This invention relates to an optical inspection instrument comprising a housing, a mirror mounted on the housing, and illumination means provided on the instrument for illuminating an object to be inspected by the instrument.

It is known to provide optical inspection instruments of the above type for dental use having a light source which emits light to illuminate an ^" . object, which light first undergoes reflection from the surface of the mirror before passing to the object. The illuminated object is then viewed by an observer by further reflection ^~ & ^~ the surface of the mirror. Since the surface of the mirror is already illuminated directly by the light source, the viewing of the illuminated object via the mirror takes place against an illuminated background which adversely affects the quality of the image received by the observer. It is also known, for medical and dental use, to provide an optical inspection instrument (in the form of a small handpiece) which has a reflecting mirror which transmits the image of an illuminated object e.g. a decayed tooth to an observer. However, in order to illuminate objects to be .inspected, it is necessary to provide a separate light source. In dental use, this frequently takes the form of a fixed lamp which can be adjusted so as to direct light into the mouth of a patient. This lamp is usually located some distance away from the patient, in order not to encumber the dentist, and it is not therefore readily possible to obtain the same degree of illumination of all areas of the inside of the mouth to be inspected. This problem may be overcome by the use of a separate, hand-held torch-like device which can be inserted in the mouth of a patient to provide strong illumination of the areas which cannot be illuminated properly by the fixed lamp, but this also encumbers the dentist unduly who will have the torch in

one hand and a dental mirror in the other hand.

There is, therefore, the need to provide an optical inspection instrument which provides satisfactory viewing of an illuminated object without the necessity to provide a separate light source.

According to the invention there is provided an optical inspection instrument comprising an elongate housing, a mirror mounted obliquely relative to the axis ^• of the housing for reflecting the image of an illuminated object to an observer who is holding the instrument, and illumination means provided on the instrument to illuminate an object to be inspected, characterised in that said illumination means is arranged on the instrument so. as to emit light transversely of the axis of the housing to illuminate an object directly without the light first undergoing reflection from the surface of the mirror.

The optical inspection instrument of the invention may be used to inspect parts of machinery which otherwise have to be dis-assembled to enable a proper inspection to be carried out. The length of the housing will be "selected according to the required depth of insertion of the instrument into a piece of machinery.

The instrument is also useful in the medical field, in dentistry, and has veterinary and industrial u

Preferably, the illumination means is formed as a unit which is removably mounted in the housing. The unit may comprise a power pack, and a bulb assembly detachably connected to the power pack. Conveniently, the power pack comprises a casing in which a storage battery can be received, and the bulb assembly comprises a metal sleeve detachably connected at one end to the casing and provided at its opposite., end with a- socket to receive a bulb. When the illumination means is mounted in the elongate housing, the bulb is located substantially in registry with a light outlet formed in the wall of the elongate housing, the light outlet being located near, or

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closely adjacent to the mirror. In order to protect the bulb e.g. to prevent a patient biting the bulb (when the medical instrument is a dental instrument), it is preferred that a transparent protective sleeve e.g. a small piece of glass tube, is mounted over the bulb and the metal sleeve in which the bulb is mounted.

Conveniently, the mirror and the light outlet are arranged at or near one end of the elongate housing of the instrument, and a switch arrangement is provided within the housing which is operable by a portion of the casing which projects from the opposite end of the housing.

For dental use of the instrument, at least parts thereof should be made of material suitable to render the instrument readily sterilisable. Therefore, at least the housing and the dental mirror should be made of sterilisable materials. Also, preferably at least part of the instrument is waterproof.

One embodiment of optical inspection instrument according to the invention will now be described in detail, by way of example only, with reference to.the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of the mode of use of the instrument;.

Figure 2 is a side view of a housing part of the instrument ;

Figure 3 is a diagrammatic and exploded view of illumination means and an electrical power pack which is removably mountable in the housing o.f Figure 2; and

Figure 4 is a detail view of the illumination means.

Referring now to Figure 1 of the drawings, the optical inspection instrument is designated generally by reference numeral 10 and comprises an elongate housing 11, a reflecting mirror 12 mounted obliquely relative .to the axis of the housing 11 for reflecting the image of an illuminated object 13 to an observer who is holding the instrument. Illumination means is arranged at the end of the housin 11 adjacent to the mirror 12 so as to emit

light rays 14 transversely of the axis of the housing 1 to illuminate the object 13 directly without the light first undergoing reflection from the surface of the mirror 12, Accordingly, the surface of the mirror 12 wil be relatively "dark" to the eye of the observer, so tha the image of -the illuminated object which is reflected by the surface of the mirror 12 will be seen clearly by the observer. Referring now to Figure 2 of the drawings, there is shown the housing 11 and the mirror 12 which i constructed in the manner of a dental mirror and is removably mounted on an inclined end portion 15 of the housing 11. A cut-out 16 is provided at the end of the housing 11 adjacent the mirror 12, and illumination mea 17 is located within the confines of the cut-out 16. The edge defining the cut-out 16 is formed in such a wa that light rays emitted by the illumination means 17 ex generally transversely of the axis of the housing 11 an -θ light rays, or no appreciable quantity of light impinges on the surface of the mirror 12.

The illumination means 17 comprises the he-ad a bulb which is provided at one end of a metal sleeve 1 which is shown diagrammatically in Figure 2 making electrical contact with. a contact element 19. The natu of the contact between the sleeve 18 and the contact element 19 is shown in more detail in Figure 3. A transparent protective sleeve 20 is housed removably within end of the housing 11 and serves to protect the illumination means. Thus, when the instrument is used in dentistry, the sleeve 20 will protect the bulb from being biten by a patient. Also, the sleeve enables the housing to be sterilised without the necessity to remov the illumination means. The instrument is provided with its own built in power pack to supply electrical power to the bulb' _. and this is formed as a unit which is removably mounted in the housing 11. The power pack comprises a casing

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21 having an external thread 22 which is engageable with an internal thread 23 provided at the end of the housing 11 remote from the mirror 12. The casing 21 is illustrated in Figure 3 accommodating a pair of dry cell batteries 24, and these may comprise any suitable commercially available batteries, or may comprise re¬ chargeable batteries if required.

A switch assembly 25 is removably mounted in the free end of the casing 21 and has an external screw-thread 26 which is received by an internal screw thread 27 provided in the end of the casing 21. The switch assembly 25 has a spring loaded contact 28 which makes firm contact with the end of the adjacent one of the batteries 24 as the assembly 25 is rotated. This maintains a strong electrical contact between the batteries 24 and the switch assembly 25 even before the metal sleeve 18 makes electrical contact with the switch assembly 25. In addition to the contact 19, the switch assembly 25 also has a projecting sleeve 29 which is internally threaded at 30 to receive the threaded end 31 of the metal sleeve 18. The sleeve 18 makes electrical contact with the switch assembly 25 by an end contact 32 which engages a projecting contact 33 of the switch assembly 35. An insulating spacer 34 separates the contact element 19 from the main body of the switch assembly 25.

• When the switch assembly 25 is positioned in the end of the casing 21, and the sleeve 18 is threaded in the sleeve 29,- an electrical circuit can be completed when the unit:'-" enters the housing 11 and the contact element 19 comes into abutment with an annular shoulder 35 (Figure 2) provided within the housing 11. This electrical contact will be achieved during the final turning of the casing 21 within the housing 11. However, before the power pack is inserted in position, the protective sleeve 20 is mounted in position over the metal sleeve 18 as shown in Figure 4. Furthermore, a stepped insulating bush 36 is located between the contact element 19 and the sleeve 20, and surrounds the

sleeve 29 (and the sleeve 18 housed within the sleeve 29). • Compression spring 37 is located between the bush 36 and the contact element 19, and surrounds the sleeve 29 and urges the bush 36 and the sleeve 20 to the left, as seen in Figure 4.

The purpose of the compression spring 37 is to locate the protecting sleeve 20 within the end of the housing 11 without any play, so that no rattling takes place. Also, the compression spring 37 provides a certain amount of "feel" during the final manipulation of the casing 21 within the housing 11 when the sleeve 20 is pressed towards the end of the housing 11. It will be appreciated that the on-off switching action will take place by the final manipulatory movements of the casing 21 so that the contact element 19 moves towards or away from the annular shoulder 35 of the sleeve 11.

The purpose of the insulated bush 36 , apart from transmitting thrust between the spring 37 and the sleeve 20, is to prevent premature completion of the electrical circuit as the powerpack enters the housing 11, which might otherwise occur due to electrical contact taking place between the sleeve 18 and the annular shoulder 35 or any other part ^' of the housing 11.

In order to prevent the penetration of moisture into the electrical parts of the instrument, an O-ring

38 is located on the sleeve 18 (see Figs.3 and 4) and is positioned between the adjacent ends of the sleeve 20 and the insulated bush 36.

The optical inspection instrument described above with reference to the drawings is particularly suitable for use as a dental inspection instrument, but . . may also be used, or adapted for use in general medicine. Similarly, the instrument may be used, or adapted for use, in other fields, such as the inspection of machinery. Conveniently, the powerpack , which is shown generally in Figures 3 and 4, may be of standard design, whereas different lengths of housing 11 may be provided to suit different uses. Thus, the length of the housing will be

increased when a greater depth of insertion of the instrument into a piece of machinery is required.

Accordingly, as will be evident from the fore¬ going disclosure, there is provided an optical inspection instrument which provides satisfactory viewing of an illuminated object, and improved over the known constructions, without the necessity to provide a separate light source.

In addition to use ^" for inspection or examination purposes in dentistry and medicine, the instrument may have veterinary use, or use in industry generally for inspection or examination purposes.