Contact sensitive device
A contact sensitive device includes a member capable of supporting bending waves and a plurality of sensors mounted on the member for measuring bending wave vibration in the member. The sensors measure the bending wave signals and by calculating a phase angle for each measured bending wave signal and a phase difference between the phase angles of at least two pairs of sensors so that at least two phase differences are calculated, the location of the contact can be determined.
1. A method of determining information relating to a contact on a contact sensitive device comprising:
providing a member capable of supporting bending waves and a plurality of sensors for measuring bending wave vibration in the member;
measuring a bending wave signal using each of the sensors in response to a contact being applied to the member at a location;
determining a phase angle for each measured bending wave signal;
calculating a phase difference between the phase angles of each sensor pair of at least two pairs of sensors; and
determining the location of the contact utilizing the at least two calculated phase differences.
2. A method according to claim 1 further comprising utilizing information about expected contact location in determining the location of the contact.
3. A method according to claim 2 where the member is a graphical user interface and presents a user with a choice of button locations to contact and the method further comprises assuming that any contact on the member occurs within the button locations in determining the location of the contact.
4. A method according to claim 2 further comprising utilizing probability of a contact occurring at a particular location in determining the location of the contact.
5. A method according to claim 4 wherein the probability of the contact occurring at the particular location is based on one or more of location, size, and frequency of use of objects presented by a graphical user interface.
6. A method according to claim 1 wherein the phase difference between the phase angles of each pair of sensors is given by Δθ lm =θ l −θ m =k(ω 0 )Δx lm +2πn lm where θ l and θ m are the phase angles of respective measured bending wave signals Δx lm=x l −x m is a path-length difference of two sensors, x l and x m being respective distances from the contact location to each sensor, kω 0 is a wavevector and n lm is an integer, and the method further comprises using a state-space estimator to evaluate the likelihood of successive sequences of n lm , and selecting one of the sequences having a maximum measure of likelihood.
7. A method according to claim 6 further comprising the state-space estimator utilizing a sequence of a pair of path-length differences taken at different times to estimate position and velocity of the contact at the different times.
8. A method according to claim 7 further comprising choosing a correct sequence of integers, n lm , for which the state-space estimator gives a maximum measure of likelihood.
9. A method according to claim 7 wherein the state-space estimator uses a random walk as a statistical description of motion of the contact.
10. A method according to claim 1 wherein determining the location of the contact is performed in a processor.
11. A method for determining a location of a contact on a member capable of supporting bending waves, the member having a plurality of sensors for measuring bending wave vibration in the member, the method comprising:
measuring bending wave signals at respective sensors in response to the contact being applied to the member at the location;
determining the location of the contact using at least one path-length difference for each sensor pair of at least two sensor pairs, the at least one path-length difference of each sensor pair being determined according to a phase angle difference of the bending wave signals measured by respective sensors of the sensor pair.
12. A method according to claim 11 wherein a single value of the path-length difference is determined for each sensor pair and an intersection of two hyperbolae defined by the at least two path-length differences defines the location of the contact.
13. A method according to claim 12 further comprising processing the bending wave signal measured by each sensor using separate band-pass filters, calculating two phase angles for the bending wave signal measured by each sensor, respective phase angles corresponding to each band-bass filter, and providing two phase angle differences for each sensor pair, the two phase angle differences for each sensor pair being used to calculate the single value of the path-length difference for each sensor pair.
14. A method according to claim 11 wherein determining the location of the contact is performed in a processor.