阅读说明：本技术 压电用户接口装置和用于驱动用户接口装置中压电元件的方法 (Piezoelectric user interface device and method for driving piezoelectric element in user interface device ) 是由 戴维德·拉克鲁斯 图罗·赫尔曼尼·凯斯基·贾斯卡里 于 2020-03-31 设计创作，主要内容包括：压电用户接口装置包括电压转换器(103),用于可控地产生驱动一个或更多个压电元件(101)的电压波形。电压转换器(103)具有控制输入(201)。控制器(105)耦接(202)到所述控制输入(201)以控制所述电压转换器(103)的输出电压。控制器(105)具有一个或更多个缩放输入(203、204、205、208)。控制器(105)形成所述控制信号以使所述输出电压作为时间的函数跟随目标波形(301)。控制器(105)被配置为基于通过所述一个或更多个缩放输入(203、204、205、208)接收的缩放信息缩放所述目标波形。(The piezoelectric user interface device comprises a voltage converter (103) for controllably generating a voltage waveform for driving one or more piezoelectric elements (101). The voltage converter (103) has a control input (201). A controller (105) is coupled (202) to the control input (201) to control the output voltage of the voltage converter (103). The controller (105) has one or more scaling inputs (203, 204, 205, 208). The controller (105) forms the control signal to cause the output voltage to follow a target waveform (301) as a function of time. The controller (105) is configured to scale the target waveform based on scaling information received through the one or more scaling inputs (203, 204, 205, 208).)

1. A piezoelectric user interface device, comprising:

-a voltage converter (103) configured to controllably generate a voltage waveform for driving one or more piezoelectric elements (101), the voltage converter (103) having at least one control input (201, 206), and

-a controller (105) coupled (202) to the at least one control input (201, 206) and configured to control an output voltage of the voltage converter (103) by applying a control signal to the at least one control input (201, 206), the controller (105) having one or more scaling inputs (203, 204, 205);

wherein the controller (105) is configured to form the control signal such that the output voltage follows a target waveform (301) as a function of time, and

wherein the controller (105) is configured to scale the target waveform based on scaling information received through the one or more scaling inputs (203, 204, 205, 208).

2. The piezoelectric user interface device according to claim 1, wherein the controller (105) is configured to scale (503, 507, 702, 706) the amplitude of the target waveform based on the scaling information.

3. The piezoelectric user interface device according to claim 1 or 2, wherein the controller (105) is configured to scale (703, 707) a length of time of the target waveform based on the scaling information.

4. The piezoelectric user interface device according to any one of the preceding claims, wherein the zoom input (203, 204, 205, 208) comprises a configuration input (203) for pre-receiving at least part of the zoom information as configuration information.

5. The piezoelectric user interface device according to any one of the preceding claims, wherein the scaling input (203, 204, 205, 208) comprises a feedback input (204, 205) for dynamically receiving at least part of the scaling information as feedback information during generation of a voltage waveform.

6. The piezoelectric user interface device according to claim 5, wherein the feedback input (204, 205) comprises a voltage feedback input (204) for receiving feedback of the output voltage.

7. The piezoelectric user interface device according to claim 5 or 6, wherein the feedback input (204, 205) comprises a current feedback input (205) for receiving feedback of the output current of the voltage converter (103).

8. The piezoelectric user interface device according to any one of the preceding claims, wherein the zoom input (203, 204, 205, 208) comprises an internal input (208) for using an internal quantity of a controller (105) as the zoom information.

9. A piezoelectric user interface device as in any one of the preceding claims, wherein:

-the voltage converter (103) comprises a boost converter comprising a power switch (212) for closing and opening a current path through a boost inductor (211),

-the control signal comprises switching pulses to the power switch (212), and

-the controller (105) is configured to vary at least one of a duty cycle and a switching frequency of the switching pulses to control the output voltage.

10. A method for driving a piezoelectric element in a user interface device, the method comprising:

-controllably generating (901) a voltage waveform for driving one or more piezoelectric elements,

-controlling (903) the generation of the voltage waveform such that the generated voltage waveform follows a target waveform as a function of time, and

-scaling (904, 1001) the target waveform based on the received scaling information.

11. The method as recited in claim 10, wherein the scaling (904, 1001) of the target waveform includes scaling at least one of an amplitude and a length of time of the target waveform.

12. The method according to any one of claims 10 or 11, comprising:

-receiving in advance at least part of the scaling information as configuration information or as stored information indicating an effective measure for generating a voltage waveform found during one or more previous generation attempts.

13. The method of any of claims 10 to 12, comprising:

-dynamically receiving at least part of the scaling information as feedback information during generation of the voltage waveform.

14. The method of claim 13, wherein the feedback information comprises voltage feedback from the generation of the voltage waveform.

15. A method according to claim 13 or 14, wherein the feedback information comprises current feedback for delivering the output current of the voltage waveform.

16. The method of any one of claims 10 to 15, wherein:

a voltage converter for generating the voltage waveform,

-giving a control signal as a switching pulse to a power switch in the voltage converter, and

-the method comprises varying at least one of a duty cycle and a switching frequency of the switching pulses such that the output voltage of the voltage converter follows the target waveform as a function of time.

Technical Field

The present invention relates to techniques for generating haptic effects in electromechanical user interface devices. In particular, the invention relates to the task of ensuring a satisfactory and consistent user experience, regardless of the number of piezoelectric elements to be driven, and regardless of other factors such as manufacturing tolerances of the piezoelectric elements, varying environmental conditions such as temperature, etc.

Background

Piezoelectric elements are commonly used to generate haptic effects in input devices such as touch keys, touch screens, etc., i.e., to reproduce a sense of touch by applying force, vibration, or motion to a user. The piezoelectric element may be used to sense the force applied by the user and generate haptic feedback. The first mentioned involves sensing the voltage generated by the piezoelectric element in response to mechanical deformation, while the latter involves applying a voltage waveform to the piezoelectric element causing it to temporarily mechanically deform, thereby inducing a corresponding elastic motion in the surrounding structure.

For the task of applying a voltage waveform to the piezoelectric element, a driver circuit is used. Fig. 1 schematically shows a combination of a piezoelectric element 101 and a driver circuit. The voltage source 102 supplies an input voltage to the voltage converter 103, the task of which is to generate a voltage waveform. The output filter 104 is shown separately here, although it may be considered as part of the voltage converter 103. The control circuit 105 controls the operation of the other modules; it may receive feedback measurements from them and issue control commands to them.

The amplitude of the voltage waveform required to drive the piezoelectric element 101 may be relatively high, on the order of hundreds of volts, while the voltage provided by the voltage source 102 is typically much lower, for example on the order of only a few volts, or on the order of ten or twenty volts. Therefore, the voltage converter 103 must include a boost capability to controllably bring the output voltage to the full amplitude of the voltage waveform and back. The duration of the voltage waveform is typically measured in units of milliseconds or tens of milliseconds. The waveform may be a single polarity voltage pulse or it may contain one or more negative polarity half-waves and one or more positive polarity half-waves, so the amplitude here is the absolute value of the amplitude. Suitable control signals from the control circuit 105 may be used to cause the voltage converter 103 to generate the voltage waveform accurately at the desired amplitude and form.

It has been found that the form of the voltage pulse has a significant impact on the user experience, not only with respect to the user's touch sensation, but also with respect to the user's listening sensation. In particular, the first and higher order time derivatives of the voltage, i.e. the rate of change of the voltage at each part of the voltage waveform, are important. As a basic rule, keeping the first time derivative of the voltage small enough suppresses audible artifacts, which are undesirable in many application scenarios. In other cases, it may be possible to target some audible sound, meaning that the voltage waveform is intentionally designed to contain sufficiently fast changes.

However, problems may arise if the same driver circuit should be used to drive multiple piezoelectric elements simultaneously, and/or if changes in temperature or other environmental conditions change the mechanical response of the structure affected by the piezoelectric elements. For example, manufacturers of piezoelectric input devices may provide products to automobile manufacturers that wish to use the products in various portions of the automobile instrument panel. In some portions of the instrument panel, the driver circuit has only one piezoelectric element to be driven, while in some other portions, four or more piezoelectric elements are simultaneously driven by a single driver circuit. The large load presented by the multiple piezoelectric elements may exceed the output capability of the driver circuit. As a result, the voltage waveform may be distorted, with the adverse consequence that the user experience is not desirable.

A brute-force solution to this problem is to always equip each piezoelectric element with its own driver circuit, but this is a costly solution in terms of component cost and required installation space. Another brute-force solution is to design the driver circuit to have sufficient power to drive the maximum number of piezoelectric elements that will be encountered. This would also be expensive, since in most cases the size of the driver circuit would be too large. Another solution is to provide a set of driver circuits of different sizes, but this can involve significant problems in the logistics and management of product combinations.

Disclosure of Invention

It is an object of the present invention to provide a piezoelectric user interface device which is flexibly adapted to drive a piezoelectric element under various conditions without having to over-adjust the dimensions of its components.

This and other advantageous objects are achieved by using a controller that can scale a target waveform based on scaling information that may be obtained in advance and/or dynamically during generation of a voltage waveform.

According to a first aspect, a piezoelectric user interface device is provided. It comprises a voltage converter configured to controllably generate a voltage waveform for driving one or more piezoelectric elements. The voltage converter has a control input. The piezoelectric user interface device comprises a controller coupled to the control input and configured to control the output voltage of the voltage converter by applying a control signal to the control input. A controller has one or more scaling inputs and is configured to form the control signal to cause the output voltage to follow a target waveform as a function of time. The controller is configured to scale the target waveform based on scaling information received through one or more scaling inputs thereof.

According to an embodiment, the controller is configured to scale the amplitude of the target waveform based on the scaling information. This involves the advantage that the generation of the voltage waveform can often be more successful if one does not try to generate such high voltages, which in some cases proves difficult or impossible.

According to an embodiment, the controller is configured to scale the length of time of the target waveform based on the scaling information. This involves the advantage that the time derivative characteristic of the voltage waveform can be controlled more accurately.

According to an embodiment, the zoom input comprises a configuration input for receiving at least part of the zoom information as configuration information in advance. This involves the advantage that the operation of the piezo user interface device can be actively adapted to different conditions.

According to an embodiment, the scaling input comprises a feedback input for dynamically receiving at least part of said scaling information as feedback information during generation of the voltage waveform. This involves the advantage that the operation of the piezo user interface device can be flexibly adapted to conditions that cannot even be considered in advance.

According to an embodiment, the feedback input comprises a voltage feedback input for receiving feedback of the output voltage. This involves the advantage that an accurate and reliable feedback can be obtained with a relatively simple circuit.

According to an embodiment, the feedback input comprises a current feedback input for receiving a feedback of the output current of the voltage converter. This involves the advantage that the feedback can be made to indicate the actual output power.

According to an embodiment, the scaling input comprises an internal input for using an amount internal to the controller as said scaling information. This involves the advantage that scaling can be performed entirely within the controller circuitry, preferably using programmable means.

According to an embodiment, a voltage converter includes a boost converter including a power switch for closing and opening a current path through a boost inductor; the control signal is a switching pulse to the power switch; and the controller is configured to vary at least one of a duty cycle and a switching frequency of the switching pulse to control the output voltage. This involves the advantage that even relatively high output voltages can be generated and controlled in a well-known and stable manner.

According to a second aspect, a method for driving a piezoelectric element in a user interface device is provided. The method comprises controllably generating a voltage waveform for driving one or more piezoelectric elements, controlling the generation of the voltage waveform such that the generated voltage waveform follows a target waveform as a function of time, and scaling the target waveform information based on received scaling information.

According to an embodiment, the scaling of the target waveform comprises scaling at least one of an amplitude and a length of time of the target waveform. This involves the advantage that the generation of the voltage waveform can often be more successful and the time derivative characteristics of the voltage waveform can be more accurately controlled without attempting to generate such high voltages, which in some cases may prove difficult or impossible.

According to an embodiment, at least part of the scaling information is received as configuration information in advance. This involves the advantage that the operation of the piezo user interface device can be actively adapted to different conditions.

According to an embodiment, the method comprises dynamically receiving at least part of the scaling information as feedback information during the generating of the voltage waveform. This involves the advantage that the operation of the piezo user interface device can be flexibly adapted to conditions that cannot even be considered in advance.

According to an embodiment, the feedback information comprises voltage feedback from the generated piezoelectric waveform. This involves the advantage that an accurate and reliable feedback can be obtained using relatively simple circuitry.

According to an embodiment, the feedback information comprises a current feedback for delivering the output current of the voltage waveform. This involves the advantage that the feedback can be made to indicate the actual output power.

According to an embodiment, a voltage converter is used to generate the voltage waveform, a control signal is given as switching pulses to power switches in the voltage converter, and the method comprises varying at least one of a duty cycle and a switching frequency of the switching pulses such that the output voltage of the voltage converter follows the target waveform as a function of time. This involves the advantage that even relatively high output voltages can be generated and controlled in a well-known and stable manner.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the figure:

figure 1 shows a piezo-electric user interface device,

figure 2 shows an exemplary embodiment of a piezo user interface device,

figure 3 shows an example of a target waveform,

figure 4 shows an example of pre-scaling a target waveform based on configuration information,

figure 5 shows an example of dynamically scaling a target waveform based on feedback information,

figure 6 shows an example of pre-scaling a target waveform based on configuration information,

figure 7 shows an example of dynamically scaling a target waveform based on feedback information,

figure 8 shows an example of pre-scaling a target waveform based on configuration information,

FIG. 9 shows an example of a method, and

fig. 10 shows an example of a method.

Detailed Description

Fig. 1 and 2 are compared with each other. Fig. 2 shows an example of how the principle of fig. 1 can be implemented in practice. As with previous electronic circuits, it should be noted that the example of fig. 2 illustrates only one implementation among many possible implementations. It will be clear to a person skilled in the art that there are many other possible embodiments from the following description of how the various parts of the device are intended to operate and interact with each other.

The piezoelectric user interface device as illustrated in fig. 1 and 2 comprises a voltage converter 103 configured to controllably generate a voltage waveform for driving the one or more piezoelectric elements 101. The voltage converter 103 has a control input 201. In the example of fig. 2, the voltage converter 103 has the topology of an inductive boost converter, wherein a current loop from the positive node of the voltage source 102 through the boost inductor 211 to the negative node of the voltage source 102 may be formed by closing the power switch 212. A diode 213 is coupled from a point between the boost inductor 211 and the power switch 212 in the forward direction to one output node of the voltage converter 103, and the negative node coupled to the voltage source 102 constitutes the other output node.

Control input 201 controls the conductive state of power switch 212. The repeated switching pulses for the control input 201 cause the power switch 212 to alternate between a conductive state and a non-conductive state, which causes an output voltage to appear at the output of the voltage converter 103. A capacitor is used as the output filter 104 to smooth the output voltage. The boost topology means that the output voltage may be higher than the voltage available at the voltage source 102. Changing the frequency and/or pulse width of the switching pulses causes the output voltage to change. A practical voltage converter with a boost topology may include many other components and this simplified example is used here only for clarity of the drawing and ease of understanding.

The use of switching pulses to the power switch 212 as a control signal and a switching control line as in fig. 2 as a control input 201 is also merely an example. Known techniques of controlling the output voltage of a voltage converter provide many alternatives, such as using a dedicated switch driver circuit as part of the voltage converter and giving control signals to the switch driver circuit in the form of voltage levels or the like. For the purposes of this description, it is sufficient to assume that there is a clear relationship between the control signal and the output voltage of the voltage converter 103, and that this relationship can be used to drive a sufficiently high output voltage and to change the output voltage in a sufficiently fast and controlled manner for driving the one or more piezoelectric elements 101.

The boost topology is an advantageous choice for the voltage converter 103 because it can produce an output voltage that is significantly higher than the input voltage, its operating characteristics are well known, and its operating stability is good. Other converter topologies may be used, such as the known SEPIC, buck-boost, flyback, half-bridge, full-bridge, forward or split pi topologies, or capacitive charge pumps. If a sufficiently high input voltage is available, the voltage converter may have a topology that does not produce an output voltage higher than the input voltage, such as a buck topology. The basic converter topology may add additional circuitry (e.g., a voltage doubler) at its output to bring the maximum available output voltage to the desired level.

The piezoelectric user interface device as shown in fig. 1 and 2 comprises a controller 105 coupled to a control input 201 of the voltage converter 103. Fig. 2 illustrates the coupling such that there is a control signal output 202 in the controller 105 and a coupling (C-C) exists between the control signal output 202 and the control input 201. The controller 105 is configured to control the output voltage of the voltage converter 103 by applying a control signal to the control input 201. Some examples of control signals have been discussed above; in the simplified example of fig. 2, the controller 202 will generate a switching pulse that will be conducted to the control input 201 to control the conductive state of the power switch 212. In this case, the controller 105 is configured to change the duty ratio and/or the switching frequency of the switching pulses for controlling the output voltage of the voltage converter 103. The controller 105 further comprises one or more so-called scaling inputs 203, 204 and 205, the significance and use of which will be described in more detail later herein.

The other part of fig. 2 schematically shows a controllable discharge connection comprising a discharge switch 216 and a discharge resistor 217 coupled in series across the output of the voltage converter 103. The controller 105 has an additional control signal output 207 for controllably rendering the discharge switch 216 conductive or non-conductive. The controller 105 may use a controllable discharge connection to discharge power from the output of the voltage converter 103, which may help shape the output voltage waveform of the voltage converter 103, particularly in its reduced portion. A more versatile form of controllable discharge connection may be provided, for example by using semiconductor switches that can be driven in their linear region, and/or by using a plurality of different, individually controllable current paths.

The controller 105 may be or include a microprocessor, microcontroller, control computer, or other kind of programmable device that can be programmed to operate in a desired manner, i.e., to cause execution of one or more sets of machine-readable instructions stored on a machine-readable medium. The controller 105 may include an internal program memory for storing such instructions, and/or it may read such instructions from one or more external storage devices. Another possibility is to use a fixed-function state machine, which is not strictly programmable. The controller 105 may be a dedicated controller for the piezoelectric user interface device, or it may be a larger physical controller, such that only part of its task employs the piezoelectric user interface device. The controller 105 may include and implement functionality that is at least partially distributed among several physical entities, such as a high-level control computer responsible for the operation of the larger entities and low-level control circuitry that interacts only with other portions of the piezoelectric user interface device under the control and supervision of the high-level control computer.

The controller 105 is configured to form the control signal in such a way that the output voltage of the voltage converter 103 follows the target waveform as a function of time. This is possible when the operating characteristics of the voltage converter 103 are well understood. For example, for an ideal voltage converter with a boost topology, the output voltage can be calculated from the input voltage and the duty cycle of the switching pulses in a known manner. Assuming that the input voltage remains constant, the controller 105 may cause the output voltage to follow the target waveform by applying a switching pulse with a correspondingly varying duty cycle D to the control input 201. Known deviations from ideal operation can be accounted for by way of compensating modifications to the generated switching pulses.

The target waveform may be considered to be a voltage-time plot that has been stored in memory available to the controller 105 and is expected to follow the output voltage of the voltage converter 103. When a trigger input occurs, such as a processor interrupt, which requires the user to be given a tactile feedback using the piezoelectric element, the controller 105 reacts by outputting a corresponding control signal during a time interval corresponding to the length of time that a tactile feedback is to be given. The present invention extends the concept of a target waveform to a target waveform that is calculated on-the-fly during generation of the voltage waveform, as will be explained in more detail later herein.

As previously indicated herein, in some cases, if the controller 105 merely follows the previously stored target waveform when it is giving the control signal, the final output voltage will not actually behave according to the target waveform. The reason for this may be, for example, that so many piezoelectric elements 101 have been coupled in parallel that the load capacitances they represent together become too large for the voltage converter 103 to handle properly. Another possible reason is that the temperature of the piezoelectric element is so different from the default temperature that the mechanical properties of the piezoelectric element are so far different from what it is expected. An output voltage waveform that deviates from the target waveform may cause undesirable effects such as unwanted noise and/or unstable types of elastic deformation in the piezoelectric element 101.

Voltage feedback from the output of the voltage converter 103 to the input of the controller 105 may be used to some extent to counteract the tendency of the output voltage to deviate from the target waveform. However, voltage feedback only works if there is sufficient spare capacity available in the voltage converter 103, but this is not always the case.

To provide better adaptability in the event that the original target waveform cannot be followed, the controller 105 is configured to scale the target waveform based on scaling information received through one or more scaling inputs 203, 204 or 205. The kind of scaling information that may be received, where this scaling information may originate from, and how the scaling of the target waveform is actually achieved, will be described below.

Fig. 3-5 relate to examples in which the controller 105 is configured to scale the amplitude of the target waveform based on the scaling information. An example of the original form of the target waveform is shown as voltage-time plot 301 of fig. 3. For clarity of the drawing and ease of understanding, the target waveform shown here includes only a single positive half-wave. This should not be construed as limiting: the same considerations apply regardless of the polarity and/or complexity of the target waveform.

One example of the zoom input of the controller 105 is a configuration input by which the controller 105 can receive at least part of the zoom information as the configuration information in advance. In other words, the controller 105 may receive information regarding a non-default configuration of the piezoelectric user interface device from some external source. The default configuration may be, for example, a configuration in which the piezoelectric user interface includes N1 piezoelectric elements, where N1 is a positive integer (N ═ 1, 2, 3, … …). The left-most target waveform in fig. 4 shows how the original target waveform 301 would be applied unchanged when the number of piezoelectric elements to be driven is N1. The configuration information indicating that the number of piezoelectric elements is N2 or N3 makes the amplitude of the scaled target waveform of the controller 105 smaller, where N2 and N3 are positive integers and N1< N2< N3, as shown in the middle and right scaled target waveforms 401 and 402 in fig. 4.

The configuration information may be related to other factors in addition to (or instead of) the number of piezoelectric elements to be driven. For example, in an automobile or other mounted instrument panel that may be used under widely varying environmental conditions, the configuration information may include an indicator that affects the temperature of the piezoelectric element. In general, i.e. before the actual generation of the output voltage from the (scaled) target waveform, the configuration information comprises all information that may be provided to the controller 105 in advance. It also contains information that the controller 105 and/or some closely related circuitry can autonomously generate in advance, such as self-measured temperature and/or capacitance of the load, and/or accumulated information about how the load is as a function of temperature.

In addition to (or as an alternative to) the configuration information, the scaling information may comprise feedback information obtained dynamically during generation of the voltage waveform. The schematic shown in fig. 2 illustrates two examples of devices that can be used dynamically to obtain feedback in real-time: a voltage detection circuit 214 and a current detection circuit 215. In such operation, the feedback information is thus not (only) used to cause the voltage converter 103 to follow the previously stored target waveform more closely, but the target waveform itself is changed. Feedback information may also be obtained from other measured quantities, such as the effort required to cause the generated waveform to follow the target waveform. As in the example illustrated in fig. 5.

The leftmost portion of fig. 5 illustrates how the original target waveform 301 remains the waveform to be targeted when the piezoelectric user interface device begins to generate a particular instance of haptic feedback to the user. Although not mandatory, it is possible to initially apply voltage feedback in an attempt to ensure that the actual output voltage of the voltage converter 103 follows the target waveform. However, at the time shown as 501, rather early relative to the total length of time of the target waveform, the feedback information indicates that there is a gap 502 between the currently valid target waveform 301 and the actually achieved output voltage (the development of which is represented by the solid line in fig. 5). This feedback information causes the controller 105 to scale the amplitude of the target waveform lower as illustrated with arrow 503 so that the new target waveform is the scaled target waveform 504 in the middle portion of fig. 5.

One of the other examples mentioned above, i.e. obtaining feedback from what seems to be needed effort, may for example work in the following way. The controller knows what duty cycle should be sufficient for the generated voltage waveform to follow the target waveform at time 501. However, voltage feedback has resulted in the use of duty cycles that are larger than expected. In other words, the fact that there is no gap 502 at time 501, but a higher effort than expected, may occur, indicating that a gap may develop later, even if the peak of the target waveform has not been reached, a time at which the voltage feedback can no longer increase the duty cycle may occur.

The controller may perform the checking of the actual duty cycle and its comparison with the expected duty cycle internally. Thus, the concept of a "scaling input" of the controller may be generalized to also cover internal inputs, e.g. internal inputs that feed the actual duty cycle to the evaluation and comparison with the expected duty cycle. The internal input may use an internal quantity of the controller as the scaling information. This internal input may be achieved by appropriate programming in the instructions executed by the controller. To this end, an internal scaling input 208 is schematically illustrated in FIG. 2.

Regardless of what scaling was actually triggered at time 501, the current instance of generating haptic feedback to the user continues. If voltage feedback control is in use, an effort may be made to ensure that the actual output voltage of the voltage converter 103 follows the new, scaled target waveform 504. However, it is assumed in fig. 5 that at a time 505, which is still very early with respect to the total time length of the target waveform, the feedback information indicates that there is still a gap 506 between the currently valid target waveform 504 and the actually achieved output voltage. This feedback information causes the controller 105 to scale the amplitude of the target waveform lower as illustrated by arrow 507 so that the new target waveform is the scaled target waveform 508 in the rightmost portion of fig. 5.

In fig. 5, it is assumed that after the second scaling is demonstrated with arrow 507, the continuously obtained voltage feedback information demonstrates that the actual output voltage of the voltage converter 103 follows the latest, twice scaled target waveform with a predetermined, sufficient accuracy. Thus, there will no longer be a scaling of the target waveform this time, and the actual output voltage will develop over time such that it will overlap the target waveform 508 if drawn in the same coordinate system.

In the case of fig. 5, it is advantageous to have the controller store the "learned lessons". Considering that the target waveform has to be scaled during generation of the most recent voltage waveform for some reason, it is likely that the same reason will still exist the next time a voltage waveform is to be generated. To reduce or avoid the need for repeated scaling of the same kind, the controller may store the final, scaled target waveform 508 as a new default target waveform to be applied next time. By more general definition, the controller may store information in volatile or non-volatile memory indicating effective measures for generating voltage waveforms found during one or more previous generation attempts. Such stored information is read for the purpose of generating an appropriate voltage waveform that follows the (scaled) target waveform, and is then considered as a form of receiving the scaling information via internal input 208.

In addition to or as an alternative to the voltage feedback information, the controller 105 may receive feedback of the output current of the voltage converter 103. Fig. 2 shows the current feedback input 205 of the controller 105, with the current feedback information coming from the current sense circuit 215 (coupling B-B).

The target waveform may be more complex than in the simple examples of fig. 3-5, so it includes two or more local extrema. The amplitude scaling explained above may affect the overall amplitude (amplitude at each point of the time axis) or only some parts thereof, such as only the maximum amplitude, or N maximum amplitudes where N is 2 or more. Additionally or alternatively, in particular, the dynamically performed amplitude scaling may only affect the maximum amplitude that will still occur, and/or only the amplitude of those half waves or other local extrema that will still occur.

Scaling the target waveform by amplitude alone tends to change the absolute value of its derivative. This is readily seen by comparison, for example, in the three sections of fig. 4. The first derivative of the graph is its steepness, i.e. the angle between the local tangent and the horizontal axis. The first derivative of each scaled down version of the graph in fig. 4 is significantly smaller than its predecessor (preprocessor). In some cases, it is advisable to scale to preserve the value of the derivative. This may require scaling the target waveform not only in amplitude but also in length of time.

Fig. 6 and 7 show examples where the target waveform is scaled with respect to both amplitude and length of time. The leftmost graphic 301 in fig. 6 shows an original target waveform, and the original target waveform is used when the configuration information indicates that there are N1 piezoelectric elements to be driven. Graphs 601 and 602 show the scaled target waveforms used when the configuration information indicates the presence of N2 or N3 piezoelectric elements, respectively, where N1< N2< N3.

The left-most graph 301 in fig. 7 again shows the original target waveform, which finds that the actual output voltage cannot follow at time 701. Arrows 702 and 703 illustrate how the original target waveform is scaled in amplitude and length of time to obtain a first scaled target waveform 704. At time 705, even if the first scaled target waveform is found to be untraceable, it is again scaled in amplitude and length of time to obtain a second scaled target waveform according to arrows 706 and 707, whose actual output voltage then follows from the point in time as illustrated by the rightmost graph 708 in FIG. 7.

Time scaling may also be used so that the amplitude of the target waveform remains constant and only its length in time (or the length in time of a portion of the target waveform) is changed. Time scaling may occur in two directions: the target waveform (or portion thereof) is made longer or shorter than previously. As illustrated in the example of fig. 8, wherein the left-most graph 801 shows the original target waveform used when the configuration information indicates that there are N1 piezoelectric elements to be driven. Graphs 802 and 803 show the scaled target waveforms used when the configuration information indicates the presence of N2 or N3 piezoelectric elements, respectively, where N1< N2< N3. The same principle, i.e. scaling the target waveform for a longer time, can also be applied to dynamic scaling.

Scaling the target waveform for a longer time may be advantageous for load handling, since a longer rise time towards the maximum amplitude value may ease the burden on the voltage converter.

Fig. 9 and 10 show two examples of methods for driving a piezoelectric element in a user interface device. In general, the method includes controllably generating a voltage waveform for driving the piezoelectric element, which may be one or more. The method comprises controlling the generation of the voltage waveform such that the generated voltage waveform follows a target waveform as a function of time. This is shown in both fig. 9 and 10 as an "execute waveform" step 901, which begins when a start command (e.g., an interrupt to the processor) arrives during the wait state 902. If the generation of the voltage waveform at step 901 proceeds as expected, more things happen and the execution of the method returns to the wait state 902 after the waveform is completed.

In fig. 9 and 10, it is assumed that feedback control is applied during generation of the voltage waveform. Thus, both fig. 9 and fig. 10 demonstrate how any small deviation from the target waveform detected by analyzing the feedback information results in performing feedback control according to step 903.

The methods of fig. 9 and 10 include scaling the target waveform based on the received scaling information. Fig. 9 relates to a case where at least part of the scaling information is received in advance as configuration information. In that case, scaling of the target waveform may also be done in advance, as shown in step 904. As explained previously herein, the scaling at step 904 may include scaling at least one of the amplitude and the length of time of the target waveform.

In fig. 10, at least part of the scaling information is dynamically received as feedback information during the generation of the voltage waveform in step 901. This occurs in fig. 10 as a "large" deviation from the currently valid target waveform and results in scaling of the target waveform in step 1001. What is a large deviation can be defined in a program executed by the controller. For example, the controller may be programmed to sample the feedback information it receives at a sampling frequency such that the obtained samples constitute a sequence. If a small deviation is first found and feedback control is attempted, but further values in the sequence show that the deviation is not getting smaller, this can be interpreted as a "large" deviation. Additionally or alternatively, there may be a threshold defined as an absolute or relative difference from the value of the target waveform at the respective time instant, which is immediately interpreted as a "large" deviation.

Whether or not feedback information is used for feedback control at step 903 and/or for determining scaling of the target waveform at step 1001, there is a possibility to use voltage feedback from the generation of the output voltage waveform and/or the output current for delivering the voltage waveform to the one or more piezoelectric elements. Considering that voltage converters are typically used for generating voltage waveforms, the control signals may be provided to the power switches in the voltage converter in the form of switching pulses. The method may then include varying at least one of a duty cycle and a switching frequency of the switching pulses such that an output voltage of the voltage converter follows a target waveform as a function of time.

Fig. 10 illustrates optional steps for resetting the target waveform to a default form at step 1002. This may be done, for example, if a timeout expires in wait state 902. Such a reset may be advantageous, for example, if scaling occurs at step 1001 due to some environmental conditions (e.g., extreme cold), it is expected that this will only happen from time to time, and thus, after a long period of inactivity, it is more likely that normal conditions will be restored.

In all of the embodiments explained above, it should be noted that the advance scaling of the target waveform (based on received configuration information) and the dynamic scaling of the target waveform (based on feedback information received during generation of the voltage waveform) are not mutually exclusive and may be applied in the same device. In other words, the piezo user interface device may be pre-configured to use a particular scaled target waveform and additionally apply dynamic controls to dynamically rescale the target waveform if necessary.

Scaling the target waveform does not mean that the entire target waveform needs to be scaled. The controller may decide to only scale portions of the target waveform. This is particularly applicable to such more general waveforms having two or more local extrema. Scaling may be particularly applicable to such extremes of the target waveform if one or some extreme conditions require the generation of a very high and/or very steeply varying voltage, which may require more effort than the generation of a more smoothly varying portion of the voltage waveform.

The same or similar mechanisms used to detect deviations in the target waveform may also be used to identify special cases (e.g., hardware faults). For example, a short circuit somewhere in the load may make it difficult or impossible for the generated voltage waveform to follow the target waveform. Such an abnormal situation may be identified by noting the need for an abnormally large scaling of the target waveform and/or rejecting a reduced difference from the target waveform despite scaling the target waveform. The controller may respond to the identified special case by interrupting any ongoing generation of voltage waveforms and reporting to the host, which may be a higher control computer in the device hierarchy. Additionally or alternatively, the controller may notify the user if the controller has a suitable device (e.g., an error indicator light) for its disposal.

In all cases involving scaling of the target waveform, it may be advantageous for the controller to report to the host. This reflects the fact that the user may receive slightly different haptic sensations due to zooming, which in turn may cause the user to react in some different way, and the host (or some other system, having some communication connection to the host) may need to be considered appropriately. Additionally or alternatively, there may be a notification threshold such that the controller may report all the cases to the host, wherein scaling of the target waveform involves scaling one or more dimensions of the target waveform by more than a respective threshold percentage.

The manner in which the hardware elements are organized into one or more integrated circuits and/or discrete electronic components is immaterial. As one example, at least a majority of the voltage converter and the controller may be implemented as a common single integrated circuit. As another example, a distributed hardware approach may be employed in which the voltage conversion and controller are separate circuits that may even be a significant distance from each other if the connections between them can be properly arranged.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, but they may vary within the scope of the claims.