GB2296616A - Setting up distance measurement device - Google Patents

Abstract

Device 1 measures the distance to target T and assigns it to one of three range bands. By means of inputs 3 and 4 a user first sets the distance to a reference point in the measurement range of the device, and then sets the boundaries of the range bands relative to this reference point. This has the advantage that if the device is knocked or moved, only the distance to the reference point needs to be reset in a single operation; all the boundaries are then reset automatically. The reference point may be a boundary, or midway between the boundary points. Application to conveyor belts or traffic monitoring is mentioned. <IMAGE>

Description

DISTANCE MEASURING DEVICE The present invention relates to a distance measuring device that measures a distance to an object.

More specifically, the invention relates to a distance measuring device that, when the range of distance measurement of the device is divided into a plurality of distance measurement areas, judges to which of the predetermined areas the distance measurement result of the device belongs, and which outputs the result of the judgement.

A distance measuring device is known which, when the range of distance measurement of the device is divided into a plurality of distance measurement areas, judges to which of the plurality of areas the distance measured by the device belongs, and which outputs the result of the judgement. For example, when the range of distance measurement of a distance measurement device is divided into three distance measurement areas Z61, Z62, and Z63, as shown in Figure 8(c), a far side division point, Pa, and a near side division point, Pb, can be set by two division-point set means independently of each other, as shown in Figures 8(a) and 8(b). At this time, for example, 16 different fixed division points (PaO to Pal5 and PbO to Pub15) can be set with combinations of the voltage levels of input terminals each having four bits.

Figure 7 shows a known distance measurement device acting as an object detecting device M for detecting articles travelling on belt conveyors BC1, BC2, and BC3 of width, w, arranged in parallel. If the right hand end of the belt conveyor BC1 as shown in Figure 7 is set as division point Pb and the right hand end of the belt conveyor BC2 as shown in Figure 7 is set as division point Pa, then it will be possible to judge that an article S belongs to the distance area Z61 when it is on the belt conveyor BC1, to the distance area Z62 when it is on the belt conveyor BC2, and to the distance area Z63 when it is on the belt conveyor BC3.

However, in the known device the far side division point Pa and the near side division point Pb are set separately by two independent division-point set means, and so the distance division points Pa and Pb both have to be reset to new distances by two division-point set means when the distance between the object detecting device M and the belt conveyor was changed (in Figure 7, when the object detecting device M was moved from the position indicated by solid lines to the position indicated by broken lines).

Also, a similar problem arose in the investigation of a quantity of traffic on a road the width of a passage to be investigated is desired to be set to a specified distance value multiplied by a predetermined rate.

The present invention therefore seeks to provide a distance measuring device that, in a situation in which the width or rate of a distance area desired to be detected has been fixed, can easily set the distance area, while overcoming the problems described above.

According to the present invention there is provided a distance measuring device comprising: distance measurement for means measuring a distance to an object within a measurable distance range; setting means comprising first set means for setting a specific distance point within the measurable distance range and second set means for setting at least one division point at a position relative to the specific distance point; the distance measurement device also comprising judgment means for judging to which of the distance ranges the distance measurement result of said distance measurement means belongs, out of a plurality of distance ranges divided by division points set by the setting means.

The second set means may be set means which sets predetermined equal distances on the near and far sides of said specified distance point, respectively.

Also, the second set means may be set means which sets predetermined distances on the near side or far side of said specific distance point. The second set means may also be set means which sets distances represented by a predetermined rate of a distance value of the specific distance point, on the near side or far side of said specific distance point.

Also, said judgement means includes computation means for converting states of said set means and another set means and the distance measurement result of said distance measurement means to comparable states.

Further, in order to make said computation means simply and achieve the simplification of the judgement circuit, the device may further comprise storage means having distance information on a distance point that said first set means and said second set means can set.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a circuit block diagram showing a distance measuring device of a first embodiment of the present invention.

Figure 2 is a diagram indicating the operation of the first embodiment of the present invention.

Figure 3 is a graph indicating the judgement method of the judgement means of the present invention.

Figure 4 is a diagram indicating the relationship between a division point and a distance area of the present invention.

Figure 5 is a diagram indicating the relationship between a division point and a distance area of the present invention.

Figure 6 is a circuit block diagram showing a distance measurement device of a second embodiment of the present invention.

Figure 7 is a diagram indicating the problems to be solved by the invention.

Figure 8 is a diagram of a known distance measuring device.

The present invention will hereinafter be described in detail in accordance with embodiments shown in the accompanying drawings.

Figure 1 is a circuit block diagram showing a first embodiment of the present invention. For simplicity, the situation in which a range of distance measurement is divided into three distance areas by two distance division points set on the near and far sides of one specific distance point by a first and second set means, respectively, is shown. In Figure 1, reference numeral 1 denotes distance measurement means for measuring a distance to an object T and for converting the result to a digital signal to output it.

The distance measurement means may comprise, for example, means which emits infrared rays and detects light reflected from the object T with a position sensing device (PSD) or means using ultrasonic waves.

Reference numeral 3 denotes first set means such as digital switch means by means of which the voltage levels of a plurality of signal lines are changed. In Figure 1, four signal lines 3a, 3b, 3c, and 3d, are shown and 16 settings are possible with combinations of the voltage levels of the signal lines. The set means 3 sets a specific distance point (hereinafter referred to as a specific point) of the distance measurement range of the above-described distance measurement means 1.

Reference numeral 4 denotes second set means. As with the set means 3, 16 settings are possible with four signal lines 4a, 4b, 4c, and 4d. The second set means sets predetermined distance ranges AL on the near and far sides of the specific point set by the abovedescribed first set means 3.

This relationship will be described with reference to Figure 2. In the Figure, the axis represents a distance L from the distance measurement means 1. The farthest point is LF (for example, 3.7 m), and the nearest point is LN (for example, 0.5 m). Consider now a case where a range of distance measurement (LNF) is divided into 16 equal parts and the 16 settings by the set means 3 are applied to this.

Assuming that the above-described specific point is PA, then the specific point PA can be set to any of distance points PAn (where n is a natural number between 0 and 15), as shown in Figure 2(a). In Figure 2, the specific point PA has been set to PA8 (n = 8), and a distance from the distance measurement means 1 becomes 2.1 m (0.5 m + 0.2 x 8 m).

Although the second set means 4 can set 16 different distance ranges AL, consider now a situation in which one step is 5 cm. Assuming that a near side distance point separated from the specific point PA by a distance range At is PB1 (hereinafter referred to as a division point PB1) and a far side distance point separated from the specific point PA by a distance range AL is PB2 (hereinafter referred to as a division point PB2), then the division points PB1 and PB2 can be set in a range between 1.3 m (2.1 m - 0.05 m x 16) and 2.9 m (2.1 m + 0.05 x 16) at intervals of 10 cm. In Figure 2(b), the second set means has been set to the eighth step, i.e., 40 cm have been set with respect to 2.1 m, and the distance measurement means 1 are to be set to 1.7 m and 2.5 m.

While in the above-described embodiment the distance range AL of the second set means has been constant (one step = 5 cm), this distance range AL may be set to specific values (for example, 2, 4, 5, 10, ..., 25, 30, and 50 cm) with combinations of the set positions of the second set means 4, i.e., the voltage levels of four signal lines 4a, 4b, 4c, and 4d.

Returning to Figure 1, reference numeral 2 denotes judgement means, which judges to which area of the three distance areas Z1, Z2, and Z3 (see Figures 2(c)) which are divided at the division point PB1 and PB2 the distance measurement result of the distance measurement means 1 belongs. Also, the judgement means 2 outputs the result of the judgement to output terminals 01, 02, and 03. If, for example, the distance measurement result of the distance measurement result of the distance measurement meas 1 is 1.1 m, it will be in the distance area Z1 and therefore only 01 will be set to a high voltage level. Likewise, if the distance measurement result of the distance measurement means 1 is 2.2 m, it will be in the distance area Z2 and therefore only 02 will be set to a high voltage level.

If the distance measurement result of the distance measurement means 1 is 2.8 m, it will be in the distance area Z3 and therefore only the voltage on 03 will be set to a high voltage level.

When the distance measurement result of the distance measurement means 1 is outside the distance measurement range LNF, outputs different from usual may be performed. For example, all of the output terminals 01 to 03 may be set to high voltage levels, or the result may be output to an additional output terminal.

Next, an actual judgment method of the judgment means 2 will be described. The distance measurement means 1 first emits an infrared ray toward an object T and then receives the reflected light with a position sensing device (hereinafter referred to as a PSD). If the distance to the object T changes, the position of light incident on the PSD will change. The PSD converts the position of the incident light into currents in two directions such as il and i2. In this case, the current il corresponds to the current of the short distance end of the PSD, and the current i2 corresponds to the current of the long distance end of the PSD. From the currents il and i2 that were output in that way, the following number NP which first corresponds to a distance to the object T is obtained based on Equation (1).

NP = il / (il + i2) (1) In this equation, the number NP is substantially proportional to the inverse number of the distance L.

Therefore, in order to judge to which area the distance measurement result of the distance measurement means 1 belongs, it is necessary that the states of the abovedescribed division points PB1 and PB2, which were set by the first set means 3 or the second set means 4, are converted into mutually comparable quantities and compared. Reference numeral 2a in Figure 1 represents computation means for performing this computation.

Figure 3 is a graph showing the relationship between the above-described number NP and the distance L from the distance measurement means 1 to the object T. The numbers corresponding to the nearest point LN and farthest point LF are values that are determined by the structure of the distance measurement means 1, and these numbers are assumed to be NPN and NPF, respectively.

If it is now assumed that the pulse number equivalent to the distance value LP of the division point that is set is NPx, the following Equations (2) to (4) will be given.

NPx = (NPN - NPF) (1/LP - 1/LN)/(1/LN - 1/LF) + NPN (2) LPB1 = LPA - AL x m (3) LPB2 = LPA + AL x m (4) where LPA is the distance value of the specific point PA, and LPB1 and LPB2 are the distance values of the division points PB1 and PB2, respectively. (m is a natural number between 1 and 16.) LBP1 or LPB2 is substituted in LP.

While it has been described that the distances LPB1 and LPB2 of the division points PB1 and PB2 are 1.7 m and 2.5 m, respectively, these values are based on the result of calculation of the above-described Equations (3) and (4). Assuming now that NPN = 800, NPF = 200, and the pulse numbers of the above described division points are NPB1 and NPB2, then NPB1 = 310 and NPB2 = 245 will be obtained by the above-described Equation (2). Therefore, when the number of the distance measurement result of the distance measurement means 1 is less than 245, the distance measurement result can be judged to belong to the distance area Z3.

When the pulse number of the distance measurement result of the distance measurement means 1 is more than 245 and less than 310, the distance measurement result can be judged to belong to the distance area Z2. When the pulse number of the distance measurement result of the distance measurement means 1 is more than 310, the distance measurement result can be judged to belong the distance area Z1.

While in the above embodiment the number NP has been assumed to be substantially proportional to the inverse number of the distance L and has been computed according to Equation (2), a correction term may be added to this equation, or accuracy of judgement can be increased by using an optimum equation, depending on the kind of the distance measurement means.

Further, since in the above-described embodiments the second set means 4 has set equal distance ranges on the near and far sides of the specific point PA, the distance between the division points PB2 and PB1 is constant even if the distance of the specific point PA is changed. However, distance ranges represented by a predetermined percentage of the distance value of the specific point PA may be set on the near and far sides of the specific point PA, depending on the application.

That is, the second set means can set, for example, 2%, 4k. 6k, ..., 10%, 15, and 20k. When 15 is set and the distance of the specific point is set to 2.1 m by the first set means 3, the division point PB1 is set to 1.785 m (2.1 m x 0.85) and the division point PB2 is set to 2.415 m (2.1 m x 1.15). Also, when the specific point PA is set to 1.4 m, the division point PB1 is set to 1.19 m (1.4 m x 0.85) and the division point PB2 is set to 1.61 m (1.4 m x 1.15). Therefore, if the distance of the specific point PA changes, the space between the division points PB2 and PB1 will change.

While in the above-described embodiments, equal distance ranges have been on the near and far sides of the specific point PA, a ratio of the near side distance and the far side distance may be a predetermined value. That is, the second set means sets the distance of a difference between the division points PB1 and PB2 to 16 kinds (for example, 60 cm), and, for example, a ratio of 30W (18 cm) and 70% (42 cm) is set on the near and far sides of the specific point PA.

Further, as a method of setting the second set means, various modifications are possible as follows.

Figures 4 and 5 show the relationship between a division point and a distance area.

Figure 4 is a case where the second set means sets a predetermined distance range on only the far side of the specific point PA set by the first set means. The second set means can be set to 16 steps at intervals of, for example, 10 cm. If the specific point PA is PA6 (1.7 m) when the second set means is set to the eighth step, i.e., 80 cm, the division point PB3 will be 2.5 cm (1.7 m + 0.8 m). And, the distance measurement range is divided at the specific point PA and division point PB3 into three distance areas Z1, Z2, and Z3.

Likewise, Figure 5 shows a situation in which the second set means sets a predetermined distance range on only the near side of the specific point PA set by the first set means. The second set means can be set to 16 steps at intervals of, for example, 10 cm. If the specific point PA is PA10 (2.5 m) when the second set means is set to the eighth step, i.e., 80 cm, the division point PB4 will be 1.7 m (2.5 m - 0.8 m). And, the distance measurement range is divided at the specific point PA and division point PB4 into three distance areas Z1, Z2, and Z3.

Next, a second embodiment of the present invention will be described in accordance with Figure 6. Figure 6 is a circuit block diagram showing a second embodiment. In Figure 6, reference numeral 62, as with the first embodiment, is judgment means that judges to which distance area the result of distance measurement of distance measurement means 1 belongs. Reference numeral 5 is storage means. The same reference numerals will be applied to the same parts as Figure 1.

The storage means 5 stores the information having values calculated in advance with Equations (3) and (4) described in the first embodiment regarding the division points PB1 and PB2 corresponding to the settings of the first set means 3 and the second set means 4.

If in Figure 6 the first set means 3 and the second set means 4 are set, the judgement means 62 will read out the distance values of the division points PB1 and PB2 from the above-described storage means 5. An area to which the result belongs is judged by converting the result to a corresponding number NP with Equation (2) and by comparing the converted result with the distance measurement result of the distance measurement means 1. Therefore, it becomes unnecessary for the judgement means 62 to perform the calculation of Equations (3) and (4).

Also, while in the above-described embodiment the distance value has been stored in the storage means 5, a number NP corresponding to the distance value calculated in advance by the above-described Equations (2), (3), and (4) may be stored directly. With this, the calculation of the above-described Equation (2) becomes unnecessary and the structure of the judgement means 62 can be made simpler.

While in the above-described first and second embodiments the distance measurement range LNF has been divided at the specific point PA equally, the present invention is not limited to this. The division width may be changed according to a predetermined rule based on a relationship such as a fractional function or a logarithmic function. Various modifications, such as where the division width is made fine at a short distance and rough at a long distance, are possible.

Further, although in the above embodiments it has been described that, for simplicity, two division points are set with one specific point and a range of measurement is divided into three distance areas, the present invention is not limited to this. Increasing distance areas is also possible, for example, by setting four division points with two specific points and by setting five distance areas.

Further, although in the above embodiments the set means 3 and 4 have been made so that 16 kinds of division points or specific points can be set with signal lines of four bits, the number of bits may be increased or decreased.

In accordance with one use of the present invention, for example, in an object detecting device for detecting articles travelling on belt conveyors arranged in parallel, when the distance of installation between the object detecting device and the belt conveyor is changed, it is necessary only to reset the first set means by measuring a distance between the object detecting device and one end or centre of the belt conveyor. Therefore, it becomes unnecessary to carry out a procedure whereby the distance to a plurality of belt conveyors or one belt conveyor is measured, the width of the belt conveyor is added to the measured value to calculate two distances, and the first set means and the second set means are both reset.

Also, in a further use of the invention where in the investigation of a quantity of traffic on a road the width of a passage to be investigated is set to a specified distance value multiplied by a predetermined rate, even when the width of the road is changed, it is necessary only to reset the first set means.

Thus, there can be provided according to the present invention a distance measurement device that, in a case the width or rate of a distance area desired to be detected has been fixed, can easily set the distance area even when the place of installation of an object detecting device is changed.

Claims (11)

Claims

1. A distance measuring device comprising: distance measurement means for measuring a distance to an object within a measurable distance range; setting means comprising first set means for setting a specific distance point within the measurable distance range and second set means for setting at least one division point at a position relative to the specific distance point; the distance measurement device also comprising judgment means for judging to which of the distance ranges the distance measurement result of said distance measurement means belongs, out of a plurality of distance ranges divided by division points set by the setting means.

2. A distance measuring device as claimed in claim 1, wherein the specific distance point set by the first set means is a division point for dividing the plurality of distance ranges.

3. A distance measuring device as claimed in any preceding claim, wherein the setting means is connected to the judgement means.

4. A distance measuring device as claimed in any preceding claim, wherein the second set means sets at least two division points, one on either side of the specific distance point.

5. A distance measuring device as claimed in claim 4, wherein said second set means sets division points at preset equal distances on either side of said specific distance point.

6. A distance measuring device as claimed in any preceding claim, wherein said the or at least one division point set by the second set means is set at a distance represented by a predetermined rate of a distance value of the specific distance point.

7. A distance measuring device as claimed in any preceding claim, wherein the judgement means includes computation means for converting states of said first and second set means and the distance measurement result of said distance measurement means to comparable variable values.

8. A distance measuring device as claimed in any preceding claim further comprising: a storage means for storing information regarding each division point corresponding to the set states of the first set means and the second set means.

9. A distance measuring device as claimed in any preceding claim, wherein the first and second set means are digital switches having signal lines connected to the judgement means.

10. A distance measuring device substantially as herein described with reference to Figures 1-5 and 7 or Figures 2-7 of the accompanying drawings.

11. A distance measurement device comprising: distance measurement means for measuring a distance to an object; judgment means for judging the result of the distance measurement of said distance measurement means; first set means connected to said judgment means for setting a specific distance point of a distance measurement range said distance measurement means can measure; and second set means for setting one distance point on the near side of said specific distance point and for also setting one distance point on the far side of said specific distance point; wherein, among a plurality of distance areas divided with the distance point set by said second set means or a plurality of distance areas divided with said specific distance point and the distance point set by said second set means, said judgment means judges which of the distance areas the distance measurement result of said distance measurement means belongs to.