Optical: systems and elements – Lens – With support
Reexamination Certificate
2002-06-05
2004-03-23
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S822000, C359S823000, C359S814000, C359S696000, C359S698000, C348S357000, C396S079000, C310S332000
Reexamination Certificate
active
06710950
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a mechanism for moving the lens elements of an electronic camera.
BACKGROUND OF THE INVENTION
The components of electronic cameras require low power consumption, low weight and cost efficiency. These design criteria are challenged by the demand for optically adjustable cameras that provide autofocus, zoom optics, or both. These features require the relative movement of optical elements to provide the adjustment. The required motion is typically linear but may use a rotating motor combined with a motion-converting mechanism such as a lead-screw. The motion range is often in the order of millimeters. It is a purpose of this invention to provide a mechanism for adjusting the position of the optical elements in an electronic camera.
One component that has been used in numerous applications is a bimorph piezoelectric element, such elements are constructed of multiple layers of piezoelectric material wherein each layer is connected for independent excitation. In U.S. Pat. No. 4,291,958, a bimorph piezoelectric cantilever beam is used in combination with a magnifying lever for focusing a camera. However, the necessary stroke of such a focusing device results in a poor stiffness of the device. In electronic camera applications, space is a crucial factor. There is thus a need for simple drive elements that can operate in narrow spaces with limited mechanical support. It is a purpose of this invention to utilize a bimorph piezoelectric element to adjust the position of a lens in an optical system of a digital camera.
SUMMARY OF THE INVENTION
A miniaturized digital camera is constructed for use with a mobile communication device or other compact appliance. The optical system of such a camera may consist of a small lens assembly having single or multiple lens components. The optical system transmits the image received from an external source to a sensor array which converts the optical signal to a digital signal for processing. In multiple lens configurations, the lenses in the optical system are moved in relation to each other to provide autofocus and zoom capability.
In the simplest of applications a single primary lens may be provided with sufficient movement to provide autofocus in accordance with the sensed location of the subject. For simplicity the subject invention is first described with reference to a single adjustable lens application, although multiple lens configurations may be constructed utilizing multiple drive mechanisms as disclosed in this application.
According to this invention, a lens element is mounted within a camera on a tubular member. The lens tube is in turn mounted on a support tube for movement along the longitudinal axis of the tubular member. The adjustment movement is provided by means of multiple bimorph piezoelectric elements, for example by three elements, spaced symmetrically around the circumference of the support tube. The piezoelectric elements are connected to and mounted on a flexible printed circuit board which may contain other electronic components associated with the lens drive system. The flexible printed circuit board is mounted on the support tube and is in turn connected to a voltage source such as a battery. The flexibility of the printed circuit board allows it to be formed to the shape of the support tube and for the piezoelectric element to be positioned in engagement with the lens tube.
The bimorph piezoelectric element used in the subject mechanism is constructed of at least two layers of piezoelectric material which are independently energized to provide relative deformation between the two layers. The piezoelectric element used in the system of one embodiment of this invention is formed in the shape of a beam having an engagement pad extending transverse to the plane of the element from its midpoint. The beam is fixed to the circuit board close to ends or nodal positions. The outer end of the engagement pad is free to move in operative association with the movable lens tube. In the preferred embodiment, the beam comprises a pair of bimorph piezoelectric elements extending to either side of the engagement pad. Each of the bimorph elements have dual active layers. The differential deformation generated by energizing only one of the two layers will cause the piezoelectric elements to bend, moving the outer end of the engagement pad into contact with the movable lens tube. By altering the excitation of the piezoelectric elements, the engagement pad causes movement in an axial direction, thereby adjusting the position of the lens. A pattern of excitation is devised to provide movement in discrete steps.
A processor is connected in the printed circuit board to provide the main control for the digital camera and is constructed to generate a drive voltage pattern in accordance with the desired movement of the lens.
The movement generated by the piezoelectric element provides a high resolution, but there are no structural features that provide a reference in order to obtain accurate repeatability. The step length provided by the piezoelectric element can vary with operational and environmental conditions. In order to obtain the precision required in some optical designs, a position sensor is used to monitor the position of the movable tubes. An optical sensor is used to view a reflecting surface which is mounted on the moveable tube. The reflecting surface consists of a gray-scale incorporated into the surface treatment of the moveable tube. This configuration will provide accurate positional monitoring of a moveable tube.
In a second embodiment of this invention a pair of lenses are used to provide a zoom function. In this embodiment the moveable tube is divided into a front lens support section and rear lens support section and each of the sections is driven separately by piezoelectric elements in a manner similar to that described above. If the application warrants, an optical sensor can be provided to monitor the position of both sections.
Further embodiments can be constructed which combine the autofocus and zoom functions.
In this manner a miniature drive system is provided to move the lens within the camera while using a minimum of power and space.
REFERENCES:
patent: 5101278 (1992-03-01), Itsumi et al.
patent: 5633763 (1997-05-01), Suzuki et al.
patent: 5675444 (1997-10-01), Ueyama et al.
patent: 6437485 (2002-08-01), Johansson
Ahlgren Pentti
Johansson Stefan
Kauhaniemi Ilpo
Mattsson Christer
Rouvinen Jarkko
Ben Loha
Nokia Mobile Phones Limited
Perman & Green LLP
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