GB2421086A - Suspension system with two non parallel hinged linkages for lens - Google Patents

Abstract

A suspension system 20 comprises two non-parallel hinged linkages 14, 15. Each linkage allows movement of eg a lens 21 only in the plane perpendicular to the hinges within that linkage. As the two linkages are non-parallel, movement of the lens is constrained to the line of intersection of the two movement planes. The suspension may be used to suspend a lens in a camera to allow movement of the lens along the optic axis for example during focussing or zooming. The suspension may be made as a plastic moulding, possibly integral with the lens barrel, forming a compact suspension suitable for use in a miniature camera, as used for example in portable devices such as mobile phones. Each hinged linkage comprises two link elements 16, 17, 18, 19 and three parallel hinges 111-113, 114-116. Support structure 12, moving piece 13 and lens barrel 22, 36 are shown. The suspension system may be moved using piezoelectric actuator 37.

Description

Camera Lens Suspension

FIELD OF THE INVENTION

This invention pertains to suspension systems for suspending an object to allow movement along a movement axis. It is particularly suited to a suspension system for suspending an object which is a lens, for example as used in a camera system which may be employed in a mobile telephone or a mobile digital data processing and/or transmitting device.

BACKGROUND

In recent years, with the explosive spread of portable information terminals known as PDAs and portable telephones, an increasing number of models incorporate a compact digital camera or digital video unit employing a CCD (charge-coupled device) or CMOS (complementary metaloxide semiconductor) sensor as an image sensor. When such a digital camera or the like is miniaturized using an image sensor with a relatively small effective image-sensing surface area, its optical system also needs to be miniaturized accordingly.

To achieve focussing or zooming, additional drive motors have to be included in the already confined volume of such miniature cameras. Whilst most of the existing cameras rely on variations of the well-known electric-coil motor, a number of other actuators have been proposed as small drive units for the lens system. These novel drive units may include transducers based on piezoelectric, electrostrictive or magnetostrictive material. These transducers or actuators are commonly referred to as electro-active.

Small electro-active actuators with comparably large translation displacements have been recently built using a helical structure of coiled piezoelectric bender tape.

Such twice-coiled or "super-helical" devices are found to easily exhibit displacement in the order of millimetres on an active length of the order of centimetres. These structures and variations thereof are described, for example, in the co-owned published international patent application WO-0147041 or by D. H. Pearce et a! in: Sensors and Actuators A 100 (2002) , 281 -286. They are manufactured from multilayer ceramic base material such as lead zirconate titanate (PZT) and sintered at high temperatures into their final shape. The use of such actuators as drive motors for lens systems is described for example in the co-owned published international patent application WO-02/10345 1.

As drive units adapt to the reduced volume of the compact camera designs, lens suspensions systems, which constrain the motion of the lens holder, have to co- evolve. Lens suspension systems ideally have a low stiffness, resistive force or friction in the direction of the desired motion and high stiffness in all other directions.

An example of such a suspension system is described in co-owned international patent application PCT/GBO4/00278 1. The suspension system described comprises, at its simplest, a form of four-bar link or parallelogram suspension, in which a pair of pivoted parallel links constrain a moving object to remain parallel to a support structure. Motion along the optic axis is accompanied by a much smaller sideways, or off-axis, movement. In autofocus applications, this off-axis movement has a negligible effect on the image quality. However, in zoom applications, the necessary axial movment is larger, so that the off-axis movement may be significant. This is particularly the case in high-resolution cameras where the sideways movement represents several pixels, reducing the image quality.

It is therefore a purpose of the present invention to provide a suspension for movement of an object along a movement axis with minimal off-axis motion.

SUMMARY OF THE INVENTION

In a first aspect therefore, the invention provides a suspension system for suspending a movable piece to allow movement of the movable piece along a movement axis, the suspension system comprising: a support structure two hinged linkages, each hinged linkage comprising two link elements and three parallel hinges, the three hinges connecting respectively: the support structure to the first link element; the first link element to the second link element; and the second link element to the movable piece wherein the hinges are all perpendicular to the movement axis, and the hinges of the first linkage are not parallel to the hinges of the second linkage.

The movable piece moves relative to a support structure. The movable piece may be the object itself, for example a lens barrel holding one or more lenses, or it may be a suitably shaped connecting piece, for example a collar designed to fit in an appropriate groove in the lens barrel. The support structure likewise may be the support itself, for example the case of a camera module, or a connecting piece designed to fit in the support structure.

The suspension comprises two non-parallel hinged linkages. Each linkage alone allows movement of the movable piece in one plane only, that is, the plane normal to its hinge axes. The two movement planes of the two non-parallel linkages intersect at a line which is normal to the hinge axes of both linkages. Movement is therefore constrained to this line only, which is the movement axis. Movement along the movement axis is not accompanied by any sideways or off-axis movement. In the case of a camera, the movement axis is the optic axis of the lens system, allowing a lens or lenses to be moved along the optic axis, as is required for example in focussing or zooming. It is another feature of the suspension of the invention that the support piece and the moving piece remain in the same orientation; if the support piece and moving piece are planar and parallel to each other, they remain parallel.

The linkages are non-parallel, that is, they are disposed at an angle to each other. The linkages may be at any angle to each other, but an angle of 90 degrees provides the most rigid arrangement, that is, the arrangement with most resistance to sideways motion. Preferably the centre of mass of the object to be moved lies close to, or coincident with, the movement axis (defined as the line of intersection of the movement planes of the two linkages), as this arrangement minimises tilting forces.

Additional linkages may be provided to further increase the rigidity. For example, the suspension may comprise three linkages disposed at 120 degrees around the movable piece, or four linkages disposed at 90 degrees. Such arrangements are symmetrical and improve the resistance to twist and tilt around the movement axis.

The linkages each comprise two link elements. Preferably, each link element has the form of a rectangular plate whose length is greater than, or comparable to, its width which is greater than its thickness. Within a linkage, the two link elements may be identical. Alternatively, they may differ, for example, one link element may be longer than the other. Similarly, the two or more linkages of a suspension may be identical or may differ, for example in positioning of the hinges.

The link elements are hinged at both ends. The hinge is a pivotal connection, that is, a connection which allows relative rotation of two members about the axis or line of the hinge or pivot. The hinge may be a conventional hinge comprising a pin extending through locating holes in both members. Preferably however the hinge is a flexure, that is, a piece of material able to flex elastically. For example, the two link elements may be formed as a single piece of material which is reduced in thickness along the desired hinge line. On application of an appropriate force, the locally thin material bends to allow relative rotation of the thicker, stiffer portions on either side.

Preferably all the hinges of the suspension system are flexures.

All the elements of the suspension may be formed integrally from one piece of material, preferably a plastics material, for example selected from a group including polypropylene, polyethylene and polyamide (nylon). This is advantageous in that the suspension is robust and easily manufactured, for example by injection moulding. The pivotal connections are formed by portions of the piece of material having a smaller thickness than the remainder of the piece of material.

Each linkage comprises two link elements and three hinges. As the movable piece is made to move up and down (along the movement axis) the link elements change their angle to the movement axis and the hinge connecting the links moves sideways (normal to the movement axis). Where space is limited, additional link element-hinge pairs may be provided; the sideways motion is then shared by more than one hinge. For example, a linkage comprising two link elements and three hinges may connect to a further hinged link element. There are then two inter-link hinges which both move sideways, one outwards and one inwards. This may be an advantage where the space on the outside of the linkage is limited, as the outward motion is not as great as with only a single inter-link hinge.

The greater the width of the linkages, as measured by the length of the hinges, the greater the resistance to tilting of the movable piece. Preferably, the length of the hinges is a considerable proportion of the corresponding dimension of the moving object. For example, if the moving object is a lens barrel, the length of the hinges is preferably a considerable proportion of the diameter of the lens barrel, that is, the length of the hinges is preferably more than half the diameter of the lens barrel and more preferably more than 80% of the diameter of the lens barrel.

The suspension constrains the movement of the object along the movement axis. In the case of a miniature camera, the suspension constrains the movement of the lens barrel along the optic axis. The movement is driven by an actuator.

Preferably the actuator is a piezoelectric actuator of the type known as a Helimorph, which is a helical structure of coiled piezoelectric bender tape. Preferably the coil extends in a sector of a circle around the lens barrel. One end is fixed to the support structure while the other, moving, end is fixed to the lens barrel. On activation, the Helimorph actuator drives the lens barrel up and down along the optic axis. The Helimorph actuator may be conveniently located between the lens barrel and the linkages of the suspension of the invention.

The suspension is particularly suitable for suspending a lens in a miniature camera in which the suspension system suspends a movable lens piece to allow movement of the lens piece along the optic axis.

A miniature camera is a camera for use in, for example, a portable electronic device such as a mobile telephone, a personal digital assistant (PDA), a lap-top computer and the like. Miniature cameras are also used in for example security cameras and computer cameras such as web-cams. Such cameras are digital; that is, the lens system forms an image on an electronic sensor, such as a CCD or CMOS sensor. These miniature digital cameras are considerably smaller than conventional cameras, the lens diameter being less than about 10 mm as compared to up to 15mm or more in non-miniature cameras. Typical lens diameters in miniature cameras are 5 mm - 8 mm, while the complete camera module (which includes a casing, the lens system, the image sensor and any actuator(s) and suspension) for applications in portable devices is generally required to have outer dimensions of less than about 15 mm and a volume less than about 2 cm3. The suspension of the invention is particularly suited to such small devices, as it is compact, readily manufactured as a single component (or few components) and easy to assemble into a camera module.

The suspension allows movement of a lens piece. The lens piece moves along the optic axis; that is, it moves relative to the image sensor, the casing of the device or other lenses. The lens piece may be a single lens, a lens holder holding a lens, a group of lenses, a lens barrel containing one or more lenses, or any other part of the lens sytem of a camera. It may be the entire lens system.

The suspension allows movement of a lens piece relative to a support structure. The support structure may be the casing of the camera module or it may be another part of the lens system. For example, the suspension may link two parts of a lens barrel, each holding one or more lenses, allowing relative movement between different lenses or lens groups.

Non-limitative examples of the suspension of the invention are described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.! is a perspective drawing of an example of the suspension of the invention; Fig.2 is a further example of the suspension of the invention suspending a lens barrel; Fig.3A and 3B show a top view and a vertical cross-section respectively of a suspension of the invention suspending a lens barrel; Fig.4 is a schematic showing a suspension of the invention and an additional link element; Fig.5 is a plan view of a suspension of the invention with 3 linkages; Fig.6 is a schematic of a suspension of the invention forming part of a lens barrel; Fig.7 shows a suspension of the invention with link elements of unequal lengths; Fig.8 Shows a suspension of the invention hinged inwardly; and Fig 9 shows a suspension of the invention with non-identical linkages.

DETAILED DESCRIPTION

Figure 1 shows an embodiment of the suspension system 11 of the invention. The support structure 12 is connected to the movable piece 13 by two hinged linkages 14 and 15. The first linkage 14 comprises two link elements 16 and 17 connected together at hinge 111. The lower link 16 is connected to the support structure 12 by hinge 112 and the upper link 17 is connected to the movable piece 13 by hinge 113.

The three hinges 111, 112 and 113 of the first linkage 14 are parallel to each other and parallel to imaginary axis y. The first linkage 14 therefore constrains any point in the linkage 14 and the movable piece 13 to move only in the x,z plane. Likewise, the second linkage 15 comprises link elements 18 and 19 and hinges 114, 115 and 116.

The hinges 114, 115 and 116 are parallel to each other and to the imaginary x axis.

Points in the second linkage 15 and the movable piece 13 are therefore constrained to move only in the y,z plane. Since the movable piece 13 is connected to both linkages 14 and 15, it is constrained to move only along the line common to both planes x,z and y,z, that is, the z direction. The suspension 11 therefore allows free movement in the up-down direction (z), denoted by the double headed arrow 117. Movement in any other direction is severly restrained by the stiffness of the linkages.

Figure 2 shows another embodiment of the suspension of the invention in which the suspension 20 is manufactured as an integral plastic moulding with reduced thickness at the lines of the hinges, forming flexures. The reduction in thickness in Figure 2 appears as a cut or notch on the inside of the moulding. The notch could equally well be on the outside of the moulding or the material could be notched both inside and outside to leave a thin piece in the middle (as shown in Figure 3B below).

In any of these cases, the reduction in thickness along the hinge1 line causes the suspension to flex preferentially along these lines. Other features of Figure 2 are similar to those of Figure 1 and like numerals are used. Figure 2 also shows a lens 21 and lens barrel 22 connected to the moving piece 13 of the suspension. The optic axis is denoted by a dotted line. The suspension 20 allows the lens barrel 22 to move up and down along the optic axis.

Figures 3A and 3B show schematic top and cross-sectional views of an embodiment of the invention as used in a miniature camera. In Figure 3A, top view, the moving piece 13 is connected to four linkages 3 1,32,33,34. The outer perimeter of the moving piece 13 is square, while the inner perimeter 35 is circular (shown as a dotted line), shaped to fit in a groove around the lens barrel 36. A Helimorph piezoelectric actuator 37, shown as a long-dashed outline, fits around the lens barrel 36, within the confines of the linkages 3 1-34. At one end the actuator 37 ends in a first tab 38, which is the fixed end attached to the case of the device (not shown). At the other end, the actuator 37 ends in a tab 39 attached to the lens barrel 36, to effect movement of the lens barrel.

Figure 3B is a cross section through the right-hand half of the camera assembly of Figure 3A taken along the line A-A'. The linkage 31 links the movable piece 13 to the support structure 12. The support piece is fixed in the case 41, shown hatched, of the camera module. The Helimorph actuator 37 is shown in the space between the linkage 31 and the lens barrel 36. Also shown is the image sensor 42 attached to the case 41.

In the camera module of Figures 3A and 3B, the lens diameter is 5 mm and the diameter of the lens barrel is 7 mm. The length of the lens barrel is 7 mm. The thickness of the linkages is 0.7 mm except at the hinge parts where the thickness is 80 microns. The length of the link elements is about 3 mm and the width is about 7 mm (equal to the length of the hinges). On focussing, movement of the lens along the optic axis is up to 300 micron, causing a sideways movement of the central hinge of the suspension of about 250 microns. In a zoom camera, lens movements of up to 3 mm along the optic axis are required and sideways motion of the suspension (at the central hinge) may be 1 mm or more, depending on the dimensions of the suspension.

The camera module shown in Figures 3A and 3B forms a device which is neat and compact, which is important in miniature cameras for use in portable electronic devices such as mobile phones. The suspension system is easy to manufacture as a plastic moulding and easy to assemble as it comprises few, possibly only one, components. The several plastic mouldings of the device, notably the lens barrel, the case and the suspension can all be manufactured to high dimensional accuracy and can readily be accurately positioned relative to each other, for example by moulded-in locating pins and sockets or by use of suitable jigs during glueing of the ends of the suspension system in place. The provision of the non-parallel hinged linkages of the invention constrains movement of the lens barrel accurately along the optic axis only, providing high quality images in zoom ad autofocus applications and in high resolution cameras.

Further variants of the suspension of the invention are shown in the schematic drawings of Figures 4-9.

Figure 4 is a schematic cross-section of a suspension of the invention in which each linkage is connected to the support structure by a further hinged link element.

Two linkages 31 and 33 are shown; the suspension also includes two further perpendicular linkages not visible in this cross-section. The linkage 31 comprises link elements 4 1,42 (shown as single lines) and hinges 43,44,45 (shown as open circles), and connects a moving piece 13 to a support structure 12 via a further link element 46 and hinge 47. The other linkages are similar. The benefit of this arrangement is that the additional link element allows smaller sideways extent and smaller sideways movement of the linkage compared to the arrangement of Figure 2 for example.

Figure 5 shows a plan view of a vanant of the suspension of the invention comprising three linkages 5 1,52,53 disposed at 120 degrees about a moving piece 54.

Such a suspension is symmetrical and balanced.

Figure 6 is a schematic cross-section of an example of the suspension of the invention in which the suspension forms part of the lens barrel itself allowing relative movement between two lens groups. Two linkages 31 and 33 are shown; two further perpendicular likages are not visible in the cross-section. The lens barrel in this case comprises two parts, an upper part 61 and a lower part 62 connected by the four linkages. In this case, the lower part 62 of the lens barrel forms the support structure of the suspension. The upper part 61 carries a single lens 63 while the lower part carries two lenses 64 and 65. Other numbers of lenses are also possible. The suspension allows relative movement between the first lens group 63 (single lens) and the second lens group 64,65 when driven by an actuator (not shown). Such relative movement is necessary for example to maintain focus during zooming.

In a further variant, a second suspension of the invention may link the lower part of the lens barrel 62 of Figure 6 to a fixed support such as a casing. The first suspension and actuator then provide relative movement between the two lens groups while the second suspension and actuator provide relative movement between the entire lens system and the casing. Again, such relative movements are necessary to maintain focus during zooming.

Further variants are shown schematically in Figures 7 to 9, in which the link elements differ. In Figure 7 the two link elements 72 and 73 forming the linkage 71 are of unequal length. In Figure 8 the linkage 81 bends inwards rather than outwards.

In Figure 9, the two linkages 91 and 92 are not identical, the link elements of linkage 91 being of equal length and those of linkage 92 being of unequal length. Such variations in link elements serve to allow freedom to design the linkages to best fill the space available. (Note that the suspension systems of Figures 7-9 include further linkages (not shown) in addition, in which the hinges are not parallel to the hinges of the linkages shown).

It will be apparent that many other arrangements of lenses and suspension systems fall within the scope of the invention.

Claims (8)

1. A suspension system for suspending a movable piece to allow movement of the movable piece along a movement axis, the suspension system comprising: a support structure two hinged linkages, each hinged linkage comprising two link elements and three parallel hinges, the three hinges connecting respectively: the support structure to the first link element; the first link element to the second link element; and the second link element to the movable piece wherein the hinges are all perpendicular to the movement axis, and the hinges of the first linkage are not parallel to the hinges of the second linkage.

2. A suspension system according to Claim 1 in which the movable piece is a lens piece.

3. A camera including a suspension system according to Claim 2.

4. A suspension system according to preceding claims including one or more additional linkages.

5. A suspension system according to Claim 4 wherein the linkages are disposed symmetrically about the movement axis.

6. A suspension system according to preceding claims made of moulded plastic.

7. A suspension system according to Claim 6 made as a single piece of material.

8. A suspension system according to preceding claims wherein the hinges are flexures.