The emergence of portable electronic computing platforms allows functions and services to be enjoyed wherever necessary. Palmtop computers, Personal Digital Assistants, mobile telephones, portable game consoles, biometric/health monitors, and digital cameras are some everyday examples of portable electronic computing platforms. The desire for portability has driven these computing platforms to become smaller and thus have a longer battery life.
It is difficult to efficiently collect user input on these ever-smaller devices. Portable electronic computing platforms need these user inputs for multiple purposes including, but not limited to, navigation: moving a cursor or a pointer to a certain location on a display; selection: choosing, or not choosing, an item or an action; and orientation: changing direction with or without visual feedback.
Prior art systems have borrowed concepts for user input from much larger personal computers. Micro joysticks, navigation bars, scroll wheels, touch pads, steering wheels and buttons have all been adopted, with limited success, in today's portable electronic computing platforms. All of these devices consume substantial amounts of valuable surface real estate on a portable device. Mechanical devices such as joysticks, navigation bars and scroll wheels can wear out and become unreliable. Because they are physically designed for a single task, they typically do not provide functions of other navigation devices. Their sizes and required movements often preclude optimal ergonomic placement on portable computing platforms. Moreover, these smaller versions of their popular personal computer counterparts usually do not offer accurate or high-resolution position information, since the movement information they sense is too coarsely grained.
A finger image sensor detects and measures features (e.g., valleys, ridges, and minutiae) on the surface of a finger through capacitive, thermal, optical, or other sensing technologies. Most commercially available finger image sensors fall into two categories: (1) full-size placement sensors and (2) typically smaller so-called swipe sensors. Placement sensors have an active sensing surface that is large enough to accommodate most of the interesting part of a finger at the same time. Generally, they are rectangular in shape with a sensing surface area of at least 100 mm2. The finger is held stationary while being imaged on the full-placement sensor.
The other type of finger image sensor, called a swipe sensor, is characterized by a strip-like imaging area that is fully sized in one direction (typically in length) but abbreviated in the other (typically width). An example is the Atrua Wings ATW100 sensor, as described by Andrade in US Patent Application 20030016849 and PCT patent application WO 02/095349. A finger is swiped across the sensor until all parts of it are imaged, analogous to how a feedthrough paper document scanner operates. A sequence of slices or frames of the finger image is captured and processed to construct a composite image of the finger.
Several prior art devices use a touchpad for authenticating a user and moving a cursor on a display device. A touchpad, which operates similarly to a finger image sensor, does not provide enough image resolution or capability to distinguish ridges and valleys on the fingerprint. Instead, the touchpad perceives a finger as a blob and tracks the blob location to determine movement. Therefore, a touchpad cannot follow miniscule movements, nor can it feasibly detect rotational movement.
U.S. Patent Publication No. 2002/0054695A1, titled “Configurable Multi-Function Touchpad Device,” to Bjorn et al. discloses a touchpad that can be configured to authenticate a user or to control a cursor. The touchpad attempts to enhance the function of a touchpad to include fingerprint capability. It merely absorbs the hardware of a capacitive finger image sensor into the much-larger size touchpad to achieve cost-savings. It does not disclose using the finger image data for navigation control. Undoubtedly, its large size still precludes the touchpad from being used in most portable electronic computing platforms.
U.S. Pat. No. 6,408,087, titled “Capacitive Semiconductor User Input Device,” to Kramer discloses a system that uses a fingerprint sensor to control a cursor on the display screen of a computer. The system controls the position of a pointer on a display according to detected motion of the ridges and pores of the fingerprint.
The system has a number of limitations. It uses image-based correlation algorithms and, unlike a system using a swipe sensor, requires fingerprint images with multiple ridges, typical for capacitive placement sensors. To detect a motion parallel to the direction of a ridge, the system requires the sensor to detect pores, a requirement restricting its use to high-resolution sensors of at least 500 dpi. The system detects changes in ridge width to sense changes of finger pressure. However, ridge width measurement requires a very high-resolution sensor to provide low-resolution of changes of finger pressure. The algorithm is unique to emulating a mouse and is not suitable for emulating other types of input devices, such as a joystick or a steering wheel, where screen movements are not always proportional to finger movements. For example, a joystick requires a returning to home position when there is no input and a steering wheel requires rotational movement. The system is unique to capacitive sensors where inverted amplifiers are associated with every sensor cell.