GB2493043A

GB2493043A - Ultrasonic position sensing in three dimensions

Info

Publication number: GB2493043A
Application number: GB1206458.0A
Authority: GB
Inventors: Steven Lavache
Original assignee: Performance Designed Products Ltd
Current assignee: Performance Designed Products Ltd
Priority date: 2008-06-16
Filing date: 2008-06-16
Publication date: 2013-01-23
Anticipated expiration: 2028-06-16
Also published as: GB201206458D0; GB2493043B

Abstract

A position sensing system 2 dynamically reduces the effects of multipath reflections by dynamically adjusting the comparator 16 threshold in response to received signals 4. The system compares the time a signal takes to travel from a transmitter 8 in a mobile component 6 to a plurality of receivers 12 in a fixed component 10 and adjusts (increases) the comparator threshold if the difference in times measured by the receivers is too large. It may also reduce the threshold if any receiver does not detect a signal.

Description

WIRELESS POSITION SENSING IN THREE DIMENSIONS USING ULTRASOUND

The present invention relates to a method for improving the sensing of a position of a mobile component relative to a fixed component by dynamically adjusting the sensing circuit.

Many attempts have been made to sense position using ultrasound. An example of a known positioning system 102 is illustrated in Figure 1. Typically an ultrasonic signal 104 is sent from a mobile component 106, including a transmitter 108, and is received at a fixed component 110, including three or more receivers 112. The receivers 112 have a fixed spatial relationship to one another, and measuring the time of flight of the signal 104 from the transmitter 108 to the three or more receivers 112 enables a measure of distance to be made. By using three or more receivers 112, the differences in time of arrival and the consequent different distance measurements allow trigonometric calculations to be carried out to determine the three dimensional relationship between the mobile 106 and fixed 110 components. Thus far, the theory of ultrasound position sensing is well understood and stands up to close scrutiny.

However, the fixed component 110 is set up with inbuilt assumptions to provide the most accurate position sensing over the range of distances and room sizes in which the system 102 is to be used. The fixed component 110 set up must take into account the ability of the system to distinguish between original and reflected signals 4, the polling rate of the components 106, 110 and any discrepancies between the flight times sensed by the receivers 112. This necessarily requires a compromise in the setting of the amplifier gain and comparator threshold settings within the fixed component 110.

However, the compromise set up may result in erroneous readings by the fixed component 10. For example, during high polling rates, or within small rooms, reflected signals can be detected and processed by the fixed component 110 if the gain of the amplifiers 114 is too high or the trigger thresholds of the comparator (not shown) too low. This is caused by oversensitivity and as these reflected signals have not had time to drop to a low enough amplitude to be rejected. Additionally, if the gain of the amplifiers 114 is set too low or the trigger threshold of the comparator too high, then direct signals 4 are not detected by the fixed component 10, again resulting in erroneous readings.

As the position sensing system 102 has to detect a large number of signals in a short time, the use of a conventional amplitude gain control circuit means that adjustments to the threshold of the comparator or gain of the amplifier 114 are effected too slowly to solve these problems.

A fixed component which mitigates this problem, as claimed in Claim 1, is in accordance with a first aspect of the present invention.

The control unit may be further arranged to send a timeout signal to the feedback means when no signal is received within a time period and the feedback means is configured to adjust the signal processing means in response to a timeout signal. This enables the fixed component to be adjusted when no signal has been detected within the fixed component.

Preferably, the feedback means is arranged to decrease the threshold of the comparator in response to a timeout signal.

The feedback means may also calculate the average of the times recorded by the timers and adjust the signal processing means by large amount when the average of the times is above a predetermined value and by a small amount when the average of the times is below a predetermined value. This enables the variation of the signal processing means to be an appropriate amount for the strength of the signal that is received by the fixed component.

Alternatively, the signal processing means may be varied in incremental steps.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Figure 1 illustrates a prior art position sensing system; Figure 2 illustrates a position sensing system of the present invention; Figure 3 is a flow diagram illustrating a method of the present invention; Figure 4 is a flow diagram illustrating a method of the present invention; and Figures 5a to 5c illustrate possible times recorded by the timers of the position sensing system of the present invention.

The system for position sensing will now be described in more detail, with reference to the position sensing system 2 illustrated in Figure 2. In this system the mobile component 6 is wireless and has a battery power supply (not shown), a transmitter 8 and a transmitter controller 9 coupled to the transmitter 8. The transmitter controller 9 serves to control the transmission and idle modes of the transmitter 8 and also to deal with the necessary amplification and buffering of the signal 4.

With reference also to Figure 2, the fixed component 10 has a plurality of receivers 12 suitable for receiving a signal 4 sent by the transmitter B in the mobile component 6. The fixed component 10 also includes a sensing circuit 12 responsible for determining the position of the mobile component 6 as described below.

In use, as illustrated in Figure 3, the mobile component transmitter 8 sends a signal 4. The triggering an control of the signal 4 may be carried out as described in International Patent Publication No. 2009/022089 Al the disclosure of which is incorporated herein by reference.

The signal 4 is received by each receiver 12 of the fixed component 10 at different times due to their different proximity to the mobile component 6 (step 30). As each receiver 12 receives the signal 4 it passes the received signal 4 to the sensing circuit 14. The signal 4 is passed to a high gain amplifier 16 in Class C operation which serves to clip the incoming signal 4 to produce a generally square waveform. The waveform is then passed to an edge detector 18 in the receiver and timer control unit 20 which turns off a timer 22 associated with the receiver 12 which received the signal 4 (Step 32).

Once all the receivers 12 have received a signal 4 and the timers 22 have been stopped (Step 34), the times are passed to a control unit 24 which determines the differentials between the recorded times (Step 36). The differential is the difference between the longest and shortest time recorded by a timer 22. The control unit 24 then determines whether the differential is greater or less than a predetermined value (Step 38). If the differential is greater than a predetermined value, as illustrated with reference to times recorded by timers Tl to T4 in Figure Sa, then a signal is sent to a processor (not shown) within the control unit 24 (Step 38). A large differential is suggestive of errors caused by reflections. Upon receiving this signal the processor causes the gain of the amplifier 16 to be decreased (Step 40) thereby reducing the likelihood of error signals stopping a timer 22.

If the differential is less than a predetermined difference value, as illustrated with reference to times recorded by timers Ti to T4 in Figure 5b, then the times are passed to a distance calculator 26 which calculates the relative position of the components using the values stored in the timers 22 against each receiver 12 (Step 44). The 3-dimensional position of the mobile component 6 is then determinable using trigonometric calculations.

The gain of the amplifier may be reduced in any suitable way. For example, the gain may be decreased by a specified amount for every time that the differential is greater than the predetermined value. Alternatively, the reduction in the gain may be based upon the average of all of the time of flight readings. Where (as illustrated in Figure 5a) the average time of flight determined by each of timers Ti to T4 is small, there is a short distance between the mobile and fixed components. In this instance the reduction in gain will be large. Conversely, as illustrated in Figure 5c, where the average time of flight determined by each of timers Ti to T4 is large, there is a greater distance between the mobile and fixed components and the reduction in the amplifier's gain is smaller, or may even be negative.

The gain of the amplifier may be adjusted according to the results of several consecutive signals until the differential is no longer greater than the predetermined value.

The fixed component may also be arranged to determine that no signal was received by the receivers within a predetermined time period, herein referred to as a timeout (Step 50 Figure 4) and send a signal to the control unit (Step 52). If a timeout occurs for the timers in the fixed unit then the control unit increases the amplifier's gain by a set amount (Step 54). This can be repeated if timeouts occur within further predetermined periods of time until signals cause the timers to stop within the predetermined period of time.

A timeout may occur if none of the times are stopped within a predetermined time.

Alternatively, a timeout may occur when one or two timers are not stopped within the predetermined time.

In this way the sensing system can be adjusted dynamically to take into account the surroundings in which it is being used.

Optionally, the received signal may be processed using threshold adjustable comparators (not shown) or any other suitable device in the place of the amplifiers. In the case where threshold adjustable comparators are used the threshold is increased if the differentials are greater than a predetermined value and reduced if a timeout occurs.

Typically four receivers will be used which provides 4 possible triangulation solutions which may then be averaged or otherwise processed, for improved accuracy. Only three receivers may be used (providing a single triangulation solution) if lesser accuracy is required and this option is encompassed in the present application. More than four receivers may also be used, providing further increased accuracy but at greater manufacturing cost.

It is desirable that the signal sent between the transmitter and receiver is an ultrasonic frequency signal; however, any suitable frequency may be used.

Claims

<claim-text>CLAIMS1. A fixed component configured to perform position sensing of a wireless mobile component including a transmitter, the fixed component comprising: a) a plurality of receivers in a predetermined spaced-apart relationship, each receiver configured to receive a signal sent from the transmitter; b) a plurality of timers each timer being associated with a respective one of the plurality of receivers; c) signal processing means configured to process the signal received at each receiver; d) timer control means arranged to receive a processed signal and stop the respective timer generally at the time of reception of the received signal by each receiver; and e) feedback means arranged to determine the maximum difference between each of the times at which each timer was stopped, determine if the maximum difference is larger than a specified value and cause an adjustment to the signal processing means if the difference is larger than the specified value wherein the signal processing means comprises a comparator and adjusting the signal processing means comprises varying the threshold of the comparator, and the feedback means is arranged to increase the threshold of the comparator in response to determining that the maximum difference is larger than a specified value. a</claim-text> <claim-text>2. A fixed component according to Claim 1 wherein the feedback means is arranged to decrease the threshold of the comparator in response to a timeout signal.</claim-text> <claim-text>3. A fixed component substantially as herein described with reference to and as shown in any combination of Figures 2 to 5.Amendments to the claims have been filed as followsCLAIMS1. A fixed component configured to perform position sensing of a wireless mobile component including a transmitter, the fixed component comprising: a) a plurality of receivers in a predetermined spaced-apart relationship, each receiver configured to receive a signal sent from the transmitter; b) a plurality of timers each timer being associated with a respective one of the plurality of receivers; c) signal processing means configured to process the signal received at each receiver; (4 d) timer control means arranged to receive a processed signal and 1 stop the respective timer generally at the time of reception of the received signal by each receiver; and C" e) feedback means arranged to determine the maximum difference between each of the times at which each timer was stopped, determine if the maximum difference is larger than a specified value and cause an adjustment to the signal processing means if the difference is larger than the specified value wherein the signal processing means comprises a comparator and adjusting the signal processing means comprises varying the threshold of the comparator, and the feedback means is arranged to increase the threshold of the comparator in response to determining that the maximum difference is larger than a specified value.
2. A fixed component according to Claim 1 wherein the feedback means is arranged to decrease the threshold of the comparator in response to a timeout signal. (4 r (4 (4</claim-text>