Patent Application
20110200314
The present convention relates generally to auto focus imaging systems, and more particularly, to imaging systems capable of reading effectively over a wide range distances from a near field to a far field. Such devices may also be used to capture images of symbols to be decoded, or as general imaging devices for capture of any type of image. When used to read and decode data symbols, these devices may be called code scanners, even though they are not “scanners” in the sense of more conventional laser scanners.
Imaging devices using liquid lenses have recently been introduced. Such liquid lens systems use a voltage that is applied to fluids, which voltage alters the shape of the surface of the fluids, creating lenses of varying properties. By varying the applied voltages correctly, the optical properties of the lens can be set as required in any particular application.
In accordance with one aspect of the present invention, a code scanner, which illuminates a scanned code from a distance, includes a liquid lens that focuses the reflected image of the code on an image sensor. The scanner includes a range detector, preferably laser-based, which determines the distance to the scanned code, and the liquid lens is controlled to focus at the detected distance. The presence of a range detector is itself optional, and not critical to the present invention.
In accordance with an enhanced embodiment, the system includes a temperature sensor located proximate to the liquid lens. The temperature sensor is operable with a storage means that includes previously derived data indicating the length of time the lens will take to properly respond to—i.e; alter its properties in response to—an applied voltage. As these properties vary with temperature, the use of the previously derived data allows the system, after applying the proper voltage to the liquid lens, to wait the least amount of time possible before capturing the desired image.
The foregoing brief description, and other objects, features and advantages of the present invention will be understood more completely from the following detailed description of presently preferred, but nonetheless illustrative, embodiments in accordance with the present invention, with reference being had to the accompanying drawings, in which:
Turning now to the details of the drawings,
A liquid lens 18 is interposed in the light path L between bar code 14 and image sensor 16. Those skilled in the art will understand that this is an electro optical type of device which has a optical interface between two transparent layers. Through the adjustment of an applied voltage, the shape of that interface maybe changed, changing the focal length of the lens. The distance between the lens 18 and image sensor 16 remains fixed, however, the distance to the left of lens 18 of the plain on which the lens will focus will vary with the applied voltage. It is therefore possible to focus barcodes 14 at a range of distances from image sensors 16 by simply varying a voltage that controller 20 applies to lens 18. Mechanical movement of the lens is not necessary. However, it will be appreciated that the control voltage applied to lens 18 must be correlated to the actual distance of barcode 14 from lens 18 and, therefore, from image sensor 16.
In order to ensure appropriate control of lens 18, a ranging apparatus is provided which preferably comprises a laser device and a laser detector 24. Two types of laser ranging technology are well known in the art. Pulsing technology measures the delay time between the initiation of a laser pulse and the return of its reflection. Parallax technology projects a light beam to form a spot on a target and then measures the position of the detected spot on the target. The distance of the target can be determined from the position of the detected spot. Preferably, laser device 22 and detector 24 define a parallax ranging subsystem. Laser 22 projects a light beam onto bar code 14 and detector 24 senses the position of the resulting dot and determines the distances of bar code 14. It then produces a signal representative of that distance, which is applied to controller 20. In response, controller 20 is then able to apply a voltage to lens 18 to focus it appropriately.
The output signal of detector 24 is also applied to light source 12, the intensity of which is controlled accordingly. In its simplest form, source 12 could be a ray of light emitting diodes, and the intensity could be controlled by the numbers of diodes on the array that are turned on (more simply by changing optical output power). The intensity of light source 12 could also be controlled by varying the dispersion angle of the light at the midst. Those skilled in the art will appreciate that that could be achieved mechanically by controlling the angle of vain-like devices or the like, or it can be achieved optically with a condensing lens. It would be possible to provide a plurality of condensing lens and select among them or to provide a zooming lens, possibly even a liquid lens.
In any event, through the controller focus distance and light source illumination in relationship to the distance of the bar code, it becomes possible to achieve DOF performance which approaches the ideal.
Preferably, liquid lens 18 is ARCTIC-414 or ARCTIC-416 produced by Varioptic. However, other liquid lenses may be utilized as well.
In a preferred arrangement, the laser is mounted atop of the camera module, instead of at the sides or on the bottom. Additionally, the laser should be offset from the optical axis by an amount equal to 6-15 mm. Moreover, if a LEDs are used for illumination, they should be mounted on the opposite of the module from the laser, in order to minimize the effects of reflection.
As indicated previously the present invention exhibits advantages over the prior art in that it is capable of focusing a code image more quickly, in that it avoids the use of moving parts, eliminating the associated reliability issues; in that it has a substantially greater focus range; and in that it is easily retrofitted into existing scanning systems
Since differing temperatures mandate differing wait times, the temperature value may be updated as the device operates. In a preferred embodiment, the controller is programmed to required a temperature update periodically. Alternatively the update can be provided whenever the temperature sensor detects a change in temperature my more than a prescribed amount.
While the foregoing describes the preferred embodiment of the invention, various other modifications and additions will be apparent to those of skill in the art. Such modifications and additions are intended to be covered by the claims appended hereto.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/72876 | 8/12/2008 | WO | 00 | 3/24/2011 |
