GB2066469A

GB2066469A - Improvements in or Relating to Guidance Devices

Info

Publication number: GB2066469A
Application number: GB8040530A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-12-19
Filing date: 1980-12-18
Publication date: 1981-07-08

Abstract

The invention relates to guidance devices for the blind. Pulses of ultrasonic energy are transmitted by a transducer under the control of a monostable device, the frequency of operation of which is controlled by a range oscillator. Reflected pulses of ultrasonic energy are received by a transducer 11 and after amplification are applied to a commutating filter 16. A ramp generator 24 is controlled by a crossed NAND gate 25 so that the ramp voltage decreases when the gate 25 is reset and remains substantially constant when the gate is set. The pulses from the monostable device are used to reset the gate 25 and the output of the commutating filter 16 is applied to the set input of the gate through a non-linear amplifier 22. The ramp generator 24 controls a voltage controlled oscillator 26 to provide a variable frequency audio output and also controls an electric motor 29 to provide a variable frequency vibratory signal. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Guidance Devices This invention relates to guidance devices, and is particularly concerned with a device for use by the blind or those with impaired sight.

Guidance devices are known in which pulses of ultrasonic energy are transmitted and received after reflection from objects. The reception of a pulse has been used to indicate to the user of the device that the object is present. However, most known devices have suffered from various disadvantages, in particular, that it has not always been easy for the user to interpret the information provided by the device. Further, some known guidance device have been liable to interference from external noise and other simiiar devices, and have not been suitable for long-range operation.

Finally, some known devices have been insufficiently accurate, particularly at short-range.

It is an object of the invention to provide a guidance device which does not suffer from some or all of the disadvantages of known guidance devices.

From one aspect the invention consists in a guidance device comprising: means for transmitting pulses of ultrasonic energy; means for receiving reflected ultrasonic energy; means for generating a ramp voltage; means for initating said ramp generating means after the end of each of said transmitted pulses; means for arresting said ramp when a reflected signal is received; and means for providing an audible or vibratory signal, the frequency of which depends on the magnitude of said ramp voltage.

Preferably a device in accordance with the invention is capable of providing both an audible signal and a vibratory signal. However, a switch is provided to enable the vibratory signal to be cutoff in order to converse battery power.

Preferably the means for receiving reflected ultrasonic energy includes a variable gain amplifier, the gain of said amplifier being controlled so that it increases during a predetermined period after the transmission of each pulse of ultrasonic energy. Preferably the gain is increased in steps.

Preferably the received signals are applied to a filter which is designed to pass only a narrow band of frequencies centered on the frequency of the transmitted pulses. Preferably this filter is a commutating filter.

Preferably the received signals are passed through a non-linear amplifier designed to amplify only signals above a predetermined level. This non-linear amplifier may, for example, be a feedback amplifier in which the feed-back is decreased whenever the output of the amplifier exceeds a threshold value.

Preferably the vibratory signal is produced by means of an electric motor which serves to rotate an eccentric weight. The speed of the motor is controlled by the ramp generating means so that it is relatively high when the ramp is initiated, and decreases during the period of the ramp. On the other hand, the frequency of the audible signal is preferably relatively low at the commencement of the ramp and increases during the ramp period.

One method of performing the invention will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 a is a block diagram of the transmitter portion of a guidance device in accordance with the invention; Figure 1 b is a block diagram of the receiver portion of the guidance device; Figure 2 is a circuit diagram of a part of the receiver illustrated in Figure 1 b; Figure 3 is a circuit diagram of a further part of the receiver; and Figure 4 is a timing diagram showing conditions in various parts of the device.

Figure 1 a shows the transmitter of the device which includes an oscillator operating at a frequency of 400 kHz as indicated in line A of Figure 4. The output of this oscillator is applied to a decade counter 2, which provides a 40 kHz signal as indicated in line B of Figure 4. This signal is applied to an ultrasonic transducer 3 through a power amplifier 4. The power amplifier is controlled by a monostable 5 so that it transmits pulses of ultrasonic energy as indicated at line F of Figure 4. The length of these pulses can be controlled by means of a switch 6 which is part of a switch for changing the range of operation of the device.When the switch 6 is in the shortrange position (S), the duration of each pulse of ultrasonic energy may be, for example, 0.5 of a millisecond and, when the switch is in the longrange position (L), each pulse may be, for example, of 1 millisecond duration.

The transmitter illustrated also includes a range oscillator 7, the output of which is applied through two decade counters 8 and 9 to the monostable 5. The frequency of operation of the range oscillator 7 is controlled by contacts 6a of the range switch 6 so that the output of the decade counter 9 consists of alternate positivegoing and negative-going pulses each having the duration of 30 milliseconds when the range switch is in the short-range position (S), and a duration of 1 80 milliseconds when the range switch is in the long-range position (L). The general form of the output of the decade counter 9 is indicated at line C of Figure 4, and the general form of the output of the counter 8 is indicated at line D of Figure 4.The monostable 5 operates to produce a short pulse substantially coincident with the leading edge of each of the positivegoing pulses produced by the decade counter 9 as indicated at line F of Figure 4.

Figure 1 b of the drawings shows the receiver of the guidance device which includes an ultrasonic transducer 11, the output of which is applied through a fixed gain amplifier 12 to a swept gain amplifier 13. Outputs of the decade counter 8 are applied over multiple lines 31 through individual amplifiers 14 and resistors 15, only one of each of which is illustrated in Figure 1 b, to the swept gain amplifier 13 to increase its gain in a number of steps. In the particular example shown, eight of the ten outputs of the decade counter 8 are used to increase the gain in eight steps during a period of 6 milliseconds when the range switch is in the short-range position, and over a period of 36 milliseconds on long-range. The period of increasing gain is indicated at line E of Figure 4.

The output of the swept gain amplifier 13 is applied to a commutating filter 1 6. This filter includes ten capacitors 1 7 and ten transistors 1 8 connected in the inverted mode. The transistors 1 8 are individually controlled by ten further transistors 32, the bases of which are connected by ten lines to the outputs of the decade counter 2. Thus the filter 1 6 acts as a high-Q bandpass filter centred on 40 kHz. The operation of commutating filters is described, for example, on pages 54 to 56 of the October 1971 issue of "Design Electronics".

The output of the commutating filter is applied through a summing circuit 19, an amplifier 20, and a rectifier 21 to the input of a non-linear amplifier 22. The circuitry associated with the amplifier 20, the rectifier 21 and the non-linear amplifier 22 is illustrated in somewhat more detail in Figure 3 of the drawings. In this figure the amplifier 20 is represented by the operational trans-conductance amplifier IC3 and the output of the summing circuit 19 is applied to pin 2 of IC3.

Feedback from the output of IC3 is applied through R40 to pin 3 of IC3 and the gain of this amplifier is pre-set by means of a potentiometer VR1, one end of which is connected to the negative supply and the other end of which is connected through a resistor R38 to the positive supply. The rectifier 21 of Figure 1 b is shown in Figure 3 as a pair of series-connected diodes D2 and D5. The detector circuit also includes a capacitor C20 and a resistor R45.

The non-linear amplifier 22 is shown as an operational amplifier IC4, pin 3 of which is connected through a resistor R46 to the output of the detector circuit. The operational amplifier is arranged so that it does not respond to the DC level of the signal or associated noise and small low-level reflected signals. Large signals, on the other hand, are amplified considerably. To produce this result, the output of the operational amplifier is connected through a resistor R47 to pin 2 and this pin is also connected to the emitter of a transistor T26, the base and collector of which are connected to earth through respective resistors R44 and R33. The transistor T26 is nonconductive for low input signals but conductive for signals above a pre-determined level.Thus the gain of the amplifier is reduced by heavy feedback during reception of the low-level signals, and is increased by reduction of the feedback when the input signals rise above the pre-determined level.

A generator 24 is provided to develop a ramp voltage which decreases from a maximum value when operation of the generator is initiated, as shown in line G of Figure 4. The generator is illustrated in more detail in Figure 2 and includes a capacitor C23 which is charged during the ramp period through a switching transistorT23 and a charging resistor. A switch SW3 constitutes part of the range switch 6, so that during short range operation the charging resistor is constituted solely by the resistor R81,while for long-range operation it is constituted by the resistors R81 and R82 in series. The time constants of the capacitor charging circuit are arranged so that the duration of the ramp voltage is approximately 6 milliseconds on short-range and 26 milliseconds on long-range.The output of the monostable 5 is connected to the generator 24 over a line 34 and a delay circuit 35 and serves to discharge the capacitor during each transmitted pulse. The delay circuit 35 is shown in Figure 2 as constituted by a resistor R60 and a capacitor C26.

The line 34 from the monostable 5 is connected to a terminal 36. The delay network operates in conjunction with the first gate G1 of a Schmitt NAND gate to provide a delay of 200 microseconds. The delay network produces a saw-tooth wave which the second halfG2 of the Schmitt NAND gate inverts. The inverted signal is applied through a potentiometer consisting of resistors R50 and R51 to the base of a grounded emitter transistor T22. The collector of the transistor T22 is connected to a balanced-T network consisting of resistors R52 and R53 and a transistorT27. The emitter-collector path of transistor T27 is connected in series with a resistor R54 across the capacitor C23. The resistor R54 has a low value so that, when the transistorT27 is conductive, the capacitor C23 is rapidly discharged.The circuitry associated with the transistor T22 serves to switch the transistor T27 between a non-conductive state and a fully conductive state in response to the delayed pulse from the monostable 5.

The output of the monostable 5 is also connected through the delay circuit 35 and a NAND gate G3 to the reset input of a crossed NAND gate 25, and the output of the non-linear amplifier 22 is connected to the set input of this gate through a logic interface 37. The logic interface 37 is represented in Figure 2 by a transistorT25 and a NAND gate G4. The output of the non-linear amplifier 22 is connected to the base of the transistorT25 through a resistor R48.

The collector of the transistor T25 is connected directly to the zero supply line while the emitter is connected to the negative supply line through the parallel combination of a resistor R49 and a capacitor C22. The output of the NAND gate G.4 is connected to one input of a NAND gate G5 which together with a further NAND gate G6 constitutes the crossed NAND gate 25. The logic interface serves to change the level of any signal from the output of the non-linear amplifier 22 so that it is effective to set the crossed-NAND gate 25. The output of the crossed-NAND gate is connected through a resistor R55 to the base of the switching transistor T23, and serves to turn this transistor on when the gate is in the reset condition.Thus the capacitor C23 commences to charge shortly after the occurrence of each transmitted pulse so that the ampiitude of the ramp voltage commences to decrease. When a signal is applied to the set input of the crossed NAND gate from the non-linear amplifier 22, the gate is changed to the set condition and the switching transistor T23 is rendered non conductive. Thus further charging of the capacitor is inhibited and the ramp voltage stays at substantially the same level until the capacitor is discharged during the next transmitted pulse.

The output of the ramp generator 24 is connected to a function generator or voltage controlled oscillator 26, the output of which is connected through an amplifier 27 to a sound reproducing device (not shown). The frequency of the audio output of the function generator is controlled by the ramp voltage so that the higher the level of the ramp voltage, the lower the frequency of the audio output. As can be seen from Figure 2, a transistor T24 is provided between the output of the ramp generator and the input of the function generator. This transistor is connected as an emitter follower so that it provides a high-impedance interface between the ramp generator and the function generator. The base of the transistor T24 is connected directly to the collector of the transistor T23 while the collector of T24 is connected directly to the positive supply iine.The emitter of the transistor T24 is connected through a decoupling circuit consisting of a resistor R58 and a capacitor C24 and through a variable resistor BR3 to pin 5 of IC6 which constitutes the function generator. The high impedance interface is necessary to ensure that the capacitor C23 is not discharged by any load constituted by the succeeding circuits when the transistors T23 and T27 are non-conductive.

the variable resistor VR3 enables the function generator to be set to a specific level of signal before an audio output is provided. The frequency of the audio output, which appears on pin 3 of IC6, is pre-set by means of the capacitors C25 and C27.

The output of the ramp generator is also connected through an amplifier 28 to a d.c. motor 29. The input to the amplifier 28 is taken from the junction of resistors R58 and VR3 through a further resistor R61 (Fig. 2). In this case, the arrangement is such that the higher the level of the ramp voltage, the higher the speed of rotation of the d.c. motor 29. The d.c. motor drives an eccentric weight which serves to produce ,vibrations whose frequency depends directly on the level of the ramp voltage.

It will be understood that an ultrasonic signal will be received by the device 6 milliseconds after the transmission of a pulse of ultrasonic energy if the transmitted pulse is reflected from an object located at approximately 1 metre from the device.

Similarly, a pulse will be received by the device after 36 milliseconds if the transmitted pulse is reflected by an object at a distance of approximately 6 metres from the device.

Thus, when the range switch is in the shortrange position, if the transducers are directed towards a stationary object located at less than 1 metre from the transducers, a substantially continuous audible note will be heard, the frequency of which will be dependent on the distance of the object. If, on the other hand, there is no object within 1 metre from the transducers, only short pulses will be heard, each pulse being in the form of a note of increasing pitch. In an alternative arrangement, a further gate is included in the ramp generator so that there is no output from the ramp generator until the crossed-NAND gate has been set by a reflected pulse. In this case, no sound will be heard unless there is an object within 1 metre from the device.

Similar conditions apply when the range switch is in the long-range position except that, in this case, a signal of a specific frequency is heard when ultrasonic energy is reflected from an object within 6 metres from the device.

It is to be understood that a single transducer may be used in place of the two transducers 3 and 11, suitable switching means being provided to connect the power amplifier 4 and the fixed gain amplifier 1 2 alternately to the transducer. It is therefore also to be understood that references to "transmitting means" and "receiving means" in the preceding statement of invention and the following claims do not exclude the possibility that a part or parts of these means are common.

Claims

1. A guidance device comprising: means for transmitting pulses of ultrasonic energy; means for receiving reflected ultrasonic energy; means for generating a ramp voltage; means for initiating said ramp generating means after the end of each of said transmitted pulses; means for arresting said ramp when a reflected signal is received; and means for providing an audible or vibratory signal, the frequency of which depends on the magnitude of said ramp voltage.

2. A guidance device as claimed in Claim 1 including means for providing both an audible signal and a vibratory signal and switch means for cutting off the vibratory signal.

3. A guidance device as claimed in Claim 1 or Claim 2 wherein the means for receiving reflected ultrasonic energy includes a variable gain amplifier, the gain of said amplifier being controlled so that it increases during a predetermined period after the transmission of each pulse of ultrasonic energy.

4. A guidance device as claimed in Claim 3 wherein the gain of said variable gain amplifier is increased in steps.

5. A guidance device as claimed in any of the preceding claims wherein said means for receiving reflected ultrasonic energy includes a filter designed to pass only a narrow band of frequencies centred on the frequency of the transmitted pulses.

6. A guidance device as claimed in Claim 5 wherein said filter is a commutating filter.

7. A guidance device as claimed in any of the preceding claims wherein said means for receiving reflected ultrasonic energy includes a non-iinear amplifier designed to amplify only signals above a predetermined level.

8. A guidance device as claimed in Claim 7 wherein said non-linear amplifier is a feedback amplifier in which the feedback is decreased whenever the output of the amplifier exceeds a threshold value.

9. A guidance device as claimed in any of the preceding claims wherein the vibratory signal is produced by means of an electric motor which serves to rotate an eccentric weight.

10. A guidance device as claimed in Claim 9 wherein the speed of said electric motor is controlled by the ramp generating means so that it is relatively high when the ramp voltage is high and decreases with any decrease in the ramp voltage.

11. A guidance device as claimed in any of the preceding claims wherein the frequency of the audible signal is relatively low when the ramp voltage is high and increases with any decrease in the ramp voltage.

12. A guidance device as claimed in any of the preceding claims including a range switch arranged to control the duration of each pulse of ultrasonic energy, the rate at which said pulses of ultrasonic energy are transmitted, and the slope of said ramp.

1 3. A guidance device as claimed in Claim 12 when dependent on Claim 3 or Claim 4, wherein said range switch also controls the period during which the gain of said amplifier is increased.

14. A guidance device as claimed in Claim 13 including an oscillator, the frequency of operation of which is controlled by said range switch, wherein the output of said oscillator is fed through frequency dividing means to said variable gain amplifier and through further frequency dividing means to a monostable device which controls the means for transmitting ultrasonic pulses and also serves to initiate the generation of said ramp voltage.

1 5. A guidance device substantially as hereinbefore described with reference to and as illustrated in the accompanying diagrammatic drawings.

1 6. Any features of novelty taken singly or in combination of the guidance device hereinbefore described with reference to the accompanying diagrammatic drawings.