GB2076203A - Taximeters - Google Patents

Abstract

A fare accumulation system has two mode operation, below a break speed being on a time basis and above that speed on a distance travelled basis. Distance pulses and a sawtooth timing wave are produced, and above the break speed distance pulses occur with sufficient frequency to be used in suppressing the full timing wave, which is reset at each distance pulse. The distance pulses then determine the accumulation of fare units. Below break speed, the timing wave can reach a peak between distance pulses, and these peaks also generate fare accumulation. Any further time before the next distance pulse is also accounted for by adding a partial fare increment to the accumulator, corresponding to the instantaneous amplitude of the sawtooth at that next distance pulse. <IMAGE>

Description

SPECIFICATION Improvements relating to taximeters This invention relates to taxi meters, and is concerned with the electronic accumulation of the fare.

It is frequently required of taximeters that they compute the fare payable in any hiring on a combined basis of time and distance. In the Metropolitan Police Area (M.P.A.) this requirement is so defined that, if the taxi is stationary or travelling slowly, the fare accumulation shall take place on a time basis only and that, if the taxi is travelling at higher speed then fare accumulation shall depend solely on the distance covered. The dividing point is known as the break" speed, and is defined as follows: Distance corresponding to one fare unit Break Speed = ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Time corresponding to one fare unit It follows that below break speed one "time" equivalent of a fare unit will elapse before one "distance" equivalent is covered, while above such speed the reverse holds.

To give current figures for the M.P.A., the fare unit distance is 530 yards and the fare unit time is 180 seconds and so the break speed is: 530 yards 0.310 miles = = ~~~~~~~ = 6.02 m.p.h.

180 seconds 0.05 hours For an electronic taxi meter, distance information is provided by a rotating transducer driven from the vehicle's gear box. Every mile a typical transducer might perform 204 revolutions with six pulses per revolution. Thus one pulse corresponds to: 1760 1 ~~~~~~~~ = 1.437 yards = part of a 204X6 3.686 fare unit Time information for fare calculation is derived from a counter-timer which is set to generate a similar fraction of a fare unit every interval T, so that 1 T = x 180 seconds = 0.4883 seconds 368.6 Hence, every time the taximeter detects either a distance transducer pulse or a counter-timer demand it must add 1/368.6 of a fare unit to its fare accumulator, this fraction being referred to herein as a fare increment. Of course, it could have another numerical value depending on the distance transducer and the fare unit distance.

However, this system requires measures to ensure that the taxi meter operates either in the distance mode or the time mode and that there is no mutual interference to give a false accumulation.

According to one aspect of the present invention there is provided a fare accumulator system for a taxi meter having two modes of accumulation either side of a break speed, as hereinbefore defined, wherein there is a pulsed input from a distance transducer and a sawtooth input from a timer, each pulse or complete tooth being capable of adding a fare increment to an accumulator, wherein at each pulse it is determined whether the previous fare increment was generated by the timer, a negative answer causing one standard fare increment to be added to the accumulator while the timer is reset and its contents ignored, and an affirmative answer causing the instantaneous content of the timer to he added to the accumulator as a partial fare increment, the timer to be reset and the pulse to be ignored for fare calculation, and wherein any complete tooth, uninterrupted by a pulse, causes a fare increment to be added to the accumulator.

According to another aspect of the present invention there is provided a fare accumulator system for a taximeter comprising a computer programmed to enter in an accumulator, during a hiring, fare increments derived from a resettable timer and from pulsed distance signals, there being two modes of accumulation either side of a break speed as hereinbefore defined, wherein each distance pulse causes: the contents of the timer to be read and the timer to be reset, the determination of whether or not the timer produced the last increment to be accumulated, and the addition of either the instantaneous contents of the timer at the reset or a fixed fraction to the accumulator, depending on whether the previous determination was affirmative or negative, and wherein the timer is reset, unless reset by a distance pulse, a fixed time interval after the previous reset, and upon such fixed interval resets said fixed fraction is added to said accumulator Preferably, means are provided for determining when the accumulator attains or exceeds a given count corresponding to a completer fare unit, and for then deducting that given count to leave zero or a remainder that contributes to a following accumulation, each complete fare unit so determined being registered elsewhere.

When the fare increments total or just exceed a single whole fare unit, that unit will be added to a display. With the fraction 1/368.6 referred to above, there will have to 369 increments.

The remaining 0.4 of the last fraction is saved and will contribute to a subsequent fare unit.

For a better understanding of the invention an embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram showing the relationship between distance transducer and the timer outputs above break speed, Figure 2 is a diagram showing the relationship between those outputs below break speed, Figure 3 is a block diagram of a selection circuit for a taximeter accumulator, and Figure 4 is a flow chart of a fare accumulator system using a microprocessor.

In Fig. 1 the distance transducer pulses are dominant, and before each tooth from the timer can achieve its target level another distance pulse arrives and is used to inhibit the timer by resetting it. In other words, if the period between pulses is less than T there will be no timing demand.

In Fig. 2 the pulse period is greater than T. Thus the timer's output teeth attain the target level and instantaneously return to zero. This is used to add a fare increment. However, before the next full tooth, a distance pulse arrives, and resets the timer. This must not cause a complete fare increment to be added, for the taximeter is now in the time mode, but neither must the resultant partial fare increment represented by the small, shaded sawtooth, be lost or left unaccounted. The arrangement here is for the distance pulse itself to be ignored for fare calculation, and for the partial fare increment represented by the shaded area to be added to the accumulator.

Of course, at very slow speeds there could be two or more complete sawteeth between distance pulses.

Fig. 3 shows how this selection from distance and timing signals might be made. A distance transducer 1 produces the pulses and a timer 2 the sawtooth waveform described above. The resetting of the timer at each distance pulse whatever the mode is indicated by line 3.

The distance pulses are applied to an AND gate 4 which, if open, passes them via OR gate 5 to an accumulator 6 and via OR gate 7 to an input S of bistable 8. A pulse at input S results in a high output at 0 and an open AND gate 4.

The timer output is applied via a threshold detector 9 to input R of the bistable and to the OR gate 5. If the threshold is attained (this is the same as the target level of Figs. 1 and 2) then a pulse similar to a distance pulse is generated and a fare increment is added. Also, the bistable is reset, blocking the AND gate 4.

A further AND gate 10 receives the distance pulses and the Q output from the bistable, and a latch circuit 11 receives and follows the timer output and that of gate 10. When a distance pulse occurs with Q high gate 10 enables circuit 11, which then transmits its current state, representing the instantaneous timer content, to the accumulator. The output of the gate 10 is also applied to OR gate 7.

It will be seen that for Fig. 1, above break speed, the timer 2 is repeatedly reset before the threshold detector 9 can respond, and with Q high and Q low the distance pulses are maintaining the bistable in that condition and passing to the accumulator 6 as fare increments.

There is no timer output through circuit 11 since AND gate 10 is blocked by output Q.

Below break speed (Fig. 2) the threshold detector 9 resets the bistable upon completion of a full tooth and a fare increment is added. Since a distance pulse does not occur at this time, gate 10 remains blocked and there is no timer output through gate 11. However, when the next distance pulse occurs it finds the AND gate 4 blocked but AND gate 10 still open, since output O is high. The instantaneous content of timer 2 is therefore transmitted by circuit 11 to be added as a partial fare increment. The pulse from gate 10 is also used to change the state of the bistable 8 again, via OR gate 7 and input S, in case the speed increases and the next distance pulse occurs before completion of a full timer sawtooth, and thus block circuit 11 again.

In practice, rather than the gates 4 and 5 passing a simple '1' derived from the distance pulses to the accumulator 6, it would preferably be arranged that a fixed count corresponding to the interval T in micro-seconds would be entered (4.88334 in the M.P.A. case mentioned at the beginning). Likewise, each full timing pulse would contribute similarly to that count. Any fractional time contributions through circuit 11 would be consistent with this, for example adding 100,000 if that many microseconds had elapsed since the previous reset. Once the accumulator reaches or exceeds a count corresponding to one fare unit, that unit is added to the main display and the exact fare unit count (180 X 106 in the M.P.A. example) is deducted from the accumulator. Any remainder stays to contribute to the next accumulation.This accounts not only for the partial time pulses (the shaded zones in Fig. 2) but also for the remainder when the number of fare increments needed in theory to add a single whole fare unit is not an integer (368.6) and in practice the next highest whole number (369) is used. Thus when operating on distance pulses, and assuming the accumulator was originally at zero, after 369 distance pulses it will register a fare unit, and be left with 1 95246 after the deduction. The next 369 pulses will leave it with 390492, but only 368 pulses will then be necessary to take the accumulator past the 180 x 106 mark and generate the next fare unit addition. The remainder 97404 is carried over, and so on.

Another approach is to use a suitable programmed microprocessor, and a flowchart is illustrated in Fig. 4. Generally this is self-explanatory, but the following points should be noted.

The symbol "Return to Main Program" arises because both the wheel pulses and the timer demands appear in the form of "interrupts". These cause the microprocessor to depart from its main program and return to where it left off only when it has dealt with the relevant interrupt routine. Both these forms of interrupt are synchronously independent, both from each other and the main program, but in the case of simultaneous interrupts they will be serviced sequentially.

The "previous demand" bit is a statement made during the timer demand that such a demand has occurred, i.e. it indicates that the last increment was derived from the timer; It is interrogated during the wheel pulse routine, and reset if found to be set once the contents of the timer have been transferred to the accumulator.

Variations in the flowchart are possible. For example, the interrogation at the start of the timer routine is not strictly necessary, since it can be arranged to disable the timer when the taxi is not under hire. Also, the similar interrogation towards the end of the wheel or distance pulse routine is a repetition which can be eliminated by exchanging the two "increment" processes and moving the re-entry point from the earlier "Hired?" interrogation to between the exchanged "increment" processes.

Claims (4)

1. A fare accumulator system for a taximeter having two modes of accumulation either side of a break speed, as hereinbefore defined, wherein there is a pulsed input from a distance transducer and a sawtooth input from a timer, each pulse or complete tooth being capable of adding a fare increment to an accumulator, wherein at each pulse it is determined whether the previous fare increment was generated by the timer, a negative answer causing one standard fare increment to be added to the accumulator while the timer is reset and its contents ignored, and an affirmative answer causing the instantaneous content of the timer to be added to the accumulator as a partial fare increment, the timer to be reset and the pulse to be ignored for fare calculation, and wherein any complete tooth, uninterrupted by a pulse, causes a fare increment to be added to the accumulator.

2. A fare accumulator system for a taximeter, comprising a computer programmed to enter in an accumulator, during a hiring, fare increments derived from a resettable timer and from pulsed distance signals, there being two modes of accumulation either side of a break speed as hereinbefore defined, wherein each distance pulses causes: the contents of the timer to be read and the timer to be reset, the determination of whether or not the timer produced the last increment to be accumulated, and the additions of either the instantaneous contents of the timer at the reset or a fixed fraction to the accumulator, depending on whether the previous determination was affirmative or negative, and wherein the timer is reset, unless reset by a distance pulse, a fixed time interval after the previous reset, and upon such fixed interval resets said fixed fraction is added to said accumulator.

3. A system as claimed in claim 1 or 2, wherein means are provided for determining when the accumulator attains or exceeds a given count corresponding to a complete fare unit, and for then deducting that given count to leave zero or a remainder that contributes to a following accumulation, each complete fare unit so determined being registered elsewhere.

4. A fare accumulator system substantially as hereinbefore described with reference to Figs.

1, 2 and 3 or Figs. 1, 2 and 4 of the accompanying drawings.