Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-12-23
2004-03-30
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S829000
Reexamination Certificate
active
06714357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens drive system using a feed screw for moving one or more lens groups.
2. Description of the Related Art
An optical instrument such as a camera which is provided with a lens drive system using a feed screw for moving one or more lens groups is known in the art.
Such a lens drive system is provided with a feed screw shaft on which a male thread portion is formed, a nut member which is provided with a female thread portion which is engaged with the male thread portion of the feed screw shaft, a motor for rotating the feed screw shaft, and a lens frame or a lens holder for holding one or more lens elements. Rotating the feed screw shaft by the motor causes the lens frame to move together with the nut member.
In such a conventional lens drive system, if the feed screw shaft continues to be rotated by the motor until the lens frame or the nut member abuts against another member and stops thereby, the nut member and the feed screw shaft, which are engaged with each other, tightly fasten themselves on each other. This sometimes makes any further rotation of the feed screw shaft relative to the nut member impossible.
To prevent such a problem from occurring, it is generally the case that operation of the motor is controlled so that the motor stops rotating immediately after a position sensor senses that the lens frame has reached a predetermined stop position before the lens frame or the nut member runs over the stop position and abuts against another member.
However, there is a possibility that the position sensor cannot sense for some reason that the lens frame reaches a predetermined position. In this case, the feed screw shaft continues to be rotated by the motor until the lens frame or the nut member abuts against another member and stops thereby. As a result, the nut member and the feed screw shaft tightly fasten themselves on each other. This sometimes makes any further movement of the lens frame impossible.
Since one or more lens groups have been required to be moved by motor with a high degree of precision in recent years, there has been a tendency to reduce the pitch of the feed screw of the lens drive system. This tendency makes it easy to cause the nut member and the feed screw shaft to tightly fasten or lock themselves on each other.
SUMMARY OF THE INVENTION
The present invention provides a lens drive system which can reliably prevent the aforementioned problems which reside in conventional lens drive systems wherein the nut member and the feed screw shaft sometimes tightly fasten themselves on each other.
According to an aspect of the present invention, a lens drive system includes a lens frame having at least one lens element; a nut member which is secured to the lens frame, the lens frame and the nut member being movable in an optical axis direction without rotating relative to a base of the lens drive system, the direction of a screw hole of the nut member being parallel with the optical axis; a feed screw shaft having a male thread portion and a non-threaded portion, the male thread portion being engaged with the screw hole of the nut member so that the male thread portion is engaged with a female thread portion formed on an inner peripheral surface of the screw hole, a diameter of the non-threaded portion being smaller than an inner diameter of the screw hole; an engagement portion formed on the nut member, the engagement portion having at least one deformable screw-engaging portion which is engaged with the male thread portion; and a motor for rotating the feed screw shaft. The engagement portion is forced by rotation of the feed screw shaft to move in an axial direction of the feed screw shaft. The screw-engaging portion is disengaged from the male thread portion so that the male thread portion idles with respect to the engagement portion when a force greater than a predetermined value is applied to the engagement portion via the rotation of the feed screw shaft in the axial direction thereof. When the linear movement of the lens frame and the nut member is restricted during the rotation of the feed screw shaft to move the nut member and the lens frame in a direction from the male thread portion toward the non-thread portion, the engagement portion of the nut member remains on the male thread portion of the feed screw shaft while the female thread portion of the nut member is disengaged from the male thread portion of the feed screw shaft to move onto the non-thread portion of the feed screw shaft.
If the feed screw shaft is rotated in a rotational direction reverse to the predetermined rotational direction by the motor in a state where the female thread portion of the nut member is positioned on the non-thread of the feed screw shaft, the engagement portion can be forced by a reverse rotation of the feed screw shaft by the motor so that the female thread portion of the nut member moves back onto the male thread portion.
It is desirable for the portion of the engagement portion to be resilient so that the screw-engaging portion can be disengaged from the male thread portion.
The screw-engaging portion can include at least one thread ridge which is engaged with the male thread portion of the feed screw shaft.
The screw-engaging portion can includes at least two screw-engaging portions which are engaged with the male thread portion of the feed screw shaft from different directions.
The engagement portion can include a guide portion for preventing the screw-engaging portion from being disengaged from the male thread portion, the engagement portion being deformed to allow the screw-engaging portion to be disengaged from the male thread portion when the force exerted on the engagement portion becomes greater than the predetermined value.
It is desirable for the lens drive system to include a biasing member for biasing the lens frame in a second direction from the non-threaded portion toward the male thread portion. The nut member presses the lens frame to move the lens frame toward the non-threaded portion when the lens frame is driven to move in the direction from the male thread portion toward the non-threaded portion. The lens frame moves toward the male thread portion by a biasing force of the biasing member when the lens frame is driven to move in the second direction from the non-threaded portion toward the male thread portion.
The lens drive system can be incorporated in a camera having a stop-position controller for optically detecting an axial position of the lens frame, for driving the motor in accordance with the detected axial position of the lens frame, and for stopping the lens frame at a predetermined axial position. If the stop-position controller malfunctions, the lens drive system operates to avoid an adverse effect on the lens drive system due to the malfunction.
It is desirable for at least a portion of the engagement portion to be resilient so that the guide portion can bend resiliently to allow the screw-engaging portion to be disengaged from the male thread portion when the force exerted on the engagement portion becomes greater than the predetermined value.
The lens element, which is held by the lens frame, can include a focusing lens group of a photographing optical system.
The lens drive system can be incorporated in a zoom lens barrel. The lens element, which is held by the lens frame, can include a rearmost lens group serving as a focusing lens group of a photographing optical system. The base can be formed as a part of a housing of the zoom lens barrel.
It is desirable for the lens frame to be linearly guided in an optical axis direction without rotating about the optical axis.
The lens drive system can further include a linear guide mechanism for linearly guiding the lens frame in an optical axis direction without making the lens frame rotate relative to the base. The linear guide mechanism can include a guide shaft extending parallel to the optical axis. The nut member can include a guide recess in which the guide shaft is engaged to be slidable on
Greenblum & Bernstein P.L.C.
Mack Ricky
PENTAX Corporation
LandOfFree
Lens drive system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lens drive system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lens drive system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3287536