WO2008053427A1

WO2008053427A1 - Actuator assembly and opto-mechanical device comprising an actuator assembly

Info

Publication number: WO2008053427A1
Application number: PCT/IB2007/054399
Authority: WO
Inventors: Johan F. Lurquin; Robby F. Maes; Johannes F. M. Willemse
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-11-02
Filing date: 2007-10-30
Publication date: 2008-05-08

Abstract

An actuator assembly (100) comprising a first part (2), a second part (3), a guide (5,6) for guiding motion of the first part (2) relative to the second part (3) along a main axis in response to a driving force, and an electro-magnetic unit (11,20) for generating the driving force between the first part (2) and the second part (3) in response to a driving signal. The guide (5,6) comprises a spring (15,16), which is mechanically connecting the first part (2) and the second part (3) and which allows for motion of the first part (2) relative to the second part (3) along the main axis in response to the driving force. This allows for relatively simple and energy-efficient positioning of the first part (2) relative to the second part (3).

Description

Actuator assembly and opto-mechanical device comprising an actuator assembly

FIELD OF THE INVENTION

The invention relates to an actuator assembly comprising a first part, a second part, a guide for guiding motion of the first part relative to the second part along a main axis in response to a driving force, and an electro-magnetic unit for generating the driving force between the first part and the second part in response to a driving signal.

The invention also relates to an opto-mechanical device comprising a lens body and an actuator assembly.

BACKGROUND OF THE INVENTION Examples of such an assembly and device are known. US-Al -2004/0234258 discloses a lens driving device and imaging device. A driven body has an optical lens, a sleeve on one side and a slot on the opposite side, so as to sandwich a light axis together with the sleeve. Further, a guide shaft is a shaft fitting into the sleeve in order to cause the driven body to move along the direction of the optical axis. The guide shaft is a shaft inserted as a brace at the slot and is for preventing the driven body from rotating taking the guide shaft as a center. A flat coil is fixed to the driven body. The position of the driven body is detected by a position detection magnet fitted to the driven body and a magneto -resistive element arranged in a non-contact manner spaced from the magnet. When current flows in the drive coil, thrust parallel with the optical axis direction is generated. Frictional resistance generated between the driven body and the guide shafts becomes fixed because the thrust direction and drive direction are always parallel over the entire region of the drive stroke. Drive characteristics and servo characteristics can be made superior.

A disadvantage of the known assembly is that it has a low energy efficiency because the servo control to keep the driven body positioned constantly consumes power.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an assembly and device of the types defined in the opening paragraphs that allow for relatively simple and energy-efficient positioning of the first part relative to the second part of the actuator assembly. The invention is defined by the independent claims. Advantageous embodiments are defined by the dependent claims.

This object is achieved by means of the actuator assembly according to the invention, which is characterized in that the guide comprises a spring, which is mechanically connecting the first part and the second part and which allows for motion of the first part relative to the second part along the main axis in response to the driving force. The mechanical spring allows for motion of the first part relative to the second part in response to the driving force and further provides for a fixed relative position of the first part with respect to the second part in case no driving force is present. In the absence of a driving signal, the spring ensures that a static force is maintained, and that the relative position of the first part with relation to the second part remains constant without consuming power resulting in an improved energy efficiency.

In an embodiment of the actuator assembly according to the invention, the electro-magnetic unit for generating the driving force comprises an electrically conductive coil, attached to one of the first and second parts, for generating a magnetic field in response to the driving signal acting on a permanent magnet, which is attached to the other of the first and second parts. This variant is simple in construction. In a further embodiment the electrically conductive coil is attached to the first part and the spring provides for an electrical connection between the electrically conductive coil and a portion of the second part. In this way, a robust electrical connection is provided to the movable coil thereby avoiding the risk of wearing out and breaking the normally used electrical wiring.

In another embodiment of the actuator assembly according to the invention, the permanent magnet comprises at least one pair of permanent magnets, having a first magnetized zone and a second magnetized zone, which are positioned in a line, and wherein respective components of magnetization of the first and second magnetized zone parallel to the line are oriented in opposite directions. The first and second magnetized zone, that are oriented in opposing directions, result in an increased efficiency of the permanent magnet and therefore in a more energy-efficient actuator assembly.

In an embodiment of the actuator assembly according to the invention, the actuator assembly further comprises a position measuring sensor attached the other of the first and second parts for measuring a displacement of the first part with respect to the second part as a result of the driving force. This provides for a simple construction in which the relative position of the first part with respect to the second part is controlled. In an embodiment, the spring comprises a spring washer. This variant is simple in construction, since the spring washer is a well-known spring that has a simple mechanical construction and is easy to attach to other components. Furthermore, the spring washer allows for motion along one main axis, and is rigid along other axes, thereby advantageously providing for a movement of the first part relative to the second part along one main axis only.

According to another aspect of the invention, there is provided an optomechanical device comprising a lens body and an actuator assembly according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be further elucidated and described with reference to the drawings, in which:

Fig. 1 is an exploded view of an embodiment of an actuator assembly according to the invention;

Fig. 2 is a schematic cross-section of a pair of permanent magnets of an actuator assembly according to the invention;

Fig. 3 is a perspective view of the actuator assembly of Fig. 1; Fig. 4 is a perspective cross-sectional view of the actuator assembly of Fig. 1. Fig. 5 is a perspective view of an embodiment of a guidance component of an actuator assembly according to the invention; and

Fig. 6 is a perspective view of another embodiment of a guidance component of an actuator assembly according to the invention.

The Figures are not drawn to scale. In general, identical components are denoted by the same reference numerals in the figures.

DETAILED DESCRIPTION OF EMBODIMENTS

Implementations of actuator assemblies in opto-mechanical products will be explained below as an example. The description will focus on the field of imaging optics for small applications, such as web cameras, including those integrated in Liquid Crystal Display (LCD) flat panel displays, for mobile phones, Personal Digital Assistants (PDAs), etc. In camera's, for instance, the actuator assembly can be used for autofocus movement, optical zoom, mechanical shutter actuation, diaphragm opening control, compensation of tilt between optics and imager, x-y movement of an image sensor to compensate for camera shake, etc. More generally the actuator assembly finds application in any field in which an actuator assembly allowing small displacements and requiring low forces to hold the movable parts in position is useful. This includes the field of magnetic and/or optical recording, for example. It also includes applications in toys, such as remotely controlled model cars and planes, game controllers with tactile feedback, etc. Another field of application is that of industrial and/or automotive equipment, e.g. to operate proportional valves for fluids and gasses, mass flow controllers, etc. Yet another field of application is in lighting, to focus small bundles of light, for example by moving a lens in front of a bright Light Emitting Diode (LED). The assembly and method of driving it are particularly suited to mobile applications, where low power consumption is an issue.

In Figs. 1, 3 and 4 an actuator assembly 100 comprises a first part and a second part, in this example formed as a barrel 2 and a housing 3, respectively. The barrel 2 is movable with respect to the housing 3. In the example (see Fig. 4), the barrel 2 carries a lens body 4. The barrel 2 carries a lens assembly comprising more than one lens in other embodiments.

The barrel 2 is linearly guided to allow focusing of an optical system comprising the lens body 4. To this end, the housing 3 comprises a guide, in this example in the form of a first guidance component 5 and a second guidance component 6. The first and second guidance components 5,6 comprise, in this example, first spring washers 15 and second spring washers 16, respectively, attached to a ring. Preferably, the first and second spring washers 15,16 are made from an electrically conducting material, for example a metal. In this example the first guidance component 5 comprises four spring washers 15 and the second guidance component 6 comprises also four spring washers 16. The ring of the first guidance component 5 is mechanically attached to the top of the barrel 2, and the ring of the second guidance component 6 is mechanically attached to the bottom of the barrel 2. The first spring washers 15 of the guidance component 5 are, for example with their respective ends, mechanically attached to the top of the housing 3, and the second spring washers 16 of the guidance component 6 are, for example with their respective ends, mechanically attached to the bottom of the housing 3. In this way a fixed position of the barrel 2 relative to the housing 3 is provided in case no driving force is applied. Furthermore, this construction allows for a relatively unconstrained movement of the barrel 2 in a direction along the longitudinal axis of the barrel 2.

To displace the barrel 2 in the direction determined by the first and second guidance components 5,6, the actuator assembly 100 comprises an electrically conductive coil 11 , which is attached to the barrel 2 in this embodiment. The electrically conductive coil 11 comprises terminals (not shown) for applying a driving signal, such as a driving voltage or a driving current. The electrical connection to the terminals is provided for by the first and second spring washers 15,16 thereby allowing for relatively large displacements of the barrel 2, since there are no wires connected to the barrel 2 and the electrically conductive coil 11. Current passing through the electrically conductive coil 11 gives rise to a magnetic field acting on a cylindrical pair of permanent magnets 20 that is attached to the housing 3 and is separated from the electrically conductive coil 11 by a small gap. The use of an electromagnetic unit for establishing a field of force has the advantage of requiring fewer components. It should be noted that other types of permanent magnets can be applied, such as for example a single permanent magnet. Furthermore, in another embodiment of the actuator assembly permanent magnet 20 is attached to the barrel 2 and the electrically conductive coil 11 is attached to the housing 3.

The pair of permanent magnets 20 comprises a first magnetized zone 12 and a second magnetized zone 13, separated by a transition zone 14, as is shown in Figs. 1 and 2. The transition zone 14 is preferably made of a material that has a high magnetic permeability. In another embodiment the first and second magnetized zones 12 and 13 adjoin and no transition zone is present. As is shown in Fig. 2, which is a schematic cross-section of the pair of permanent magnets 20, the first magnetized zone 12 has a magnetization M in a direction parallel to the direction of motion of the barrel 2, which is along the axis of symmetry of the pair of permanent magnets 20. The second magnetized zone 13 has a magnetization MM in a direction parallel to the direction of motion of the barrel 2, which is opposite to the direction of the magnetization M of the first magnetized zone 12. The effect is that the pair of permanent magnets 20 produces magnetic flux lines perpendicular to its face and also provides opposite north and south poles in a direction parallel to the direction of motion of the barrel 2. The opposite direction of the magnetizations M and MM of the first and second magnetized zones 12 and 13, respectively, wherein the, for example, north pole of the first magnetized zone 12 is adjacent to the north pole of the second magnetized zone 13, provides for a high concentration of magnetic flux lines in the region of both north poles, where the first and second magnetized zones 12 and 13 are adjacent, thereby increasing the energy-efficiency of the actuator assembly 100. The construction of the pair of permanent magnets 20 allows the above-mentioned effect to be achieved without the use of a yoke. The overall configuration is relatively compact, and provides for a reduction of the number of parts of the first actuator assembly 100. A displacement of the first part with respect to the second part can be measured by a position measuring sensor (not shown). Different types of sensors can be used, such as, for example, optical reflector types and magnetic field sensor types. In an embodiment of the actuator assembly a measurement can be made of the displacement between the housing 3 with the permanent magnet and the barrel 2 equipped with the position measuring sensor, such as for example a hall sensor. The displacement of the pair of permanent magnets 20 generates a voltage in the hall sensor, which is a function of the relative distance between the hall sensor and the pair of permanent magnets 20. Alternatively, an additional permanent magnet is provided on the housing 3, which is dedicated for use with the hall sensor and which may be smaller than the pair of permanent magnets 20.

The actuator assembly 100 can be driven in an easy way. The actuator assembly 100 is provided with an electro -magnetic unit for providing a driving force acting to move the barrel 2 relative to the housing 3 in a direction parallel to the longitudinal axis of the barrel 2 and the housing 3. Thus, the first and second spring washers 15,16 prevent motion of the barrel 2 relative to the housing 3 when no current is passed through or voltage is applied over the electrically conductive coil 11. This enables the barrel 2 to be displaced in steps relative to the housing 3 using a current, which can be increased or decreased in stepwise or continuously. The movement of the barrel 2 is a function of the applied current and of the forces exerted by the first and second spring washers 15,16. The first and second spring washers 15,16 ensure that the position held by the barrel 2 is maintained when no driving force is applied. After a stepped movement of the barrel 2, it is possible to determine the distance of the actual travel using a position-measuring sensor (e.g. a hall sensor). If the distance shows a deviation from the intended step, the current can be adapted to correct the distance of a next step. With a substantially constant, and thus predictable, force exerted by the first and second spring washers 15,16 that opposes motion of the barrel 2, open- loop control becomes possible. This simplifies the driver construction, compared with stepper motors and piezo drives. It will be appreciated that the direction of movement of the barrel 2 relative to the housing 3 is changed by changing the polarity of the current that is applied.

Alternative embodiments of the first and second guidance components 5,6 are shown in Fig. 5 and Fig. 6. Fig. 5 shows a first spring configuration 30, which comprises a top ring 31 which is mechanically connected to a first ring segment 32, a second ring segment 33 and a third ring segment 34. The three ring segments 32, 33, 34 are, for example, each with their respective ends mechanically attached to the barrel 2, and the top ring 31 is mechanically attached to the housing 3. Fig. 6 shows a second spring configuration 40, which comprises five parts, a bottom ring 41, which is mechanically connected via a first ring segment 42, a second ring segment 43 and a third ring segment 44 to the top ring 31. The bottom ring 41 is, for example, mechanically attached to the barrel 2, and the top ring 31 is mechanically attached to the housing 3.

In summary, the invention provides for an actuator assembly comprising a first part, a second part, a guide for guiding motion of the first part relative to the second part along a main axis in response to a driving force, and an electro-magnetic unit for generating the driving force between the first part and the second part in response to a driving signal. The guide comprises a spring, which is mechanically connecting the first part and the second part and which allows for motion of the first part relative to the second part along the main axis in response to the driving force. This allows for relatively simple and energy- efficient positioning of the first part relative to the second part.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. Actuator assembly (100), comprising a first part (2), a second part (3), a guide (5,6) for guiding motion of the first part (2) relative to the second part (3) along a main axis in response to a driving force, and an electro-magnetic unit (11,20) for generating the driving force between the first part (2) and the second part (3) in response to a driving signal, wherein the guide (5,6) comprises a spring (15,16), which is mechanically connecting the first part (2) and the second part (3) and which allows for motion of the first part (2) relative to the second part (3) along the main axis in response to the driving force.

2. Actuator assembly according to claim 1, wherein the electro-magnetic unit for generating the driving force comprises an electrically conductive coil (11), attached to one of the first and second parts (2,3), for generating a magnetic field in response to the driving signal acting on a permanent magnet (20), which is attached to the other of the first and second parts (2,3).

3. Actuator assembly according to claim 2, wherein the electrically conductive coil (11) is attached to the first part (2) and the spring (15,16) provides for an electrical connection between the electrically conductive coil (11) and a portion of the second part (3).

4. Actuator assembly according to claim 2, wherein the permanent magnet (20) comprises at least one pair of permanent magnets, having a first magnetized zone (12) and a second magnetized zone (13), which are positioned in a line, and wherein respective components of magnetization of the first and second magnetized zone (12,13) parallel to the line are oriented in opposite directions.

5. Actuator assembly according to claim 1, wherein the actuator assembly further comprises a position measuring sensor attached to one of the first and second parts (2,3) for measuring a displacement of the first part (2) with respect to the second part (3) as a result of the driving force.

6. Actuator assembly according to claim 1, wherein the spring (15,16) comprises a spring washer.

7. Opto -mechanical device comprising a lens body (4) and an actuator assembly (100) according to any one of claims 1 to 6.