This application claims priority from United Kingdom Application for Patent No. 0919731.0 filed Nov. 11, 2009, the disclosure of which is hereby incorporated by reference.
The present invention relates to improvements in or relating to optical navigation devices, particularly but not exclusively in respect to miniature devices for use in a variety of different applications.
Current mobile or computer devices use a variety of different navigation mechanisms. Some of these present a mousing surface for direct manipulation by a finger (or other part of the body), and work by producing images of the finger as it moves on the mousing surface, translating this finger movement to movement of a cursor (for example) on a screen. In this respect a navigation device of this type works in a similar fashion to an optical mouse, and is referred to as an optical navigation device.
Most finger navigation devices use a mechanical push button system or a piezo-buffer sensor to detect pressure. These systems are expensive, not always reliable and take additional place into a navigation module.
Furthermore optical navigation devices such as those described above cannot detect pressure, requiring additional components for detection of additional actions. It is often desirable to obtain pressure information without adding any other components.
There is a need in the art to address one or more of the above issues.
In a first aspect of the invention there is provided an optical navigation device comprising: a radiation source capable of producing a beam of radiation; a sensor for receiving an image; and an optical element for identifying movement of an elastic object on a first surface to thereby enable a control action to be carried out, said first surface being such that a whole of the imaged area of said first surface is substantially covered by said elastic object in normal use; wherein said device further comprises means for determining the relative pressure applied to said first surface by said elastic object based upon the value of the average radiation intensity of said image received at the sensor.
The device may be operable such that pressure is a function of decreasing radiation intensity levels of said image received at the sensor.
Said optical navigation device may be operable to produce a stepwise pressure related output comprising of two or more states.
Said optical navigation device may be operable to mimic a push switch such that, should said optical parameter be on a first side of a predetermined threshold level then said device is operable to output a state mimicking a switch in its open state and should said optical parameter be on a second side of said predetermined threshold level then said device is operable to output a state mimicking a switch in its closed state. Ideally the side of the threshold level on which said device operates to output a state mimicking a switch in its closed state, is the side representative of a higher pressure being applied to said first surface.
There may be a plurality of threshold levels, wherein a different state is output depending on which threshold levels said value of said optical parameter falls between.
Said optical navigation device may be operable as an analog pressure sensor, by producing a linear pressure related output corresponding to said pressure applied to said first surface.
Said optical element may be operable to have the whole or a large part of said first surface substantially covered in normal use. In one embodiment, said elastic object is a finger, said first surface having an area of comparable size or smaller than that of an average fingertip. Said imaged area may be of the order of magnitude of 1 mm2.
Said navigation device may be packaged using Through Silicon Via technology. Said navigation device may be solderable using reflow solder techniques and therefore be able to withstand the high temperature of the reflow soldering process.
Said optical element may be formed from a single piece construction and may include at least one frustrated total internal reflection (F-TIR) surface capable of causing frustrated total internal reflection of the beam of radiation when said elastic object contacts said first surface to thereby generate the image which is capable of being translated into said control action. The optical element may comprise at least one further surface for directing radiation from the radiation source to at least one F-TIR surface. The optical element may comprise at least one additional surface for directing radiation from the F-TIR surface to the sensor.
The optical element may be formed from a plastics material, such as PMMA or polycarbonate.
In a further aspect of the invention there is provided a computer apparatus or a portable communications apparatus incorporating the navigation device herein described.
Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which:
The present invention relates to an optical navigation device module for use in a device. The device may be of any appropriate type and may include mobile phones, PDAs, Laptop computers, TV remotes, games controls and other such devices herein referred to as a computer application.
The optical navigation device module 100 includes a base plate 102, an optical element 106 which incorporates a clip 104 (the optical element will be described in greater detail below), an illumination source 108, such as an LED, and a sensor 110. The overall construction of the optical navigation device module 100 is of a low profile construction making it suitable for mobile devices. The actual size of the overall package containing the optical navigation device sits under a cap of about 7 mm in diameter and the module itself has a maximum dimension of about 5.8 mm.
The optical element 106 may be molded from a single piece of plastic and provides a so called mousing surface 112. An example of the type of plastic material is a monolithic optical block made of a plastics material such as poly (methyl methacrylate) also known as PMMA; although it will be appreciated other materials (such as Polycarbonate, Cyclophane copolymer) may alternatively be used.
As can be seen in
The F-TIR device 106 includes an LED 202 which emits a source of radiation directed by optical element 204 to the internal surface of the mousing surface 112. A further optical element 208 then directs any reflected radiation from the internal surface on to sensor 206.
The LED 202 may be of any appropriate type and may be mounted on a substrate. In a particular example the LED emits in the near infrared range for example between about 700 to 900 nm. It should be noted that the radiation emitted by the LED may be any appropriate wavelength. If the radiation is in the UV, optical or IR ranges the radiation may be referred to as illumination.
The optical element 204 directs the LED illumination into the monolithic optical block which forms the optical element 106. The optical element 204 may be in any appropriate to form for example a single convex surface; a series of lenslets configured as a “fly eye” structure; or any other suitable structure capable of providing near collimated illumination at the internal surface. The optical element 204 may be capable of being tilted in order to control the illumination pattern and direction of the beam at the mousing surface.
The mousing surface 112 includes an internal surface and an external surface. At the mousing surface any object with a refractive index which is placed in contact with the external surface will frustrate the total internal reflection of the beams 214 at the internal surface. A suitable object may include a finger, pointer, hand or other object or feature. A so-called frustrated reflection will thus be generated and the resulting pattern is focused by optical element 208 onto the sensor 206. The mousing surface 112 is designed here to be smaller than the object manipulating it such that the object covers most of all of the mousing surface, in use. In a main embodiment the surface is smaller in area than a fingertip, and is designed for finger manipulation.
The internal surface is relatively smooth when compared to the features which give rise to the F-TIR. Illumination reflected from the internal surface when there is no object close to the mousing surface is virtually 100% reflected. However, when the reflection is frustrated only about 10% or less of the illumination is reflected, thus resulting in contrast ratio of about 1:10 in the present example. Note that at 850 nm most of returned signal is from scattering at the object in contact with the optical element 106 (e.g. the skin of the user's finger).
The optical element 208 may be of any appropriate form, for example a single convex surface; and includes a stop (not shown) so that an image of F-TIR surface is produced at the sensor.
The frustrated reflection directed on to the sensor is detected in order to identify the point or points of contact of the object in contact with the external surface. Subsequent measurements of the point or points of contact will provide information corresponding to the movement of object on the external surface. The action or movement of the object can then be translated into actions to operate a mobile personal computer.
The system works at a frame rate of 1 to 10 kHz in order to detect relative movement or movements of one or more features at the F-TIR. The features detected at the F-TIR are features between about 0.5 mm and 30 μm in size and correspond, for example, to finger print features of a user. The smaller features provide a greater ability to detect motion than the larger ones. The sensor operates to determine motion vectors of one or more features from one frame to the next in accordance with the frame rate. Correlation from one frame to the next identifies the motion vectors and rate of movement which can then be translated into an appropriate control action for the mobile computer.
The frame rate is set by the refresh rate of the sensor. The exposure may be achieved by a pulsating illumination source (LED) or by sampling the sensor output at the required rate.
It may be possible to calibrate the sensor by determining the sensor illumination when there is no radiation source for F-TIR and comparing this with the sensor, when detecting F-TIR. This calibration may occur at the start of each use of the optical navigation device or on a frame to frame basis.
Such devices usually require a switch or selector to allow the user to select the object pointed to, for example the button(s) on a mouse. For a device as described, such a button may be provided separately. This is undesirable as it causes the device to be difficult to use, and requires extra space on the host device. Alternatively, the button can be incorporated into the function of the device, for example, by having the optical element movable vertically so as to operate a mechanical switching device, such as a bubble switch, under or incorporated into the device. The problems with this latter solution include the additional height required and the additional cost in providing the switch. Furthermore, such a device cannot determine differences in pressure, and are susceptible to reliability issues as a mechanical switch must eventually wear out with repeated use. Piezoelectric switches are another alternative, and can also be made to detect pressure, but are expensive and still require extra space.
To help address these issues, the inventor has determined that, when using an elastic material such as a finger to operate an optical navigation device and where the finger operates directly on the mousing surface, the harder that the mousing surface is pressed, the larger the deformation of the ridges of the fingerprints.
Such known systems are only really capable of measuring light pressure and no more, with there being no further increase in contact area between light pressure and relatively heavy pressure. Light pressure in this context would equate to a force in the region of 0.1N (equivalent to 500 Pa pressure for a 1 cm×2 cm finger). Normal mechanical switches require a typical activation force of 1N. Therefore such systems also could not be used effectively for mimicking push-button operation as described below.
The next row 330 shows the average intensity on the sensor, which in the first three examples is over a threshold, while in the last two examples, has fallen below this threshold. The final row 340 shows a “push button status”. This is explained below.
In a simplest application, this concept can be used to implement a push button functionality to an optical navigation device such as that described above. As can be seen in the last two rows 330, 340 of
A force in the region of 1N (equivalent to 5 kPa of pressure for 1 cm*2 cm finger) would be normally be enough to distort the ridges of most people and be detected by this method (greater pressure may be required for people with tougher skin, possibly 3N or more). This makes this method of pressure detection particularly suited to mimicking the actions of a push button, compared to the touchpad/touchscreen examples described above.
A navigation device which has a selection functionality without the need for a mechanical switch or piezoelectric element is therefore possible. Consequently, the navigation device can be made even smaller, without the need for vertical travel required for a conventional switch, and with a much simpler construction. Consequently such a device could be made reflowable (connectable through reflow soldering) using “Through Wafer Via” (TWV) integrated packaging techniques. Reflow soldering is a common process in the production of electronic devices. It consists in soldering all the components at the same time by heating these generally in an oven at around 260° C.
The threshold level could be adjusted to adapt the device to the user, depending on user's strength, fingerprint size, finger greasiness, skin color or other factors. However it might be possible to fix a threshold allowing any user to activate the pressure sensor without needing to press too hard on the navigation device.
Of course, it is easy to change such a threshold. Therefore it is simple to image several predefined set-ups to match with people who prefer a soft or a tough action on the navigation device.
It should also be noted that a device according to the invention, in an embodiment, can be used as an analog pressure sensor, instead of just a simple switch. There is good evidence that the pressure applied to the device is directly proportional to the average intensity measured. Therefore an average intensity scale can be set to determine pressure applied. This may find applications on 3-D mousing and navigation, or to control scrolling speeds, for example
Equally, instead of a linear scale, two or three thresholds may be set. One example of this may be to mimic a PC mouse, which conventionally has two buttons. In this embodiment there may be two thresholds, the device being operable such that pressure below a first threshold does not activate a button, but allows mousing (as before), a pressure between the two thresholds indicates the pressing of a first button, or a “soft press”, and a pressure over the second threshold indicates the pressing of a second button, or a “hard press”.
The above embodiments are for illustration only and other embodiments and variations are possible and envisaged without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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0919731.0 | Nov 2009 | GB | national |