laser beam 2 impinges on a surface ofthe mirror 11 which moves sinusoidaly between a maximum and a minimum valueaboutthe distance indicated by "C". Accordingly, on the mirror 14 is formed the trace 22 along which the beam 2 runs in the clockwise direction atthe speed determined by the motor 26. Analogouslyto what has been described hereinabove with reference to the mirror 11, the surface of the mirror 12 also moves according to a sinusoidal type law but in a rotational direction opposed to that of the mirror 11.In particular, in the case in which the displacements ofthe reflecting zone ofthe mirror 11 covered by the beam take place according to a sinusoidal law and the displacements ofthe analogous zone ofthe mirror 12 which is covered by beam take place according to a cosinusiodal type law, it is obtained thatthe combination ofthe reflections gives rise substantially to a straight line segmentwhich corresponds to the segment 24 shown in Fig. 2. The amplitude of such segment may be adjusted by acting on the attachment units 33, 34so as to vary the angles 81 and 62, whilstthe position which this segment assumes is adjusted by acting, as said before, on the relative phase ofthe mirrors 11 and 12 by means of the adjustment units 33 and 34.

After having determined the orientation and the dimension of the segment 24, it is possible, with reference to Fig. 1, to determine the exact position of the segment relativetothe element3 by displacing the device 1 relative to the element 3 or vice versa, so as to make the length of the segment 24 coincide with the length "A" of the zone intended to be subjected to the treatment.

From the analysis ofthe characteristics of the device 1 conceived according to the teachings ofthe present invention the advantages which may be obtained are clearly apparent.

First of all, the device 1 is extremely flexible in that it allows to adjust in a simple way both the amplitude and the orientation of the squashed annular trace 24.

Furthermore,the performances ofthe device 1 are stable in the course of the time; because, indeed, they depend solely upon the geometry ofthe system and upon the good operation ofthe mechanical parts (gears, belt) orthe electrical parts (motor) which form the actuating portion ofthe device itself. It has also been noticed thatthe distribution ofthe power along the segment or annulartrace 24 presents slight peak values atthe ends and this results in being particularly advantageous in the case in which elements like those shown in Fig. 1 have to be treated. In fact, atthe ends of the teeth 4there is present a higher dispersion of heat, so thatto obtain a uniform treatment it is necessary to supply more thermal energy at such ends.

Finally, it is clear that modificatiions and variations may be made to the device 1 described hereinabove, without departing from the scope ofthe invention. For example, the presence ofthe stationary mirror is not essential, inasmuch as itispossibleto displace directly to its place the mirror 12, provided all the conditions of rotation and inclination specified hereinabove are observed.

Claims (6)

1. A deflection device for deflecting a laser beam for carrying out thermal surface treatments on splined elements, characterised in that it comprises a first mirror on which it is arranged to impinge a laser beam generated by a respective source, and at least a second mirror on which the laser beam reflected by the said first mirror impinges and from which it is reflected so as to be directed towards a predetermined zone of the said splined element which has to be subjected to the said thermal surface treatment; the said first and second mirrors rotating during use with the same angular velocity about a respective axis of symmetry relative to which each of them is mounted inclined by an angle of predetermined value; so that the laser beams impinging on the said first and second mirrors will describe an annulartrajectory on the surface of these latter, whiist the laser beam which strikes the said predetermined zone ofthe said splined element will describe an oblate annulartrajectory substantially comparable to a straight line segment.

2. A device as claimed in claim 1, characterized in thatlt cornprisesadíustment means for adjusting the said inclination of each said mirror relative to the respective axis of rotation.

3. A device as claimed in claim 1 or 2, characterized in that it comprises adjustment means for adjusting the relative phase between the said first and second mirrors.

4. A device as claimed in any ofthe preceding claims, characterized in that it comprises a third mirror which receivesthe laser beam reflected by the said first mirror and reflects the said beam onto the surface ofthe said second mirror.

5. A device as claimed in claim 4, characterized in thatthe said first and second mirrors are made to rotate by two respective shafts parallel to one another, and that the said third mirror is in an intermediate position and forward with respect to the said first and second mirrors.

6. Adeflectiondevicefordeflectinga laser beam for carrying out thermal surface treatments on splined elements, substantially as hereinbefore described with reference to the accompanying drawings.