JPH03217926A - Coordinate input device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a coordinate input device that inputs a coordinate position indicated by a coordinate pointing tool using, for example, the propagation of ultrasonic waves.

[Prior Art] An ultrasonic coordinate input device is one of the applied devices for distance measurement using ultrasonic waves. This pen has a piezoelectric element built into it, and transmits an ultrasonic signal emitted from a coordinate indicating pen that emits a desired ultrasonic signal from its tip through a propagating body such as a tablet. This propagation signal is detected by multiple sensors installed at the end of the propagation body, and the distance between the pen and each sensor is determined by measuring the arrival time to each sensor, and the distance between the pen and each sensor is determined. Calculating the coordinate position above.

[Problems to be Solved by the Invention] However, in the above conventional example, the distance between the pen and the sensor is calculated based on the propagation time of the ultrasonic signal, and the coordinate value of the indicated point is determined from this. The accuracy of is the coordinate accuracy itself. Therefore, if the propagation time fluctuates due to some external cause, an error will occur in the detected coordinate position. Possible causes of such fluctuations in the propagation time include instability of the pointing state, such as pen shake immediately after the pointing action and fluctuations in the pressure of the pen when pressing down on the pen. Furthermore, if the pen tip is not fixed at one point and moves, the signal arrival time will be slightly shifted, causing an error. Furthermore, even if the pen tip is placed at approximately one point, in unstable conditions where the pen pressure angle and writing pressure fluctuate, the gain and waveform of the sensor output signal will fluctuate. As a result, the signal arrival time similarly fluctuates, resulting in an error in the detected coordinate position.

The present invention has been made in view of the above conventional example, and an object of the present invention is to provide a coordinate input device that improves the accuracy of coordinate input values by examining fluctuations in signal arrival time at each sensor.

In addition, by examining the fluctuations in the calculation results of the coordinate values indicated by the coordinate indicating device, we can eliminate coordinate measurement errors caused by camera shake, constant pressure fluctuations, etc. that tend to occur at the beginning of the indicating operation, and accurately indicate the coordinate values indicated by the coordinate indicating device. An object of the present invention is to provide a coordinate input device that can detect a coordinate position.

[Means for Solving the Problems] In order to achieve the above object, the coordinate input device and device of the present invention has the following configuration. That is, it is a coordinate input device that recognizes the coordinates of a pointing point based on the propagation time for a signal emitted by a coordinate pointing device to reach each of a plurality of sensors set at various locations on a propagating body, and the coordinate input device recognizes the coordinates of a pointing point from the propagation time of a signal emitted by a coordinate pointing device to each of a plurality of sensors set at various locations on a propagating body. a measuring means for measuring a signal arrival time; a determining means for measuring a signal arrival time at predetermined time intervals by the measuring means and determining whether a difference in signal arrival time at each time is within a predetermined time; and the determining means. and calculating means for calculating the coordinate value indicated by the coordinate indicating tool based on the signal arrival time when it is determined that the time is within the predetermined time a predetermined number of times in succession.

[Operation] In the above configuration, the measuring means that measures the signal arrival time from the coordinate indicator to the sensor measures the signal arrival time at predetermined time intervals, and determines whether the difference in signal arrival time at each time is within the predetermined time. Determine. In this way, when it is determined that the time is within the predetermined time for a predetermined number of consecutive times, the coordinate value indicated by the coordinate indicator is calculated based on the signal arrival time.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Description of coordinate input device (FIGS. 1 to 7)] FIG. 1 is a block diagram showing a schematic configuration of a coordinate input device according to an embodiment.

In FIG. 1, 1 is an arithmetic control circuit that controls the entire device and detects the coordinate position, for example, a CPU 3 1 such as a microprocessor, a ROM 3 1 a that stores control programs for the CPU 31 and various data, and a CPU.
3 RAM used as work area for 1
It is equipped with b. 2 is a piezoelectric element drive circuit, Ben 9
A piezoelectric element built into the device is driven to generate an ultrasonic signal. 3 is a signal waveform detection circuit, which connects sensors 10a to 10.
A sensor signal from C is input, and its peak value or inflection point is determined and output to the arithmetic control circuit 1.

As a result, the arithmetic control circuit 1 receives the signal arrival time t. can be found.

Reference numeral 9 denotes a coordinate indicating tool (input pen), which has a piezoelectric element built therein, and oscillates a desired ultrasonic signal from its tip. Sensors 10a to 10c are provided around the propagation body l1, and receive ultrasonic signals emitted from the ben 9 via the propagation body 11. 11 is a propagation body, which serves as a propagation medium for ultrasonic signals, and is made of aluminum, glass, or the like. 12 is a vibration isolating material and is installed around the propagation body 11 so that reflected waves other than the direct waves from the pen 9 do not enter the sensor 10.

In the ultrasonic coordinate input device configured as described above, the coordinate values of the indicated point are calculated from the distances between the plurality of sensors and the indicated point indicated by the pen 9.

There are various methods of calculating the distance r between each of the sensors 10 and the indicated point, but basically it is calculated from the arrival time of the ultrasonic signal emitted from the Ben 9 to the sensor. For example, for a received signal waveform as shown in FIG. 2, full-wave rectification,
The envelope is taken, and its peak position or inflection point is determined by the signal arrival time t. It is stipulated that This allows r F
From Vg ' tg + (offset value), distance r
can be calculated.

However, when the arrival time is detected based on the envelope in this way, a certain amount of fluctuation inevitably occurs due to the influence of the magnitude of the signal output and the characteristics of the filter. Therefore, when even higher precision is required, finer precision is achieved by detecting the phase at an appropriate coordinate position and determining the phase arrival time t.

FIG. 4 shows the configuration of the signal waveform detection circuit 3 when measuring the arrival time (t., tp) of the ultrasonic signal, and FIG. 5 shows examples of each output waveform at that time.

In FIG. 4, 10 is a sensor, and a preamplifier 19 is installed very close to the sensor 10 to prevent noise from entering. The received signal thus amplified is converted into a one-sided envelope waveform (50 in FIG. 5) by the absolute value circuit 20 and the low-pass filter 21, and the envelope waveform is differentiated twice using the differentiating circuits 22 and 23. I do. The zero crossing point (envelope waveform inflection point) is extracted by the comparator 24 and set as the group arrival time t8. However, in order to extract only the zero cross point which is the inflection point of the envelope waveform, the t. Window signal for detection (
Set the wavy line 51) in Fig. 5, take the product with the comparator output, and find the first rising edge of tg (51) in Fig. 5.
2).

Similarly, the 1p signal is t. Based on the detection signal, the gate circuit 27 generates t, a detection window signal (dashed line 53 in FIG. 5).
is set, the sensor output signal is multiplied by the comparator output, and the first fall of the product is set as tp (54 in FIG. 5).

Ben 9 and sensor 1 when using the above detection method
A method of calculating the distance r between zeros will be explained next.

Group velocity V. When and the phase velocity vp are equal, r=v,
・It can be determined by t, + (offset value), but ■. In the case of ≠V, since the phase in the group shifts with the distance r, a step-like shape as shown in FIG. 6 is observed as t, and a conversion operation is required. These steps indicate the movement of the phase detection point.
The angle of each stage is translated by the period T of the signal. ■． and V. If the phase detection points are equal and a constant phase detection point can always be observed, such a staircase will not be possible, and a twist t of the straight line a will be obtained. Therefore, it is only necessary to convert t9 obtained stepwise into the original straight line. In other words, tpa master (VH/Vts) tg-toe
(tof: Off Yat Toi Direct) However, since t1 has a large fluctuation,? pt=nTLE(Vg/VJtg-
tar tp (where n is an integer value). Using the property, tpa= tp +TI I n t [ {( vg
/vp) tg-tar-tp}/T+0.51 to find t■, and calculate the distance r using the following formula.

r ” V p +. j p r ofof is an offset value.

The arithmetic control circuit 1 shown in the block diagram of FIG. 7 performs such coordinate detection processing.

[Description of Arithmetic Control Circuit (FIG. 7)] FIG. 7 is a block diagram showing the internal configuration of the arithmetic control circuit 1 in this embodiment, and each component and an outline of its operation will be described below.

In the figure, 31 is a microcomputer that controls the arithmetic control circuit 1 and the entire coordinate input device, and includes internal counters,
It has built-in ROM31a and RAM3lb. 33 is a timer (consisting of a counter) that measures a reference clock selected from the required resolution, and sends a start signal to the piezoelectric element drive circuit 2 to start driving the piezoelectric element in the ben 9. Start timing by outputting to . As a result, the start of measuring the time until the signal waveform is detected is synchronized with the signal generation timing by Ben 9.

Other circuits constituting each component will be explained in order.

First, the CPU 3t outputs a reset signal to the timer 33, etc., and clears them once. Thereafter, a signal is output to the piezoelectric element drive circuit 2 to drive the piezoelectric element inside the ben 9. As a result, the timer 33 starts counting time.

In this way, the ultrasonic waves generated by Ben 9 are transmitted to the sensors 10a~
10c, with a delay corresponding to each distance. The arrival timing signals from each of the sensors 10a to '10c obtained via the signal waveform detection circuit 3 are transmitted via the detection signal input port 35 to the latch circuits 34a to 10c.
34c. Each of the latch circuits 34a to 34c corresponds to each sensor 10a to 10c, and when each receives a timing signal that is a signal from the corresponding sensor, it latches the time value of the timer 33 at that time.
When the determination circuit 36 determines that all detection signals have been received, it outputs a signal to that effect to the CPU 31. As a result, the CPU 3 1 uses the latch circuit 34a.
- Read the signal arrival time to each sensor stored in 34c. Thereafter, the coordinate position of Ben 9 on propagation plate 11 is calculated through predetermined calculations.

Note that if the signal indicating the arrival of the signal is not input from the determination circuit 36 even after the maximum delay time has passed, it is assumed that no coordinates have been input by the pen 9, and the coordinate position is not calculated.
Execute the process after the previous reset process.

[Operation Description (Figs. 1 to 8)] Fig. 8 is a flowchart showing the processing in the coordinate input device of this embodiment, in which the coordinate position is specified by pressing the ben 9 from a no-input state. It is started by

Note that the control program that executes this process is in ROM3.
It is stored in 1a.

First, in step S1, the sampling number counter Cn
(included in RAM3lb). Next, among the plurality of sensors, for example, the group arrival time tg of sensor loa. and use this as t8 for comparison, R
Store in Rt of AM3 l b. Next, in step S3, tHa of the sensor 1'Oa is similarly fetched at regular time intervals and stored in Dt. And step S4
The value of Rt and the value of Dt are compared, and the difference is the predetermined value f2.
If it is less than 1, it is determined that the pen state is stable and the process proceeds to step S5. In steps S5 and 86, it is checked whether the pen stable state can be detected 20 times in a row. If the pen stable state has been detected 20 times in a row and it is determined that the pen is stable, the process proceeds to step S7, and all sensors (lOa~ 10c) (tg.t.) is taken in and the X-y coordinates are calculated.

Further, when the difference between Rt and Dt becomes 121 or more in step S4, it is determined that some kind of bend pressing abnormality has occurred, and the process returns to step S1, and the above-described process is executed again.

As explained above, according to this embodiment, whether the pressure of the ben 9 is stable or not is determined by the group arrival time t from one sensor. Since the discrimination is made only by the following, the discrimination algorithm becomes very simple. Further, there is an effect that the degree of freedom in setting the group velocity capture time interval or the number of captures can be increased to enable discrimination.

In addition, in this example, a method was shown to examine the fluctuations of only one sensor, but if the fluctuations of two or more sensors were examined, the algorithm would become a little more complicated, but it would be more reliable as a means of detecting pen stability. Needless to say, this will increase.

[Other Embodiments (FIGS. 9 and 10)] Next, a second embodiment of the present invention will be described using the flowchart shown in FIG.

This flowchart is executed when the pen is designated from a state of no input. The feature of this embodiment is that the stable state of the pen is examined by looking at changes in the calculation results of the coordinate values of the indicated point. First, in step Sll, the number of samplings is C. is reset to “0”. Next step S12
Then, all (tg, tt) of the sensors 10a to 10c are taken in and the coordinate values of the indicated point are calculated. This is for comparison (
x. y) in (Rx.Ry) of RAM3 lb.

Next, the process proceeds to step S13, where (tg.tp) is fetched and coordinate calculation is performed in the same manner as step S12 at a predetermined time interval. Then, the process proceeds to step S14, and the difference between the value of (Rx.Ry) stored in step S12 and (x, y) determined in step S13 is determined. When this difference is less than a predetermined value, the process advances to step S15, and step S1
5 and S16, it is determined that the pen state is stable if the difference between the X coordinate value, the y coordinate value, and (Rx, Ry) is equal to or less than a certain value for 20 times. On the other hand, in step S14, the coordinate value (x
, y) and (Rx.Ry) ( l x - Rx l
<T or ly−Ryl<T) is a predetermined value (T)
If the above occurs, it is determined that some abnormality has occurred, and the process returns to step Sll to perform the above-described operation again.

If it is determined in steps S14 to S16 that the difference in coordinate values is within the predetermined value 20 times in a row, and it is determined that the pen 9 is stable, the process proceeds to step S17, and (Rx, Ry) or the last measured value is determined. The coordinate values (x, y) are output to the outside as the coordinate values of the designated point.

Additionally, if the average value of x-y calculated so far (20 times in this example) is taken as the coordinate value of the indicated point, a more stable result can be outputted as the indicated point coordinate value. I can do it.

Such an embodiment is shown in FIG.

Here, the calculated coordinate values are integrated in step S25,
Finally, in step S27, the number of samples (here, 2
0 times) to calculate the average value and output the result.

In these second and third embodiments, since the coordinate values are calculated every time, the time required for one cycle is relatively longer than in the first embodiment described above, so that the number of samples is limited. For example, if it takes about 30 ms to take in (tg, tp) and calculate the coordinate values (x, y), sampling 5 times will take 150 ms. It doesn't matter how much.

As explained above, according to these embodiments, the stability of the signal arrival time of one or more sensors or the stability of the calculated (x, y) coordinate values is checked during coordinate input operation, and the pen state is checked. Since the (x, y) coordinate values after confirming stability can be output to the outside, it is possible to prevent a decrease in accuracy caused by instability of the pen state at the initial stage of pen operation.

[Effects of the Invention] As described above, according to the present invention, there is an effect that the accuracy of coordinate input values can be improved by examining fluctuations in signal arrival time at each sensor.

In addition, by examining the fluctuations in the calculation results of the coordinate values indicated by the coordinate indicating device, we can eliminate coordinate measurement errors caused by camera shake, constant pressure fluctuations, etc. that tend to occur at the beginning of the indicating operation, and accurately indicate the coordinate values indicated by the coordinate indicating device. This has the effect of being able to detect the coordinate position.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the coordinate input device of the embodiment. FIG. 2 is a diagram showing an example of the signal waveform detected by the sensor. FIG. 3 is a block diagram showing the processing system of the signal detected by the sensor. , Figure 4 is a block diagram showing the configuration of the signal waveform detection circuit, Figure 5 is a diagram showing example signal waveforms of each part of the signal waveform detection circuit, and Figure 6 explains the calculation of the distance r between the sensor and the pen. 7 is a block diagram showing the configuration of the arithmetic control circuit of the embodiment, FIG. 8 is a flowchart showing the coordinate detection process of the first embodiment, and FIG. 9 is the coordinate detection process of the second embodiment. The tenth is a flowchart showing the coordinate detection process of the third embodiment. In the figure, 1... Arithmetic control circuit, 2... Piezoelectric element drive circuit, 3... Signal waveform detection circuit, 9... Pen, 10a
~10c...Sensor, 11...Propagator, 12...
Vibration isolating material, l3... First stage amplifier, l9... Preamplifier, 20... Absolute value circuit, 21... Low-pass filter, 22... First differential, 23... Second differential , 24...
・Tg comparator, 25...Tp comparator, 2
6...Tg gate circuit, 27...Tp gate circuit,
31...CPU, 3la-ROM, 31b...RAM, 33...Timer, 34...Latch circuit, 36...Determination circuit. Patent applicant: Canon Inc., District 1, Figure 7

Claims (4)

[Claims] (1) A coordinate input device that recognizes the coordinates of a pointing point based on the propagation time for a signal emitted by a coordinate pointing device to reach each of a plurality of sensors set at various locations on a propagating body, wherein the coordinates of a pointing point are recognized by the coordinates of a signal emitted by a coordinate pointing device, a measuring means for measuring a signal arrival time at a predetermined time interval by the measuring means; a determining means for determining whether a difference in signal arrival time at each time is within a predetermined time; When the determining means determines that the time is within the predetermined time a predetermined number of times consecutively,
A coordinate input device comprising: calculation means for calculating coordinate values indicated by the coordinate pointing device based on the signal arrival time. (2) The calculating means calculates an average value of arrival times of signals from each sensor, and calculates the coordinate value indicated by the coordinate indicating device based on the average value. The coordinate input device according to item 1. (3) A coordinate input device that recognizes the coordinates of a pointing point based on the propagation time for a signal emitted by a coordinate pointing device to reach each of a plurality of sensors set at various locations on a propagating body, wherein the coordinates of a pointing point are recognized by the coordinates of a signal emitted by a coordinate pointing device, wherein a measuring means for measuring the arrival time of a signal; a coordinate position calculating means for calculating the coordinate position indicated by the coordinate indicating device based on the signal arrival time; a determining means for measuring coordinate positions at predetermined time intervals and determining whether a difference between the coordinate positions at each time is within a predetermined range; A coordinate input device comprising: output means for outputting the coordinate position as a coordinate value indicated by the pointing tool when the coordinate position is determined. (4) The coordinate input device according to claim 3, wherein the output means further comprises means for calculating an average of the coordinate values measured at the predetermined time interval.