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 contact sensitive device comprising:
a member capable of supporting bending waves;
a plurality of sensors for measuring bending wave vibration in the member, wherein each of the sensors determines a measured bending wave signal; and
a processor responsive to the measured bending wave signals to calculate a location of a contact on the member, the processor 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 and utilized in determining the location of the contact, wherein the phase difference between the phase angles of each pair of sensors is given by
Δθ lm =θ 1 −θ m =k (ω 0 )Δ x lm +2π n 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, k(ω 0 ) is a wavevector and n lm is an integer.
2. A contact sensitive device according to claim 1 wherein the member is an input device for a graphical user interface and the processor is adapted to utilize information about expected contact location in calculation of the location of the contact.
3. A contact sensitive device according to claim 2 the graphical user interface presents a user with a choice of button locations to contact and the processor assumes that any contact on the member occurs within the button locations in determining the location of the contact.
4. A contact sensitive device according to claim 2 wherein probability of where a contact is likely to occur is utilized in determining the location of the contact.
5. A contact sensitive device according to claim 4 wherein the probability is based on one or more of location, size, and frequency of use of objects presented by the graphical user interface device.
6. A contact sensitive device according to claim 1 wherein sensors are piezoelectric vibration sensors.
7. A contact sensitive device according to claim 1 wherein a single value of the path length difference is determined for each pair of sensors and an intersection of two hyperbolae defined by the two path length differences defines the contact location.
8. A contact sensitive device according to claim 7 further comprising a plurality of band pass filters, and wherein the bending wave signal measured by each sensor is processed by two band-pass filters and two phase angles for each sensor are calculated and two phase angle differences are provided for each pair of sensors.