JPH03294811A - Lens moving device - Google Patents

Abstract

PURPOSE:To use a low-torque motor and to reduce the hysteresis of the movement of a lens frame to the rotation of the motor by pressing a small-sized engagement member having an engagement part capable of coupling with the screw part of a driving shaft and an abutting member which is provided successively at a specific interval to the engagement member and does not engage the screw part of the driving shaft against the driving shaft. CONSTITUTION:A racking part 27 which engages the screw part of the driving shaft 21 and the abutting part 30 which is juxtaposed at a specific interval to the racking part 27 and abuts on the screw part of the driving shaft 21 without engagement are arranged while pressed against the driving shaft 21, and another press-contacting member 31 is arranged halfway between the racking member 27 and press-contacting part 30 opposite about the driving shaft 21 while pressed against the driving shaft so that the force is held balanced in the opposite direction from the pressing direction. Consequently, the low- torque motor is usable and the hysteresis is prevented from being generated in focusing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a lens moving device for a video camera, an electronic still camera, etc., in which a rack member connected to a lens is moved linearly by rotation of a drive shaft to perform automatic focus adjustment. Regarding.

2. Description of the Related Art Conventionally, the basic configuration of a photographing lens system in a video camera or the like consists of a front lens group (focusing lens group), a compensator lens group, a variator lens group, and a master lens group. A method for adjusting the focus of a video camera equipped with such a photographic lens system is to slightly vibrate the master lens group in the photographic lens system using a ceramic actuator, etc., and measure the high-frequency component level of the signal obtained from the image sensor. A method was used in which the front and rear focus was detected by the camera, and the feedback was fed back to the lens drive system to adjust the position of the front lens group so that the image was sharpest (National Technical Report 3).
(See Vol. 1, No. 6, 1958, pp. 65-67).

Recently, a device that can perform both optical path length microvibration and focusing has been proposed (see Japanese Patent Application Laid-Open No. 1-265215). Focus adjustment has come to involve moving lenses other than the front lens, such as the master lens. There is. The configuration of such a conventional lens moving device will be described below with reference to FIG. 4. As shown in the figure, outer cylinder 1
holds an inner cylinder 3 to which a master lens group 2 is fixed so as to be slidable in the optical axis direction, and a pole bearing 4 is inserted between the outer cylinder 1 and the inner cylinder 3. stepping motor 5
The drive shaft 6 provided in the drive shaft 6 is held at its tip by a guide plate 7 for steadying, and the movable piece 8 screwed onto the drive shaft 6 and the inner cylinder 3 are connected by an arm 9. With the above configuration,
As the stepping motor 5 rotates, the moving piece 8
The master lens group 2 moves linearly and is fixed to the inner tube 3.
is moved in the optical axis direction to adjust the focus.

Problems to be Solved by the Invention However, in the above configuration, it is necessary to apply grease or the like to the threaded portion in order to improve the slidability between the drive shaft 6 and the movable piece 8. Since the stepping motor 5 is in contact with the drive shaft 6, the load on the stepping motor 5 increases due to the viscosity of the grease, and the temperature characteristics at low temperatures also worsen, requiring a high torque motor, which is important for video cameras used outdoors. There was a problem in that the elements such as power consumption, weight, volume, etc. increased. Also, a clearance is required between the drive shaft 6 and the movable piece 8 for sliding, and this clearance causes hysteresis in the movement of the master lens group 2 with respect to the rotation of the stepping motor 5. When moving, the lens does not move at all even if the stepping motor rotates by a small angle, and the lens does not move accurately in response to the stepping motor's rotation angle, resulting in hunting and unstable focusing operation. There was also.

The present invention solves the above problems, and aims to provide a lens moving device that can use a low-torque motor and can prevent hysteresis during focusing.

Means for Solving the Problems In order to achieve the above object, the present invention has a rack part that engages with the threaded part of the drive shaft, and a rack part that is attached to the threaded part of the drive shaft at a predetermined distance. The abutment parts that abut without engaging are arranged so as to press the drive shaft as one body, and at the same time, another pressure contact member is placed between the rack part and the pressure contact part at a position opposite to the drive shaft with respect to the drive shaft. The drive shaft is pressed against the drive shaft from the opposite direction while maintaining force balance.

Function The present invention reduces the contact area between the drive shaft and the rack member moving on the drive shaft with the above-described configuration.
Even if the viscosity of the grease interposed between the two increases, the load on the drive motor can be prevented from increasing, and a low-torque drive motor can be used.

Furthermore, since the rack member is pressed against the drive shaft, the threaded part of the rack member and the threaded part of the feed screw part of the drive shaft always mesh with each other without any gaps, and even if the drive shaft repeats forward and reverse rotations, the threads between the screw gears will cause The so-called crash that occurs is suppressed to a minimum.

In addition, since a separate member presses the drive shaft in a direction that cancels out the force of the rack member, the force is balanced in the direction perpendicular to the axis of the drive shaft, and the drive shaft is not subjected to excessive stress.
Therefore, the load on the drive shaft bearing does not increase.

EXAMPLE Hereinafter, a lens moving device according to an example of the present invention will be described with reference to FIGS. 1 to 3.

In FIGS. 1 and 2, focusing lenses 11 and 12 are fixed to a lens frame 13 made of resin by heat caulking or the like. Two guide balls 15 and 16 are provided inside the fixed lens barrel 14, and the hole-shaped grooves 13a and 13b at one end of the lens frame 13 are connected to the guide ball 15 and the U-shaped groove at the other end of the lens frame 13. 13c is slidably engaged with the guide ball 16, so that the focusing lens 11.12 is movably guided in the direction of the optical axis 17. Lens frame 1
3 is a rack unit engaging member 18 (details will be described later)
is fixed with screws 19, and rack unit 1
The tip of 8 engages with a drive shaft 21 of a stepping motor (drive means) 20.

Grease (not shown) is applied to the surface of the threaded portion of the drive shaft 21. The drive shaft 21 is a stepping motor 20
The drive shaft 21 is held in the direction of the thrust bearing 24 by a plate spring (not shown) provided inside the stepping motor 20. This prevents the drive shaft 21 from wobbling in the thrust direction. The stepping motor 20 is fixed to the fixed lens barrel 14 via a guide plate 23 with screws 25 and 26.

Next, details of the rack unit 18 will be explained. In FIG. 3, a rack part (engaging part) 27 made of resin having approximately the same thread pitch as the thread pitch of the drive shaft 21 is connected to a plate 28.
The rack portion 27 is pressed against the drive shaft 21 from one side by a plate spring 28. On the rack part 27 side, there is a contact part 30 that comes into contact with the threaded part of the drive shaft 21.
is provided integrally with the rack portion 27 at a predetermined interval, and is pressed against the drive shaft 21 by a spring (pressing means) 28 . The contact portion 30 has a flat surface so as not to engage with the threaded portion of the drive shaft 21 . Further, on the opposite side of the rack portion 27, a resin pressing piece 31 is fixed to the tip of a leaf spring 32, and the leaf spring 32 biases the pressing piece 31 toward the drive shaft 21 side. Further, the pressing position of the pressing piece 31 is set near the middle between the pressing positions of the rack part 27 and the contact part 30. The plate spring 28 and the plate spring (pressing means) 32 have approximately the same urging force; the force of the rack part 27 and the contact part 30 pressing the drive shaft 21 and the force of the pressing piece 31 pressing the drive shaft 21. By balancing these, the radial load on the metal bearing 22 of the stepping motor 20 and the stick slip between the lens frame 13 and the guide balls 15, 16 are reduced. The leaf spring 28 and the leaf spring 32 are attached to the lens frame 13, and are integrally joined together with a reinforcing plate 33 by spot welding or the like. The reinforcing plate 33 is provided with positioning holes 34 and 35, and the projections 36 of the lens frame 13 are provided with positioning holes 34 and 35.
．． It is inserted in 37.

The operation of the lens moving device configured as described above will be described below.

The steering/sopping motor 20 is configured to rotate 9 degrees per pulse, and the thread pitch of the drive shaft 21 is 0.
．． Since it is set to 4m, the stepping motor 20
When rotates by one pulse, the drive shaft 21 rotates by 9 degrees, the rack portion 27 engaged with the drive shaft 21 moves by 10 μm, and the rack portion 27 is integrally fixed to the lens frame 13 by the plate spring 28. Therefore, the focusing lenses 11 and 12 are also aligned with the optical axis 1.
Move 10 μm in the direction of 7. At this time, the rack section 27
Since the contact portion 30 presses the drive shaft 21 over a long span, the plate spring 28 is not twisted (the motor 20
The hysteresis of the movement of the lens frame 13 with respect to the rotation of the lens frame 13 can be reduced, and as the stepping motor 20 rotates in the forward and reverse directions, the focusing lenses 11 and 12 follow it and move back and forth to perform the focusing operation. It can be done.

As described above, according to this embodiment, the contact area of the rack member that presses against the drive shaft of the stepping motor is small, and the drive shaft is pressed evenly from both sides in a direction perpendicular to the axis, so that stepping It is possible to provide a lens moving device in which the load on the motor is reduced, a low-torque motor can be used, and hysteresis is prevented from occurring.

Although a stepping motor is used as the motor in the embodiment, a brushless DC motor or the like may also be used.

Effects of the Invention As is clear from the above embodiments, according to the present invention, there is provided a small engaging member having an engaging portion capable of engaging with a threaded portion of a drive shaft, and a small engaging member having a predetermined distance from the engaging member. Since the contact member that is placed in parallel and does not engage with the threaded part of the drive shaft is pressed against the drive shaft, the contact area between the feed screw part of the drive shaft and the rack member is small, and the load due to the viscosity of the grease is increased. This makes it possible to use a low-torque motor, resulting in low power consumption, small size, and light weight. In addition, since the rack member is pressed against the feed screw part by a separate member in a direction that cancels out the pressing force, the stick slip against the movement guide member in the optical axis direction of the lens frame is reduced, and the lens frame against the rotation of the motor. It is possible to reduce the hysteresis of the movement of the lens, thereby achieving excellent effects such as being able to perform focusing operations accurately.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main parts showing the configuration of a lens moving device according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the main parts of the device, and FIG. 3 is a diagram showing the drive shaft and rack unit of the same device. FIG. 4 is a plan view of the main part showing the engaged state, and a sectional view of the main part of a conventional lens moving device. 11.12...Focusing lens (lens), 13.
... Lens frame, 17 ... Optical axis, 18 ...
...Rack unit (engaging member), 20...
・Stepping motor (drive means), 21...
Drive shaft, 27... Rack part (engaging part), 28.
...Plate spring (first pressing means), 30...
・Contact part, 31... Pressing piece, 32...
Leaf spring (second pressing means).

Claims (1)

[Claims] A lens frame holding a lens and movably guided in the direction of the optical axis, a drive shaft having a feed screw portion, a drive means for driving the drive shaft, and an engagement member capable of engaging with the screw portion of the drive shaft. In the lens moving device, an engaging member having a portion, and a lens moving device in which the engaging member and the lens frame are combined, are arranged in parallel with the engaging portion at a predetermined distance and engaged with a threaded portion of the drive shaft. a contact portion that does not match; a first pressing means for pressing the engaging portion and the contact portion against the drive shaft; and a first pressing means for pressing the drive shaft in a direction opposite to the pressing force of the first pressing means. A lens moving device including a second pressing means.