Driving device

Details Driving device Driving device

1999-07-01

2001-04-10

Ben, Loha (Department: 2873)

Optical: systems and elements

Lens

With support

C359S822000, C359S698000

Reexamination Certificate

active

06215605

ABSTRACT:

This application is based on application Nos. H10-187070, H10,187071 and H10-192608 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving device for driving a plurality of driven members in the same direction or in opposite directions, and particularly to a driving device having a driving element and a driving rod provided for each of driven members so that the driven members can be driven individually.
2. Description of the Prior Art
To drive a plurality of driven members along the same line while keeping them in a predetermined positional relationship, it is customary to drive all of the driven members by means of a single driving element combined with a guide mechanism that guides the driven members along the driving direction while controlling their relative positions. For example, in a zoom lens system, helicoids having different pitches are provided, as a guide mechanism, on a lens barrel, so that, by converting the rotation amount of a motor into different driving amounts for individual movable lenses, the movable lenses are kept in a predetermined positional relationship. This makes it possible to vary the focal length while keeping the focal point fixed.
In recent years, it has been becoming increasingly common to keep driven members in a predetermined positional relationship by providing a driving element and a driving rod for each of a plurality of driven members so that the driven members are driven individually and the outputs of the driving elements are adjusted individually. A driving device based on this principle requires a greater number of driving elements, but does not require a complicated guide mechanism that demands high precision. Accordingly, a driving device of this type can be realized with a simple structure, and is thus particularly suitable for cases where light-weight driven members are driven by small amounts.
As an example of driving device having a driving element and a driving rod provided for each of driven members,
FIG. 29
shows a driving device designed for use in a taking lens system of a digital camera. This driving device
16
is for driving two movable lenses LA and LB included in a zoom lens system.
The driving device
16
is composed of two piezoelectric actuators
51
and
52
serving as driving elements, two driving rods
53
and
54
, and one guide rod
55
. The piezoelectric actuators
51
and
52
are, at their rear-end surface, individually fixed to two base blocks (not shown), and the driving rods
53
and
54
are fixed to the front-end surface of the piezoelectric actuators
51
and
52
. The piezoelectric actuators
51
and
52
, when a voltage is applied thereto, expands or contracts along the direction connecting their front-end and rear-end surfaces in accordance with the magnitude of the voltage applied. The driving rods
53
and
54
are arranged parallel to each other, and the guide rod
55
is arranged below the mid line between the driving rods
53
and
54
and parallel thereto.
The lenses LA and LB are individually held in lens frames
56
and
57
. The lens frames
56
and
57
have projections
56
a
and
57
a
formed in their obliquely upper portion, and through these projections
56
a
and
57
a
are formed through holes through which the driving rods
53
and
54
are placed. The lens frames
56
and
57
also have projections
56
b
and
57
b
formed in their lower portion, and in these projections
56
b
and
57
b
are formed grooves that engage with the guide rod
55
. In a side surface of the projection
56
a
of the lens frame
56
, an opening is formed through which a portion of the driving rod
53
is exposed, and a plate spring
56
c
is provided by which the portion of the driving rod
53
exposed through the opening is pressed with an adequate force. By the pressing force of the plate spring
56
c
, the inner surface of the through hole formed through the projection
56
a
is kept in slidable contact with the driving rod
53
. Although not shown in
FIG. 29
, the projection
57
a
of the lens frame
57
has the same structure, so that the inner surface of the through hole formed through the projection
57
a
is kept in slidable contact with the driving rod
54
. The wall surfaces of the grooves formed in the projections
56
b
and
57
b
of the lens frames
56
and
57
are kept in loose slidable contact with the guide rod
55
so as to prevent rotation of the lenses LA and LB.
A piezoelectric actuator, when the voltage applied thereto varies abruptly, expands or contracts abruptly and, when the voltage applied thereto varies gradually, expands or contracts gradually. As the piezoelectric actuators
51
and
52
expand or contract, the driving rods
53
and
54
are displaced. The lens frames
56
and
57
, which are kept simply in slidable contact with the driving rods
53
and
54
, follow the displacement of the driving rods
53
and
54
when the displacement is slow, but cannot follow the displacement and thus remain where they are when the displacement is fast.
Accordingly, by causing an abrupt rise followed by a gradual drop repeatedly in the voltage applied to the piezoelectric actuators
51
and
52
, it is possible to drive the lenses LA and LB in one direction; by contrast, by causing a gradual rise followed by an abrupt drop repeatedly in the voltage, it is possible to drive the lenses LA and LB in the opposite direction. The speed at which the lenses LA and LB are driven can be adjusted by varying the magnitude and the cycle of the voltage applied.
By controlling the voltage applied to the piezoelectric actuators
51
and
52
individually and thereby driving the lenses LA and LB individually, it is possible to keep the lenses LA and LB in a predetermined positional relationship.
However, in the above-described driving device
16
, in which a driving element and a driving rod are provided for each of driven members, the driving elements, and also the driving rods, are arranged parallel to each other, and therefore the driven members can be driven not through the whole length of the driving rods but through only a portion thereof. This means that the driving rods are unnecessarily long, occupying unduly large spaces.
When piezoelectric actuators are used as driving elements, even though the driving rods are made of a highly rigid material, it is impossible to eliminate elastic deformation completely. For this reason, the longer the driving rods, the more difficult it is to drive the driven members efficiently because of absorption of the driving force from the piezoelectric actuators and delay in transmission of the driving force. Moreover, this leads to loss of energy. Furthermore, the longer the driving rods, the more rigid they need to be. This narrows the choice of the material of the driving rods and increases their cost.
To achieve efficient displacement of the driving rods, the rear-end surfaces of the piezoelectric actuators need to be fixed securely so that their expansion and contraction are transmitted to the driving rods without loss. For this reason, the base blocks, to which the piezoelectric actuators are fixed, are made of stainless steel, which is a heavy, rigid material. However, in the driving device
16
described above, the piezoelectric actuators are fixed to separate base blocks, and this makes the driving device
16
unduly large.
One way to increase the weight of the base blocks without making the driving device larger is, as shown in
FIG. 30
, by fixing both of the piezoelectric actuators
51
and
52
to a single, integrally-formed based block
60
that is approximately twice as large as one conventional base block. However, in a driving device of this type, the expansion and contraction of one piezoelectric actuators are transmitted, as vibration, to the other piezoelectric actuator through the base block, and this may adversely affect driving. For example, such vibration causes variations in the driving amount among the driven members even

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