Camera with flexure focus mechanism

Abstract

A camera 1 has: a detector 2, a lensing assembly 3, and a flexure assembly 10. The detector outputs a signal indicative of light incident upon the detector. The lensing assembly directs incident light

Description

Technical Field of the Invention The present invention relates to focus mechanisms for cameras, especially portable or handheld infrared cameras and to flexures suitable to provide such focus 5 mechanisms. Background to the Invention Handheld infrared (IR) cameras typically comprise a lensing assembly and a detector aligned along an optical axis where the lensing assembly is operable to direct incident light on to the detector. A variable focus lens assembly may comprise different 10 lens elements and a mechanism to vary the separation between these elements so as to vary the focus. Typically, this mechanism may comprise corresponding coned metal elements with custom multi-start threads. This adds weight to the camera and requires some dexterity to operate. Accordingly, to save weight some IR cameras use a fixed focus lens assembly with a simplified focussing mechanism enabling the displacement 15 of the components of the lensing assembly relative to the detector to be varied, so as to vary the focus of the camera. On typical portable IR cameras, the focussing mechanism may comprise a linear rail system, threaded interconnection or the like. Such mechanisms are relatively straightforward to implement but are susceptible to unwanted pitch, roll and yaw 20 relative to the optical axis. This limits the precision of focus that can be achieved. Where the focus variation is controlled by manual manipulation of the mechanism, unwanted focus variation can occur when adjusting camera positioning. Whilst this can be alleviated by using motor controlled focussing mechanisms, these can add significant complexity and additional weight. In this context, a weight of l-2Kg is not 25 uncommon and thus maintaining alignment of the optical axis with a distant target, say 5km away, can be difficult. This can even be an issue when the camera is fitted to a tripod. It is therefore an object of the present invention to provide a focussing mechanism for use in a handheld IR camera that at least partially overcomes or 30 alleviates the above problems. 26 08 25 Summary of the Invention According to a first aspect of the present invention there is provided a camera comprising: a detector operable to output a signal indicative of light incident upon the detector; a lensing assembly operable to direct incident light onto the detector, the 5 lensing assembly having an optical axis aligned with the detector; and a flexure assembly operable to control variation of the displacement between the detector and the lensing arrangement along the said optical axis so as to vary camera focus; the flexure assembly comprising: a fixed portion; a moving portion spaced apart from the fixed portion; at least a pair of flexure elements spaced apart from one another and fitted 10 between the fixed portion and moving portion, the at least a pair of flexure elements adapted to permit movement of the moving portion relative to the fixed portion along a movement axis and to resist movement of the moving portion relative to the fixed portion along axes other than the movement axis; wherein the detector is located between the fixed portion and the moving portion and between the pair of flexure 15 elements. The use of a flexure assembly for focussing provides for precise control of linear displacement along the optical axis and minimal displacement along other axes or modes. A flexure assembly can additionally be relatively lightweight in construction. Preferably, the movement axis of the or each flexure element is aligned with 20 the optical axis of the lensing assembly. In this context, aligned may encompass substantially parallel optical and movement axes. The fixed portion may be fixed to a frame or housing of the camera. The lensing assembly may be mounted to the moving portion and the detector may be mounted to the fixed portion. Alternatively, the detector may be mounted to the moving portion 25 and the lensing assembly may be mounted to the fixed portion. It is beneficial to have the lensing assembly mounted to the fixed portion as this is typically heavier than the detector. The moving portion may be coupled to an actuator. The actuator may be a linear actuator. The actuator may be operable to move the moving portion relative to the fixed 30 portion. The actuator may be manually powered or may be or electrically powered. 26 08 25 Manually powered actuators may incorporate thumbwheels or the like to generate motion of the actuator from manual power. Electrically powered actuators may comprise electric motors, piezo electric elements, electromagnets or the like. The actuator may comprise an encoder such that actuator motion can be monitored. Suitable 5 encoders may be magnetic, optical, electronic, or mechanical as desired or as required. Suitable types of actuator include but are not limited to: a piezoelectric linear stage with magnetic linear encoder, an Encoded DC Geared motor, a manual lead screw operated via thumbwheel, or the like. The actuator may be controlled in response to a focus control system. The focus 10 control system may comprise a control unit operable to drive the actuator in response to control signals. The actuator may be operable to drive the moving portion to one or more pre-set positions. This can enable particular pre-set focus settings to be readily selected and implemented. The control signals may be output in response to user input. The user input may 15 be received via a user interface or one or more user input means. The user input means may comprise rotary switches, scroll wheels, push switches, toggle switches, touch sensitive switches or the like. Additionally or alternatively, the control signals may be generated by a camera control unit or relayed by a camera control unit in response to signals received from a remote device. This could allow operation of a camera in an 20 outdoor or inhospitable environment to be controlled by a user in an indoor or sheltered environment. The moving portion may be biased in a particular direction or toward a particular position. The biasing may be implemented by the provision of one or more biasing elements. In one embodiment, the or each biasing element may be a spring. 25 The fixed portion and moving portion may each comprise substantially flat structures. The flat structures may predominantly extend in planes substantially parallel to the movement axis. In one embodiment, the fixed and / or moving portions may each comprise a block with one or more slots. In another embodiment, the fixed and / or moving portions may each comprise a frame formed from one or more elongate rods. 26 08 25 Suitable flexure elements include but are not limited to flat shims, rods or shaped blocks as desired or as appropriate. Where the flexure assembly comprises two or more flexure elements, each flexure elements may be of the same type. Where the flexure element comprises a flat shim, the shim may be etched, 5 eroded or otherwise shaped from a sheet of material. In one example, the shim may be photo-etched. The shim may comprise a central aperture. This can permit passage of light and / or relative movement between the lensing assembly and detector past the shim. The shim may be provided with a stiffening element. The stiffening element may comprise a relatively rigid sheet bonded to said flat shim. In some such cases, the 10 stiffening element may be formed from a thicker sheet of material than the shim. Bonding may be achieved by suitable adhesive, welding or fasteners such as rivets, screws, bolts and the like as required or desired. Shims may be formed of any suitable material, typically a metal and in one example, steel or stainless steel. Where the flexure element comprises a rod, the rod may comprise one or more 15 sections of different diameter or stiffness. Sections of different diameter or stiffness may be formed by bonding different rod sections together. Bonding may be achieved by suitable adhesive or welding as required or desired. Such rods may be formed of a single material or may comprise sections formed of different materials as appropriate. Rods may be formed of any suitable material, typically a metal and in one example, 20 steel or stainless steel. Where the flexure element comprises a shaped monothetic block, the block may be shaped by a suitable erosion process from a simple basic form. Typically, the erosion process may be wire or spark erosion. The monolithic element may be formed of any suitable material, typically a metal and in one example, steel or stainless steel. 25 In a preferred embodiment, the flexure assembly may comprise two flat shims, each flat shim fitted between corresponding ends of the fixed portion and the moving portion; and wherein each flat shim is provided with an aperture aligned with a common movement axis of the flat shims. The detector may be provided between the flat shims and aligned with the optical axis. The lensing assembly may be provided at one end of 30 the flexure assembly. In such an assembly, the actuator may be provided on an opposing side of the moving portion to the flat shims. The detector may be operable to detect light in any suitable wavelength range. Suitable wavelength ranges my include infrared (IR), visible or ultraviolet (UV) wavelength ranges. In a preferred embodiment, the detector is operable to detect light in the IR wavelength range. 26 08 25 5 The detector may comprise an array of detecting elements. The lensing assembly may comprise a single lens or multiple lenses, as required or as desired. The detector may be mounted on a substrate, the substrate may be substantially planar. In such embodiments, the substrate may extend in a plane substantially perpendicular to the optical axis. In one embodiment, the substrate may comprise a 10 printed circuit board. The lensing arrangement can comprise one or more lenses. In some embodiments, the lensing arrangement may additionally or alternatively comprise one or more mirrors. The camera may be a handheld camera. In this context, a handheld camera may 15 comprise a camera adapted to be held by a user whilst capturing an image. This would equally apply to a camera suitable for handheld use, where the camera might typically be mounted on a tripod in use. Detailed Description of the Invention In order that the invention may be more clearly understood one or more 20 embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 Figure 2 25 Figure 3 Figure 4 Figure 5 is a schematic illustration of a camera according to the present invention; is a schematic illustration of a control architecture for camera according to the present invention; shows a flexure assembly according to the present invention; is an exploded view of a flat shim for a flexure assembly according to the present invention; is a schematic illustration of the range of motion achievable using the flexure of the present invention; 26 08 25 Figure 6 is a side view of the flexure assembly of figure 3 integrated into a camera according to the present invention; and Figure 7 is a perspective view of the flexure assembly of figure 3 integrated into a camera according to the present invention. 5 Turing now to figure 1, an infrared camera 1 comprises a detector 2 operable to output a signal indicative of light incident upon the detector 2; and a lensing assembly 3 operable to direct incident light onto the detector. The lensing assembly has an optical axis O aligned with the detector 2. In order to focus light from the lensing assembly on the detector, the displacement D between the detector 2 and the lensing assembly 3 can 10 be varied. In the present invention, the displacement D is varied by use of a flexure assembly (not shown in figure 1). This provides a relatively lightweight mechanism and precise control of linear displacement along the optical axis with minimal displacement along other axes or modes. The displacement D, can be controlled by a manual displacement mechanism. 15 More typically, as illustrated schematically in figure 2, the displacement D is controlled by an actuator 4. As shown in figure 2, operation of actuator 4 is in response to a control unit 5. The control unit 5 operation may be automated or be in response to operation of user input means 6 such as buttons, switches dials and the like. In many embodiments, the control unit 5 may also control a display unit 7 providing user 20 feedback on the image captured by detector 2 and / or focussing settings. Turning now to figure 3, a flexure assembly 10 suitable for use in camera 1 comprises a fixed portion 11 and a moving portion 12 operable to move along a movement axis M relative to the fixed portion 11. A pair of flexure elements 13 are fitted between the ends of the fixed and moving portions 11, 12. Each flexure element 25 13 is in the form of a flat shim having a central aperture 15. Optionally, each shim is provided with a stiffening element 16 in the form of a sheet bonded to the shim 14 by a number of rivets 17. This is illustrated most clearly in figure 4. The ends 141, 142 of each shim 14, adjacent to where the shims 14 are fitted to the fixed and moving portions 11, 12 are free to flex to enable movement of the moving 30 portion 12 relative to the fixed portion 11 along movement direction M. This flexure 26 08 25 assembly therefore deforms from a square or rectangular configuration defined between the shims 14 and fixed and moving portions 11, 12 to a parallelogram configuration. This movement for a single shim 14 is illustrated in figure 5. For a given range of movement AD along the movement direction M, there is a relatively small displacement 5 AH, the displacement AH determined by the length H of shim 14 and the permitted range of movement AD in the movement direction M. For example, a shim of length 48.6mm with a permitted displacement range of movement AD of = / -0.75mm would in experience a AH of 6pm. This is sufficiently small not to have an undue adverse impact on the operation of a camera 1 where displacement between lensing assembly 3 and 10 detector 2 is controlled by such a flexure arrangement 10. Turing to figures 6 and 7, these illustrate a camera 1 incorporating flexure assembly 10. The lensing assembly 3 is mounted to fixed portion 11 of flexure assembly 10. Typically, the lensing assembly 3 and / or fixed portion 11 would additional be mounted to a frame (not shown) or external housing (not shown) of the 15 camera 1. The detector 2, in the form of an imaging array, is mounted to the moving portion 12 of flexure assembly 10. As shown in the figures, the detector 2 may be provided with additional printed circuit boards 21-23 upon which additional components of the detector and / or control unit 5 may be provided. The detector 2 is 20 aligned with apertures 15 and the optical axis O of the lensing assembly 3. Linear actuator 4 is coupled to moving portion 12 and is operable to vary the displacement of moving portion 12 along movement axis M, which is aligned with optical axis O. A biasing spring 41 is provided to provide a biasing force acting against actuator 4. This can help restore the moving portion 12 to a desired origin position. 25 In this manner the flexure assembly 10, powered by the actuator 4 provides a lightweight mechanism that can facilitate ready control of the displacement between lensing assembly 3 and detector 2 and hence focussing of the camera 1. Furthermore, displacement perpendicular to the movement direction M / optical axis O is very low as discussed above. The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims. 26 08 25 26 08 25

Claims

1. A camera comprising: a detector operable to output a signal indicative of light incident upon the detector; a lensing assembly operable to direct incident light onto the detector, the lensing assembly having an optical axis aligned with the5 detector; and a flexure assembly operable to control variation of thedisplacement between the detector and the lensing arrangement along the said optical axis so as to vary camera focus; the flexure assembly comprising: a fixed portion; a moving portion spaced apart from the fixed portion; at least a pair of flexure elements spaced apart from one another and fitted between the fixed10 portion and moving portion, the at least a pair of flexure elements adapted topermit movement of the moving portion relative to the fixed portion along a movement axis and to resist movement of the moving portion relative to the fixed portion along axes other than the movement axis; wherein the detector is located between the fixed portion and the moving portion and between the pair15 of flexure elements.

2. A camera as claimed in claim 1 wherein the movement axis of the or each flexure element is aligned with the optical axis of the lensing assembly.

3. A camera as claimed in any preceding claim wherein the lensing assembly is mounted to the moving portion and the detector is mounted to the fixed portion.20 4. A camera as claimed in any preceding claim wherein the moving portion iscoupled to an actuator operable to move the moving portion relative to the fixed portion.

5. A camera as claimed in claim 4 wherein the actuator is controlled in response to a focus control system.25 6. A camera as claimed in any preceding claim wherein the moving portion isbiased in a particular direction or toward a particular position by the provision of one or more biasing elements.

7. A camera as claimed in any preceding claim wherein the flexure elements are rods or shaped blocks.26 08 258. A camera as claimed in any preceding claim wherein the flexure elements are flat shims.

9. A camera as claimed in claim 8 wherein each shim comprises a central aperture.

10. A camera as claimed in claim 8 or claim 9 wherein each shim is provided with5 a stiffening element.

11. A camera as claimed in any preceding claim wherein the flexure assembly comprises two flat shims, each flat shim fitted between corresponding ends of the fixed portion and the moving portion; and wherein each flat shim is provided with an aperture aligned with a common movement axis of the flat shims.10 12. A camera as claimed in claim 11 wherein the detector is provided between theflat shims and aligned with the optical axis.

13. A camera as claimed in claim 11 or claim 12 wherein the lensing assembly is provided at one end of the flexure assembly.

14. A camera as claimed in any preceding claim wherein the detector is operable to 15 detect light in the infrared (IR) wavelength range.

15. A camera as claimed in any preceding claim wherein the camera is a handheldcamera.

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