MEANS FOR DETERMINING DISTANCE BETWEEN TWO POINTS

Abstract: A means for determining the distance between two spaced points, such as ground surface and a tip of a ground working tool of an agricultural machine, comprising transmitting and receiving means (13, 15) adapted for positioning at a location remote from the two points, and means (27) for generating a first timing signal equal to the time a pulse emitted by the transmitting means (13) takes to be reflected from one of said two points and received by the receiving means (15). There is provided a means (25) for generating a reference timing signal representative of the time the pulse would take to be reflected from the other of said two points and received. A gate means (29) is provided for deriving a differential timing signal equal to the time difference between the first timing signal and the reference timing signal. The differential timing signal is converted by a converting means (37, 39, 41) into an output signal representative of the spacing between the first and second points. ing between the first and second points.) for generating a first

Description: "Means for Determining Distance Between Two Points" THIS INVENTION relates to means for determining the. distance between two spaced points. The invention has been devised particularly, although not solely, for use in monitoring the position of a ground working tool of an agricultural machine relative to the ground, so as to provide an indication of the working depth of the ground working tool and/or to actuate a control system for controlling the working depth. In one form the invention resides in means for determining the distance between two spaced points comprising: trans¬ it) itting and receiving means adapted for positioning at a location remote from the two points, means for generating a first timing signal : proportional to the time for a signal transmitted by the transmitting and receiving means to be reflected from one of said two points and received by the -transmitting and receiving means, means for generating a reference timing signal representative of the time for a signal transmitted by the transmitting and receiving means to be reflected from the other of said two points and re- . ceived by the transmitting and receiving means, counter 20 means for generating a differential timing signal pro¬ portional to the time difference between the first timing signal and the reference timing signal, and converting means for converting the differential timing signal to an output signal representative of the spacing between the first and second . points. The transmitting and receiving means may comprise a trans¬ mitter and a receiver. Alternatively, the transmitting and receiving means may comprise a transceiver. In one arrangement, display means may be provided for pro- 30 viding a visual display representative of the distance between the two spaced points. In another arrangement, the output signal may be compared with a further signal repre¬ sentative of a predetermined spacing between the two points, and means provided for generating a differential signal sentative of the difference between the output signal and said further signal. The differential signal may operate an automatic control system for controlling the distance bet¬ ween the two points. The means for generating the reference timing signal may comprise a monostable multivibrator adapted to receive a triggering signal from triggering means for the transmission mode of the transmitting and receiving means, said reference timing signal corresponding to the time during which the onotstable multivibrator remains in its unstable state. The counter means may comprise a logic gate one logic level output of which constitutes said differential timing signal. The converting means " may comprise a constant voltage source coupled to an integrator through a switch, the switch being rendered conductive by the presence of said one logic level at the output of the logic gate. A filtering means is preferably provided to permit the counter means to respond only to the first signal reflected from said one point and not reverberations of the first signal. The filtering means may comprise a bistable multivibrator wherein the outputs of the receiver mode of the transmitting and receiving means and the monostable mulitvibrator are fed to a logic circuit which in turn is connected to a first input of the bistable multivabrator and the output of the triggering means is connected to a second input of the bistable multivibrator, whereby the bistable multivibrator sets its output signal in a first stable state if an output signal from the receiver mode of the transmitting and re¬ ceiving means is first received during the period in which OMFI_ the monostable multivibrator is in its unstable atate or sets its output signal in a second stable state if a trig¬ gering signal is received, the output signal of the bistable multivibrator being utilised in conjunction with the output signal of the monostable multivibrator to provide control of the counter means ' and converter means. Resetting means are provided for resetting the integrator to zero in circumstances where the monostable multivibrator is in its unstable state and the bistable multivibrator is in its said other stable state. Latch means may be provided for latching the output of the integrator to the output of the converting means when the monostable multivibrator is in its stable state and the bistable multivibrator is .in its said one stable state. In another form, the invention resides in means for deter¬ mining the position of a ground working tool of an agri¬ cultural machine relative to the ground surface, comprising: transmitting and receiving means adapted for mounting on the agricultural machine, means for generating a first timing signal proportional to the time for a signal transmitted by the transmitting and receiving means to be reflected from the ground surface and received by the transmitting and receiving means, means for generating a reference timing signal representative of the time for a signal transmitted by the transmitting and receiving means to be reflected from a predetermined portion of the ground working tool and received by the transmitting and receiving means, counter means for generating a differential timing signal pro¬ portional to the time difference between the first timing signal and the reference timing singal, and converting means for the converting the differential timing signal to an output signal representative of the spacing between said portion of the ground working tool and the ground surface. OMPI The transmitting and receiving means is preferably mounted on the upper end portion of the ground working tool. The invention will be better understood by reference to the following description of one specific embodiment thereof as shown in the accompanying drawings in which: Figure 1 is a schematic circuit diagram of distance measuring means according to the invention; and Figure 2 is a timing diagram for the circuit of figure 1. The embodiment shown, in the drawings is directed to means for determining the • istance between the lowermost point of one or more ground working 'tools of an agricultural machine and ground -surface so as to ■ provide an indication of the depth of penetration of the ground working tool. In the embodiment, the ground working tools are in the form of tynes on the lower end of which are mounted agricultural points. A transducer mount (not shown) is provided for mounting a transmitter 13 and a receiver 15 on the upper end of each of number of selected tynes. Each transducer mount is posi¬ tioned so that the transmitter and the receiver are directed towards the agricultural point at the lower end of the respective tyne whereby the receiver is able to receive the echoes of pulses transmitted by the transmitter and reflect¬ ed from ground surface. Each transmitter and its associated receiver are mounted on the resepctive tyne, rather than on a fixed part of the agricultural machine, so as to permit the transmitter and the receiver to move with the tyne; this has the effect of reducing the cosine error which arises on rotation of the tyne in comparison to that which would be produced on rot- O PI ation of the tyne if the transmitter and receiver were mounted on a fixed part on the agricultrual machine. The cosine error arises because rotation of the tyne effectively reduces the vertical distance between the frame of the agricultural machine and the tip of the agricultural point carried by the tyne. Associated with each transmitter 13 is a transmitter drive 17 which is adapted to provide a conditioned triggering pulse from a trigger generator 19 to the transmitter 13. The trigger generator 19 is arranged to generate a "transmit enable" pulse which in this embodiment is of 0.5 mS duration every 20 mS. The transmitter is triggered by the "transmit enable" pulse and transmits a pulse of sound at a frequency of about 40 kHz for the duration of the triggering pulse. The output of the receiver 15 is coupled to one input of a first logic gate 21 through a receiver amplifier 23. The output of the receiver amplifier 23 is a logic level which is low during transmission by the transmitter and also when the receiver is receiving a sufficiently strong echo. In other circumstances, the output of the receiver amplifier is a logic level which is high. The input of a monostable multivibrator 25 is coupled to the trigger generator 19 whereby the monostable multivibrator is triggered by the end of the "transmit enable!' pulse. The monostable multivibrator is arranged to remain high for the time that it would take for sound to travel from the trans¬ mitter to the tip of the agricultural point of the tyne and back to the receiver, typically about 3 mS. The output of the monotstable multivibrator is coupled to the second input of the logic gate 21 the output of which is coupled to a bistable multivibrator 27. The bistable multivibrator is adapted to be set high by the receiver output signal fal¬ ling, but only if the output of the monostable multivibrator is high; in this way, the bistable multivibrator is set high __QMPI only by the echo pulse, and not the transmit pulse. The output of the bistable multivibrator 27 remains high until reset by the next "transmit enable" pulse (as shown in the timing diagram of figure 2), so it is not effected by echoes other than the first. Three other signals are derived from the outputs of the monostable multivibrator and the bistable multivibrator; these signals are referred as "reset", "count" and "latch" respectively and are shown in the timing diagram of figure 2. More particularly, the count signal is defined by a logic level which is high at the output of a logic gate 29 (hereinafter referred to as the "count logic gate") the inputs of which are coupled respectively to the monostable multivibrator and.the bistable multivibrator. The output of ' the count logic gate is at a logic level which is high and the output of the monostable multivibrator is high and the output of the bistable multivibrator is also high. The reset pulse is defined by a logic level which is high at the output of a logic gate 31 (hereinafter referred to as the "reset logic gate"). The two inputs of. the reset logic gates are coupled to the monostable multivibrator and the bistable multivibrator respectively. The output of the reset logic gate 31 is set at a logic level which is high when the output of the monstable multivibrator is high and the output of the bistable multivibrator is. low. A logic level which is high at the output of a logic gate 33 (here¬ inafter referred to as the "latch logic gate") defines the latch pulse. As with the count logic gate and the reset logic gate, the inputs of the latch logic gate 33 are coupl- ed to the outputs of the monostable multivibrator and the bistable multivibrator respectively. However, the output of the latch logic gate is set at a logic level which is high when the output of the monostable multivibrator is low and the output of the bistable multivibrator is high. G..IPI A constant voltage source 37 is coupled to one input of an integrator 39 through a switch 41. When a count pulse is present, the switch 41 is rendered conductive and a constant voltage is applied to the input of the integrator 39, so that at the end of the count pulse the integrator output voltage is a measure of the length of the count pulse and hence is representative of the tyne depth. A second switch 43 is adapted to latch the output voltage of the integrator through to display circuitry (shown generally at 45) via a resistor 47 and selector switch 48. The second switch 43 is rendered conductive when a latch pulse is present. A third switch 49 is incorporated in the feed back network of the integrator 39. Operation of the third switch 49 is con¬ trolled by the reset logic gate 31 whereby the switch is rendered non-conductive when a reset pulse is present so as to reset the integrator to zero. In order to indicate whether or not echoes being received by the receiver are adequate, the output of the bistable multi¬ vibrator 27 is low pass filtered and applied to a comparitor which in turn drives a light emitting diode 51 in such a way that the diode lights when the echo return rate is satis¬ factory. Each transmitter and receiver pair has the circuitry desc¬ ribed above. In each case, the output voltage of the in¬ tegrator is taken via the respective selector switch 48 to a common capacitor 53 in the display circuitry 45, so that a user can select any one, or any combination of, transmitter and receiver pairs. If only one transmitter and receiver pair is selected and working, the capacitor 53 will charge upto the output voltage of the corresponding integrator 39 and the display will show the corresponding tyne depth. If more than one transmitter and receiver pair is selected and working, the voltage will be the average of the respective integrator output voltages, and the display will show the / OΪ.-PI - 8 - average depth. The charging time constant for the capacitor is long enough to filter out short term fluctuations and show a short time average. If none of the transmitter and receiver pairs are giving a signal, the capacitor will discharge at a very slow rate only, thereby holding the current reading for a short time. The voltage on the common capacitor 53 is applied to one input of an adder 55 the other input of which is coupled to a signal generator 57 which is adapted to generate a signal proportional to the desired depth of the tyne. The output of the adder 55 is coupled to a bar display 59 which pro¬ vides a visual display representative of the position of the tyne relative to the ground surface. The velocity of sound in air varies according to ambient temperature and to compensate for this, temperature sensi¬ tive components are used to adjust the period of the mono¬ stable multivibrator. An automatic control system (not shown) may be provided for actuating a control mechanism which adjusts the working depth of the tynes to compensate for variations from the desired depth setting. In one arrangement, the control system may be arranged to respond to logic signals taken directly from a bar display which provides a .visual indic¬ ation of the position of the tyne with respect to the desir¬ ed depth setting. In operation, the trigger generater 19 generators a "trans¬ mit enable" pulse of 0.5 mS duration every 20 mS. The "transmit enable" pulse is applied to the driver 17 of each transmitter 13 and to the monostable multivibrator and bistable multivibrator corresponding to each transmitter, the monostable multivibrator 25 is triggered by the end of the "transmit enable" pulse and remains high (i.e. in its _OM?I unstable state) for the time that it would take for sound to travel from the tramsitter to the tip of the tyne and back to the receiver (typically 3 mS) . The high at the output of the monostable multivibrator is a reference timing signal. The output of the bistable multivibrator 27 is set to a high logic level by the receiver output signal falling, but only if the output of the monostable multivibrator is high. When the outputs from both the monostable multivibrator and the bistable multivibrator are high, the count logic gate 29 has a logic level which is high at its output and this renders the switch 41 conductive so as to apply a constant voltage to the integrator 39. When the monostable multivibrator returns to its stable state, the logic level at the output of the count logic gate 29 changes to a low thereby termin¬ ating the count pulse. At the end of the count pulse, the output voltage of -the integrator 39 gives a measure of the length of the count pulse which is proportional to the depth of the respective tyne. The output voltage of the integ¬ rator is latched through to the display circuitry 45 when a latch pulse is present (i.e. when the output of the latch logic gate 33 is at a logic level which is high). The output voltage of the integrator is applied to the capacitor 53 and in circumstances where only one transducer is sel¬ ected and working, the capacitor will charge up to the voltage of the integrator and the display will show the corresponding tyne depth. On the other hand, if. more the one transmitter and receiver pair are selected and working, the voltage across the capacitor will be the average of the various integrator outputs, and the display will show the average depth of the respective tynes. The adder 55 sub¬ tracts the voltage on the capacitor 53 from a voltage gener¬ ated by the signal generator 57, which is representative of the desired depth setting, and the output is displayed at the display bar 59. It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described. For example, the invention is not limited in application to monitoring of the working depth of one or more ground work¬ ing tools of an agricultural machine, and may be applied to other suitable situations where it is necessary to monitor the distance between two points at least one of which is movable relative to the other.

Claims: " 1 - THE CLAIMS defining the invention are as follows:- 1. Means for .determining the distance between two spaced points comprising: transmitting and receiving means adapted for positioning at a location remote from the two points, means for generating a first timing signal proportional to the time for a signal transmitted by the transmitting and receiving means to be reflected from one of said two points and received by the transmitting and receiving means, means for generating a reference timing signal representative of the time for a signal transmitted by the transmitting and receiving means to be reflected from the other of said two points and received by the transmitting and receiving means, counter means for generating a differential timing signal proportional to the time difference between the first timing signal and the reference timing signal, and .converting means for converting the differential timing signal to an output signal representative of the spacing between the first and second points. 2. Means as claimed in claim 1 wherein there is provided a display means responsive to said output signal for providing a visual display representative of the distance between the two spaced points. 3. Means as claimed in claim 1 including comparator means for comparing the output signal with a further signal repre¬ sentative of. a predetermined spacing between the two points, and means for generating a differential signal represent¬ ative of the difference between the output signal -and said further signal. 4. Means as claimed in any one of the preceding claims wherein the means for generating the reference timing signal comprises a monostable multivibrator adapted to receive a triggering signal from triggering means for the transmission mode of the transmitting and receiving means, said reference timing signal corresponding to the time during which the monostable multivibrator remains in its unstable state. 5. Means as claimed in any one of the preceding claims wherein the counter means comprises a logic gate one logic level output of which constitutes said differential timing signal . 6. Means as claimed in any one of the preceding claims wherein the converting means comprises a constant voltage source coupled to an integrator through a switch, the switch being rendered conductive by the presence of said one logic level at the output of the logic gate. 7. Means as claimed in any one of the preceding ' claims wherein the filter means comprises a bistable multivibrator wherein the outputs of the receiver mode of the transmitting and receiving means and the monostable multivibrator are fed to a logic circuit which in turn is connected to a first input of the bistable multivibrator and the output of the triggering means • is connected to a second input of the bistable multivibrator, whereby the bistable multivibrator sets its output signal in a first stable state if an output signal from the receiver mode of the transmitting and re¬ ceiving means is first received during the period in which the monostable multivibrator is in its unstable state or sets its output signal in a second stable state if a trig¬ gering signal is received, the output signal of the bistable multivibrator being utilised in conjunction with the output signal of the monostable multivibrator to provide control of the counter means and the converter means . 8. Means as claimed in claim 6 or 7 including resetting means for resetting the integrator to zero in circumstances where the monostable multivibrator is in its unstable state OMPI and the bistable multivibrator is in its said other stable state. 9. Means as claimed in claim 6, 7 or 8 wherein latch means may be provided for latching the output of the integrator to the output of the converting means when the monostable multivibrator is in its stable state and the bistable multi¬ vibrator is in its said one stable state. 10. Means for determining the position of a ground working tool of an agricultural machine relative to the ground surface, comprising: transmitting and receiving means adapt¬ ed for mounting on the agricultural machine, means for generating a first timing signal proportional to the time for a signal transmitted by the transmitting and receiving means to be reflected from the ground surface and received by the transmitting and receiving means, means for generat¬ ing a reference timin'g signal representative of the time for a signal transmitted by the transmitting and receiving means to be reflected from a predetermined portion of the ground working tool and received by the transmitting and receiving means, counter means for generating a differential timing signal proportional to the time difference between the first timing signal and the reference timing signal, and con¬ verting means for converting the differential timing signal to an output signal representative of the spacing between said portion of the ground working tool and the ground surface. 11. Means as claimed in claim 10 wherein the transmitting and receiving means is mounted on the upper end portion of * the ground working tool . 12. Means substantially as herein described with reference to the accompanying drawings.

Inventors: MILLS DAVID JOHN, RICHTER ALAN STANLEY, MILLS, DAVID, JOHN, RICHTER, ALAN, STANLEY
Applicants: AGTRONICS PTY LTD, AGTRONICS PTY. LTD.
Application year: 1984
Main classification: G01S15
IPC codes: A01B63, G01S15