Optical: systems and elements – Lens – With variable magnification
Patent
1997-03-24
1998-10-06
Epps, Georgia Y.
Optical: systems and elements
Lens
With variable magnification
359700, 359823, G02B 1514, G02B 702
Patent
active
058186484
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical instrument with a focusing mechanism designed to eliminate backlash. The present invention is described with particular reference to a focusing mechanism for a borescope or endoscope used for viewing a location inaccessible to or remote from the user but is applicable to other types of optical instrument.
BACKGROUND OF THE INVENTION
In order to provide a focused image for the user, there is normally provided at the proximal or "user" end of the instrument a housing or chassis member containing a focusing lens mounted in a cylindrical focusing lens cell, and a focus control member. The focusing lens cell is slidably received within the chassis and linked to the focus control member such that rotation of the focus control member moves the focusing lens cell axially so that a focused image can be provided for the user's eye or at the CCD in a CCTV camera or the film plane in a still camera.
Typically, the focus control member comprises a sleeve rotatably mounted on the chassis and having a helical groove in its interior surface. A pin projecting radially from the focusing lens cell extends through an axial slot in the chassis wall and engages in the helical groove. Accordingly, rotation of the focus control member causes axial movement of the focusing lens cell within the chassis.
For free movement of the focus control member and focusing lens cell, there have to be clearances between the components. Inevitably, this results in the phenomenon known as backlash. As the focusing control member is rotated one way or the other, the focusing lens cell only moves when all the clearances have been closed. Typically, the focus control member will have to be rotated by more than 3 degrees before the focusing lens cell starts to move. This is not usually a problem to the user of general borescopes. However, if the rotational position of the focus control member is required to be directly related to the position of the focusing lens cell, these clearances represent inaccuracy and unacceptable performance.
SUMMARY OF THE INVENTION
The present invention seeks to provide an anti-backlash focusing mechanism for an optical instrument in which the above mentioned clearances between the focus control member and the focusing lens cell are eliminated.
Accordingly, the present invention provides a focusing device for an optical instrument comprising focusing lens means mounted in a first cylindrical member located in a cylindrical bore in a housing, the first cylindrical member being slidable and constrained to move axially within the bore; focus control means comprising a sleeve rotatably mounted on the housing and a first coupling mechanism between the sleeve and the first cylindrical member whereby rotation of the sleeve causes axial movement of the first cylindrical member; the device further comprising a second cylindrical member also located in the bore of the housing adjacent to the first cylindrical member and being slidable and constrained to move axially with the bore; a second coupling mechanism between the sleeve and the second cylindrical member whereby rotation of the sleeve causes axial movement of the second cylindrical member synchronously with movement of the first cylindrical member; first biasing means urging the first and second cylindrical members towards each other to eliminate clearances between them and the sleeve and between the first and second cylindrical members and the housing and means to prevent relative axial movement between the sleeve and the housing.
Preferably, the first cylindrical member is constrained to move axially within the bore by means of a first pin projecting radially outwardly from the first cylindrical member and extending through a first axial slot in the wall of the housing.
The first coupling mechanism between the first cylindrical member and the sleeve preferably comprises a first helical slot formed in the sleeve in which the first pin engages.
Similarly, the second cylindrical member may be constrained
REFERENCES:
patent: 3506338 (1970-04-01), Holderbaum
patent: 4255020 (1981-03-01), Yukio
patent: 4386829 (1983-06-01), Sumi
patent: 4506952 (1985-03-01), Grollimund
patent: 5515205 (1996-05-01), Yokoyama et al.
Epps Georgia Y.
Keymed (Medical & Industrial Equipment) Ltd.
Mack Ricky
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