Method and apparatus for generating piezoelectric transducer excitation waveforms using a boost converter

• US 8,854,319 B1
• Filed: 01/07/2011
• Issued: 10/07/2014
• Est. Priority Date: 01/07/2011
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Nickson, Paul, Coleman, Lee, Umair, Muhammad, Alini, Roberto, Farooqui, Arshad Suhail
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): XAVIER, ANTONIO J
• Application Number:
  US12/986,905
• Time in Patent Office: 1,369 Days
• Field of Search: None
• US Class Current: 345/173
• CPC Class Codes: G06F 3/016 Input arrangements with force or tactile feedback as computer generated output to the user
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H03K 17/964 Piezoelectric touch switches

Abstract

Transducers formed as part of a touchscreen system emulate the motion of a pushbutton or other mechanical elements. A touchscreen system positions a transducer adjacent to an icon displayed on the touchscreen surface. When a user touches the icon, the transducer senses the touch and is then deformed in a pattern that emulates a mechanical motion, giving the user the sensation of touching a mechanical button. An excitation signal applied to the transducer is compared to a target excitation signal that, when applied to the transducer, causes the transducer to emulate the desired motion. When any differences between the two signals are detected, the excitation signal is adjusted so that the motion is corrected. The target excitation signal, or time and voltage segments defining it, are stored in memory and retrieved for comparison. The excitation signal is also selected to reduce any acoustic artifacts that can cause the transducer to generate audible clicks.

Claims

1. A system for deforming a material comprising:

a deformable material; and

control logic configured to dynamically adjust a peak charging current to adjust an energy transfer rate of a DC-to-DC step up converter, the DC-to-DC step up converter applies, according to a predetermined pattern, a controlled charge to the deformable material and provides an increasing energy transfer rate to reduce a voltage step size to adjust a waveform according to the predetermined pattern.

2. The system of claim 1, further comprising a feedback loop to monitor and adjust the peak charging current.

3. The system of claim 2, wherein the feedback loop comprises a fly-back boost converter.

4. The system of claim 1, further comprising a discharge current path coupled in parallel to the deformable material, the control logic is configured to dynamically adjust a discharge current.

5. The system of claim 2, further comprising a memory storing one or more digital representations of excitation waveforms for deforming the deformable material according to the predetermined pattern.

6. The system of claim 5, wherein the digital representations are a sequence of voltage and time segments to control a step size.

7. The system of claim 1, wherein the deformable material forms part of a touch sensing element that when contacted triggers signals to deform the deformable material.

8. The system of claim 1, wherein the deformable material comprises a transducer.

9. The system of claim 8, wherein the transducer is an electro-mechanical vibration transducer.

10. The system of claim 9, wherein the electro-mechanical vibration transducer is a linear resonance actuator transducer.

11. The system of claim 1, further comprising a liquid crystal display displaying icons such that the predetermined pattern is sensed at the icons.

12. A touchscreen device comprising:

a liquid crystal display for displaying one or more icons;

a touch sensing element configured to sense a touch thereon and, in response, to move according to a predetermined pattern, the movement transmitted to at least one of the one or more icons;

a fly-back boost converter using peak primary charging currents to generate voltages applied to the touch sensing element, wherein the peak primary charging currents are dynamically adjusted to provide an energy transfer rate that reduces a voltage step size to adjust a waveform according to a target pattern; and

a memory coupled to the fly-back boost converter, the memory storing digital representations of voltages used to drive the fly-back boost converter.

13. The touchscreen device of claim 12, wherein the touch sensing element comprises one or more transducers.

14. The device of claim 12, wherein the digital representations are stored as one of segments and splines.

15. The device of claim 14, further comprising a control logic that dynamically interpolates between segments by adjusting the charging and discharging parameters to determine actual points on the waveform.

16. The device of claim 15, wherein the control logic is configured to select one of a plurality of waveform signals in response to determining an undershoot in the waveform signal.

17. The device of claim 14, wherein the digital representations comprise coordinates of time and voltage to control the voltage step size.

18. The device of claim 14, wherein the digital representations are compressed to conserve memory.

19. The device of claim 16, wherein the peak primary charging current reduces an initial energy transfer to increase a charge rate at high voltages.

20. The device of claim 19, wherein the peak primary charging current increases the initial energy transfer in response to determining the undershoot in the waveform signal.