WO1989009924A1

WO1989009924A1 - Method and apparatus for measuring distance travelled along a gradient

Info

Publication number: WO1989009924A1
Application number: PCT/GB1989/000350
Authority: WO
Inventors: Peter S. Cruttwell; David Cockburn Cosserat
Original assignee: Cruttwell Peter S; David Cockburn Cosserat
Priority date: 1988-04-05
Filing date: 1989-04-05
Publication date: 1989-10-19
Also published as: AU3366489A; GB8807850D0

Abstract

Distance travelled over a gradient is determined by measuring atmospheric pressure at a point on a path to be travelled in order to obtain an altitude value. The measurement is repeated at another point on the path travelled, and by determining the difference in altitude values and applying a factor corresponding to the slope of the gradient, the distance between said points is determined. A device operating according to this method and intended particularly for use by a skier comprises an absolute atmospheric pressure sensor (3) coupled to a programmed microprocessor (1) and having appropriate manual controls (2) and a visual display (7). The slope factor may be entered in the microprocessor as an estimated value or as a value measured by an inclinometer (8) provided on the device.

Description

METHOD AND APPARATUS FOR MEASURING DISTANCE TRAVELLED ALONG A GRADIENT

This invention concerns a method and apparatus for measuring distance travelled along a gradient.

It is an object of the invention to provide a means for ascertaining distance travelled on a gradient, in circumstances where a direct measurement by means of a sensor in contact with the ground, e.g. a wheel coupled with an odometer, is not possible or not desirable. one particular application contemplated for the invention is use by a downhill skier, who may wish to establish a measurement of distance travelled, or average speed, over a particular ski-run.

In accordance with the invention the measure of distance travelled over a particular gradient is obtained by measuring a net change in altitude in terms of a corresponding change in atmospheric pressure following travel over a path having a given gradient, and calculating the distance travelled along the gradient from correspondingly established values for the vertical distance travelled and the inclination of the gradient.

Thus one embodiment of the device in accordance with the invention may include an altimeter, means for receiving a signal representative of a gradient, and means for processing output signals from the altimeter together with said gradient signal, in order to derive a distance measurement from a change in altitude. Preferably, the means for receiving the gradient signal is coupled to a manual input enabling selection of a given gradient, for example numerically.

For example, an implementation of the invention to provide a measuring device for use by a skier may take advantage of the fact that ski-slopes ('pistes') are universally classified in ascending order of difficulty according principally to their angles, i.e. Green, Blue, Red and Black. Although there are frequently within a given colour short sections of another colour or colours, the overall classification permits the assignment to it of an average percentage slope, e.g. Green = 7%, Red 12% etc. Thus the gradient signal could be derived from correspondingly coloured control buttons. A skier wishing to use the device thus has only to select that colour button to press at the start of his trip which best represents the type of ground over which he plans to ski. He can change the setting at will should the terrain change significantly; or he can use a digital button which will permit him to prescribe an average degree of slope so as to compensate for frequent amplitudes without having therefore con¬ stantly to re-select the setting.

Another arrangment may provide for the gradient signal to be obtained by direct measurement, using an inclino¬ meter.

In a further preferred development of the invention, the means for calculating distance may comprise a micro- processor programmed to respond to one or more further input signals in addition to the altitude and gradient signals. Thus, for example, a further input signal may be provided from a digital clock in order to enable calculation of average speed travelled. A further input signal may be provided from a thermal sensor, for example for the purpose of correcting the output signal from a temperature sensitive altimeter in accord¬ ance with stored calibration data.

According to a yet further preferred feature of the invention, the microprocessor may be arranged to receive a succession of gradient input signals from a programable, or pre-programmed unit which stores gradient data unique to a particular ski-run.

it will be appreciated that in addition to processing such various input signals for the purpose of displaying distance or average speed, the microprocessor may be programmed to provide optional displays of other data available from the respective input units coupled thereto, e.g. the functions of a digital watch or stopwatch; barometer; altimeter or thermometer.

The invention is illustrated by way of example in the accompanying drawings, in which;

Fig. 1 is a block circuit diagram of one embodiment of a device in accordance with the invention,

Fig. 2 is a more detailed circuit diagram of another embodiment of the invention, and

Fig. 3 is a view showing the layout of the liquid crystal display of the device of Fig. 3, together with function and control switches.

Referring to Fig. 1, the reference numeral 1 indicates a microprocessor with an associated digital clock, read only memory containing the operating program of the microprocessor, and random access memory for storage of data to be processed. Reference numeral 2 indicates manually operable switches for providing input data to the microprocessor and/or selecting functions thereof.

Reference numerals 3 and 4 respectively indicate analogue atmospheric pressure and temperature sensors. Alternatively these sensors may be substituted by a single pressure sensing device not compensated internally for temperature. Reference numeral 5 indicates an analogue to digital converter arranged to receive, in multiplex, the signals from the sensors 3 and 4 and to provide corresponding data to the microprocessor. Reference numeral 6 indicates a memory storing temperature response characteristics of the pressure sensor 3. Reference numeral 7 indicates a digital display for providing visible output data.

An inclinometer being a slope measuring device may be mounted on the side of a casing of the device according to the invention and may be actuated by means of a button on the top adjoining which is a telescopic sight and fish eye lens. The reading obtained can then be manually relayed into the microprocessor. A preferred alternative is for this information to be fed electronically into the A-D converter 5 by way of a strain gauge 8 forming part of the inclinometer.

The device illustrated may be utilised to provide the functions outlined generally above. For example, by means of the input controls 2, the operator may select the desired function of the microprocessor 1, input specific gradient data, and/or select a particular program of stored gradient data relating to a specific route to be travelled. In accordance with the program related to the selected function of the microprocessor 1, the latter will receive input data and provide a corresponding visible output via display 7. For example, pressure and temperature measurements will be received from sensors 3 and 4, the calibration store 6 being interrogated to enable the output signals of the pressure sensor to be corrected in accordance with given temperature readings. From successive readings of the pressure sensor 3 the vertical distance travelled can be established, and by correlating vertical distance with gradient information derived from the input 2 and/or from a memory containing stored data, or alternatively the internal electronic slope measuring sensor described above, the distance travelled over the ground can be established and displayed, or, optionally, utilised to provide an indication of average speed.

Barometer readings for the time four, eight and twelve hours previously are available from stored data.

Referring now to Fig.2 there is shown a more detailed circuit diagram of a specific embodiment of the invention. The circuit comprises standard commercially available integrated circuits which are designated in the drawing by identifying serial numbers from which one skilled in the art will appreciate the functioning of each circuit. The construction of the individual integrated circuits will not therefore be referred to in greater detail except as necessary to explain the functioning of the circuit as a whole. Also, it will be appreciated that to enable identification of the connections of the individual components the corresponding commercially utilised pin numbering of each component is illustrated in the drawing and that the use of similar reference numerals to identify pins of different components does not imply any common relationship between pins of different devices that are illustrated by the same reference numeral.

In Fig. 2 a pressure transducer is illustrated at PT1. The transducer is of the type commercially available as Motorola MTX100 and is a non-internally temperature compensated absolute pressure transducer. The transducer generates a voltage between pins 2 and 4 which is proportional to absolute atmospheric pressure. To achieve this a standing current must be supplied between pins 3 and 1 and this is generated via a resistor chain R3, R4, R5 connected between a voltage source VCC and ground via a switching transistor TR1. The switching transistor is biased by resistors Rl and R2 connected as a voltage divider between the voltage source VCC and pin 4 of a microprocessor indicated generally at 40.

An integrated circuit U2 serving as an analogue multiplexor has control pins 9 and 10 coupled to pins 5 and 8 of the microprocessor 40, and in accordance with corresponding control signals received from the microprocessor is arranged to couple any one of a plurality of pairs of input terminals X0, Y0; XI, Yl; X2, Y2; and X3, Y3 to a corresponding pair of output terminals X and Y. Output terminal X is coupled via an operational amplifier Ul/1 and resistor R6 to the emitter of a transistor TR3 whereas the output Y of the circuit U2 is connected via operational amplifier Ul/2 to the base of transistor TR3. The operational amplifiers Ul/1 and Ul/2 serve as buffers whereby the output voltage appearing across the outputs X and Y of integrated circuit U2 is effectively applied across the resistor R6. The collector of transistor TR3 is connected on the one hand via resistor R8 and a switching transistor TR2, to ground, and, on the other hand to the inverting input of an operational amplifier Ul/3 connected, together with feedback capacitor C3, to form an integrator. The non-inverting input of operational amplifier Ul/3 is connected to a source of reference voltage provided by voltage divider network R7, R18 and RIO connected between the collector of transistor TR1 and ground. The base of transistor TR2 is connected via resistor R9 to one output Q/ of an integrated circuit U3/1 forming a bistable multivibrator. The circuit U3/1 is arranged to receive an input signal on pin D from the output of operational amplifier Ul/3, and to receive at the input CLK a clocking signal provided from an output pin 9 of integrated circuit U7. The latter provides a buffered output from a crystal oscillator circuit indicated generally at 41. The pin 9 of integrated circuit U7 provides a signal at the frequency of the oscillator 41, whereas a further output 3 of the integrated circuit u7 provides a signal at a very much reduced frequency to a clocking input CLK of a further bistable multivibrator U3/2 of which an output Q is coupled to pin 14 of microprocessor 40 to provide an interrupt signal. A further pin 11 of the microprocessor 40 is coupled to a resetting input PRE/ of the integrated circuit U3/2.

The microprocessor 40 is driven by means of a clock oscillator crystal 42 having a frequency significantly higher than that of the clock oscillator 41 and is programmed by means of an EPROM 43 to calculate measurements of atmospheric pressure, temperature and time from signals provided by the circuit elements described above, and under manual controls provided by actuation of push buttons PBl and PB2,and to display corresponding output information on a liquid crystal display 44.

The manner in which pressure and temperature are measured will now be explained in further detail.

The resistance of the pressure transducer PT1 between pins 3 and 1 varies according to ambient temperature in a predetermined manner. As the temperature changes, this therefore causes a change in the current flowing in the resistor chain R3, R4, R5 and, consequently, a change in the voltage across resistor R4. In order to avoid unnecessary current drain on an internal battery of the device, the transistor TR1 is switched by means of the microprocessor 40 so that a current flow is established through the pressure^' transducer PT1 only for the duration of each measurement. After transistor TR1 has been switched on by the microprocessor 40 as described above, signals are applied to the multiplexor U2 in order to couple inputs X3 and Y3 to outputs X and Y. This serves to stabilise the integrator circuit provided by operational amplifier Ul/3 in a predetermined condition. The corresponding output signal from the operational amplifer Ul/3 and applied at input D of bistable U3/1 is such that the latter is set to a condition in which the output Q/ is high and transistor TR2 is switched OFF. The microprocessor 40 then causes multiplexor U2 to couple inputs XI, Yl to outputs X and Y, whereby resistor R4 is connected across the non-inverting inputs of operational amplifiers Ul/1 and Ul/2 and there appears at the non-inverting input of operational amplifier Ul/3 a voltage signal corresponding to the voltage drop across resistor R4. Operational amplifier Ul/3 causes the capacitor C3 to charge at a rate proportional to this input signal until, at a predetermined output voltage. the bistable U3/1 changes state and provides a pulse at output Q which is applied to input 15 of the micro¬ processor 40. The corresponding change of signal at output Q/ serves to switch on transistor TR2 whereby capacitor C3 is discharged at a constant rate through R8, causing resetting of the bistable U3/1. The micro¬ processor is programmed to maintain the input signal to operational amplifier Ul/3 for a comparatively long period of time, e.g. 250 milliseconds, during which the switching of the bistable U3/1 is repeated continu¬ ously and the output signal applied from the bistable to the input 15 -of the microprocessor 40 thus comprises a rectangular pulse train of which the frequency is proportional to the temperature of the pressure trans- ducer PTl. . The microprocessor 40 is programmed to perform an appropriate calculation by counting the input pulses received at pin 15 for a predetermined period of time to derive an absolute temperature signal. To take account of variations in individual pressure transducers, a read-only memory 45 is provided to store calibration data relating to the pressure transducer PTl and to enable the microprocessor 40 to perform an appropriate correction on the calculated data.

Measurement of pressure is carried out in a manner similar to that described above with the exception that the microprocessor causes the multiplexor U2 to couple inputs X0 Y0 to outputs X and Y, to enable measurement of the pressure-dependent voltage appearing across pins

2 and 4 of the pressure transducer. Furthermore, since the pressure transducer is not temperature compensated, the final calculation of absolute pressure is obtained by deriving measured values for both temperature and pressure and calculating a final pressure from both readings together with corresponding calibration data stored in read-only memory 45. The calibration data stored in the read-only memory 45 is provided at the time of manufacture of the device. Advantageously, the microprocessor 40 is also programmed in such a manner as to enable the calibration data to be derived and stored in the memory 45 during an initial calibration of the complete device after assembly. In such a calibration step the complete device is subjected to a predetermined cycle of ambient temperature and pressure variation wherein predetermined pressure and temperature values are established over a defined period of time and the correspondingly measured values are utilised by the microprocessor 40 to store calibration data in the memory 45.

It- will be appreciated that the microprocessor 40 may be programmed in any desired manner to provide on the output display 44 data appropriate to manual commands input via push button switches PBl and PB2. However, an example of a specific display is illustrated in Fig. 3 which shows the layout of a liquid crystal display together with associated push buttons. It will be appreciated that the figure shows all available individual elements of the liquid crystal display, whereas, in use, only selected elements of the display will be visible at a given time as determined by the microprocessor 40.

Thus, it will be noted that the liquid crystal display comprises a digital display indicated generally at 100, of the kind commonly utilised in digital watches or clocks. In addition to the normal set of four digits utilised to display timekeeping, a fifth digit is provided for the purpose of displaying slope data as described below. Above the digital display there are arranged a number of individually selectable function identifiers indicated collectively at 101, whereas to the right of the display there are provided a set of individually selectable parameter identifiers indi¬ cated collectively at 102. Below the digital display are located further optionally selectable ^• identifiers relevant to corresponding groups of digits. The two push buttons indicated at 103 and 104 respectively are identified as function and control switches.

The microprocessor 40 is programmed in such a way that by consecutive manual activation of the function switch 103 individual modes of operation of the microprocessor appropriate to the individual functions 101 may be selected. The microprocessor is further programmed so that in each function mode control commands and data may be input manually using the control switch 104.

The manner in which the selection of individual functions and the entry of data appropriate to the relevant functions is achieved by means of only two push buttons will be familiar to those skilled in the art of digital watches, and thus a detailed description of the corresponding programming of the microprocessor 40 will be omitted for brevity.

In the barometer mode a display of barometric pressure in millibars may be selected on the digital display. In this mode the control button 104 may be operated to select stored readings of barometric pressure obtained over a period of time. Readings at elapsed times of 4, 8 and 12 hours may, for example, be obtained in order to enable weather changes to be assessed.

By selecting the altitude mode, an altitude reading may be obtained as calculated by the microprocessor in terms of the measured barometric pressure. To take account of changes in barometric pressure with time, the control button 104 may be utilised for calibration of the device at a known altitude. The control button may also be utilised to enable altitude readings to be provided either in feet or metres.

Upon selection of the distance function, a reading of distance travelled may be obtained by causing the microprocessor to calculate distance from a measured change in altitude taking into account a slope factor entered manually by the user of the device utilising the control button 104. For example, the programme provided for the microprocessor may enable the slope factor to be entered utilising the control button 104 and subsequent activations of the control button 104 then to provide an indication of the starting and stopp¬ ing, or intermediate, instants in a time period for which a distance measurement is to be calculated.

It will be appreciated that various algorithms may be utilised to perform such a calculation and the deri¬ vation of any appropriate algorithm will be a routine matter for one skilled in the art of programming a microprocessor. Suffice it to say that upon commencement of a time period defined by the control button 104 the microprocessor will make a pressure measurement and calculate an altitude value. At the end of one or more time intervals defined by actuation of the control button 104 and/or by the programming of the micro¬ processor, a further pressure measurement and altitude calculation will be made. By calculating the difference in altitude readings and applying this together with the stored data defining the slope factor in an appro¬ priate sine function, a corresponding value of distance travelled along the slope can be calculated. - 13 -

Selection of the speed function may be utilised to cause the microprocessor to perform a speed calculation by relating calculated distance and elapsed time, and to display the calculated speed in units as selected by the control button 104.

Clock alarm date and stop watch functions may be provided in the manner conventional for digital watches.

Selection of the temperature function enables the user to obtain a digital readout of ambient temperature as measured in the manner described above. The readout may be provided in degrees Celcius or degrees Fahrenheit at the option of the user by activation of the control button 104.

Claims

Claims ;

1. A method for measuring a distance between points on a gradient comprising the steps of, providing a factor related to the slope of said gradient, measuring the altitude at a point on said gradient by sensing atmospheric pressure at that point, likewise measuring the altitude at another point on said gradient, calculat¬ ing the difference between said measured altitudes, and applying said calculated difference and said slope factor in a further calculation to obtain a distance value.

2. A method as claimed in claim 1, wherein said gradi¬ ent is a ski slope, and said steps are carried out by a skier travelling said slope.

3. A method as claimed in claim 2, wherein said alti¬ tude measurements are effected by means of an atmospheric pressure sensor under the control of a programmed micro¬ processor, and said calculations are effected with the aid of said microprocessor.

4. A method as claimed in claim 3, wherein said slope factor is estimated and stored in a memory of said microprocessor.

5. A method as claimed in claim 3, wherein said slope factor is measured with an inclinometer and stored in said microprocessor.

6. A device for use in determining distance between points on a gradient, comprising an altimeter, means for receiving and storing a value representative of a slope factor, and a microprocessor programmed to interrogate said altimater at determined intervals of time and to calculate a distance value utilising differing altitude values and the stored slope factor value.

7. A device according to claim 6 further comprising manual controls for entering said slope factor value in a memory of the microprocessor and for determining points in time at which said altimeter is to be interro¬ gated to define said distance.

8. A device according to claim 6, wherein said alti¬ meter comprises an absolute atmospheric pressure sensor an analogue output of which is arranged to be coupled to said microprocessor via an analogue to digital con¬ verter.

9. A device according to claim 8, wherein a temperature sensor is arranged to be coupled to said microprocessor via an analogue to' digital converter and said micro¬ processor is programmed to correct pressure values provided by said pressure sensor in accordance with measured temperatures.

10. A device according to claim 9, wherein said pressure and temperature sensors are provided by different elec- trical current paths of the same device, both of said current paths being coupled to the same analogue to digital converter by means of a multiplexor controlled by said microprocessor.