US 3376574 A
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A ril 2, 1968 w. R. F. GOSLING 3,376,574
. GUIDANCE SYSTEM FOR PLOUGHS Filed Jan. 24, 1967 TRANSMITTER I 16 RECEIVER 1 F United States Patent 3,376,574 GUIDANCE SYSTEM FOR PLOUGHS William Robert Frederic Gosling, Chalfont St. Peter, Buckinghamshire, England, assignor to The Rank Organisation Limited, London, England Filed Jan. 24, 1967, Ser. No. 611,382 3 Claims. (Cl. 343-107) ABSTRACT OF THE DISCLOSURE The disclosure describes an automatic control system for mole ploughs and trench diggers. A remote source transmits a reference beam of light which is received by a receiver. The receiver is mounted on the beam of a mole plough at a point intermediate the pivot end and the mole. The receiver emits signals which indicate the relative position of the receiver with respect to the reference beam and these signals are used to adjust the position of the pivot end of the mole beam. Disposition of the receiver intermediate the pivot end and the mole permits control of the degree of damping of the system.
This invention concerns automatically controlled machinery and has particular but not exclusive reference to automatically controlled ground working machinery such as mole ploughs and open trench diggers.
Machines of this kind normally have an implement which is constrained to move through the earth so as to dig a bore or a trench as may be required. For example mole ploughs have been used for some considerable time time as a method of providing cheap but not particularly durable drainage. More recently, however, new techniques have been developed in which a plastic strip is formed into a tube and laid into the mole drain as digging proceeds. This method of continuous laying allows relatively high digging rates, the full advantages of which can only be enjoyed if the grade or inclination of the drain so produced is maintained Within close limits at a set value.
According to the present invention there is provided an automatically guided machine having a guidance system which comprises output means for defining a point on the machine and indicating movement of said point with respect to a reference, and control means for controlling the position of said point in accordance with the output of the output means, the position of the point defined by the output means being selected to provide a required response in the control means.
The guidance system may comprise a transmitter for defining the reference and a receiver mounted at said point on the machine for defining misalignment of said point from the reference.
One embodiment of the invention will now be particularly described hereinafter by way of example and with reference to the accompanying drawing, which is a diagrammatic side view of an automatically guided mole plough.
The mole plough shown in the accompanying drawing comprises a beam 1 carrying at one end of a web 2 on which is mounted a mole 3, and the other end of which pivoted at 4 to a high powered tractor (not shown). The mole 3 digs a mole drain 5 as the plough is advanced, and suitable means (not shown) are provided for lining the mole drain 5 With a plastic tube (not shown) as digging proceeds.
The mole plough is provided with an automatic guidance system which can impose a predetermined inclination on the drain produced by the plough and which thus controls the depth of the mole 3 relative to a fixed datum. The automatic guidance system consists of two basic units, namely a transmitter 6 emitting a beam of light and defining a reference line and a receiver 7 in the path of the beam and defining a point on the mole beam 1. The output of the receiver 7 is arranged to be :a measure of its misalignment from the reference line defined by the transmitter 6 and this output is used to control the depth of the dig through a suitable servo-mechanism (not shown). A full description of this guidance system is given in application U.S. Serial No. 364,082, filed May 1,
The depth of dig is altered by changing the height of the pivot point 4 thus changing the inclination of the mole beam 1, and causing the mole 3 to take up its required position. The actual height of the pivot point 4 is controlled by a hydraulic piston-and-cylinder arrangement generally indicated at 8. Supply of pressure fluid to the cylinder is controlled by a valve (not shown) in turn controlled by the output of the receiver 7. However, when the reeciver 7 is placed at what seems to be the most natural position, that is close to the mole 3, it has been discovered that the result is at best an extremely underdamped system and at the worst an unstable system. There is thus a very strong possibility that under such conditions the guidance system would not work correctly and would be considered by a user to be completely useless.
The reasons for this are as follows:
It has been established that a mole will always move in the direction of its axis. Utilising this fact it is possible to describe its dynamic behaviour mathematically and to derve an open loop transfer function for a mole plough which relates the movement Yp of the ploughs pivot to the movement Y of a point on the beam. The transfer function is:
Y s+l Yp $s+l where sis the Laplace variable In considering movement (Ym) of the mole, 11:0 and the Equation 1 simplifies to:
From the equation it will be seen that the effect of having a long mole beam and thus making the time constant L/ V as large as possible is to make Ym insensitive to Yp. The length of the beam also affects the distribution of forces on the mole. The longer the beam the smaller its inclination to the horizontal and the smaller the vertical component of the force acting on the mole. It will thus be seem that the feature of having a long beam prevents the undulations of the surface from be ing transferred to the mole drain. Thus given a piece of land which is known to have a natural fall a nonautomatically guided plough could be relied upon to dig a drain reasonably parallel with that fall yet without excessive undulation. In an alternative form of mole plough (not shown) the mole is pivoted to the mole beam so that the inclination of the drain dug by the mole plough depends on the angle between the mole and the mole beam. However, for the purposes of this invention and description, such a plough functions identically to, and encounters the same problems as the mole plough shown in the accompanying drawing.
However with an automatically guided plough, which can be used in land which does not have a natural fall, the effect of making Ym insensitive to Yp creates the hereinbefore mentioned difficulties in the guidance system.
It has been discovered, and this is an extremely important feature of this invention, that the guidance system can be satisfactorily stabilized by selecting the position of the receiver 7 on the mole beam 1. The effect of this chosen position is to give a value to the integer a in Equation 1 which gives the guidance system the required response.
Naturally the value of a will be selected in accordance with the degree of damping required in the control of the plough and this will vary with particular circumstances. However the response of the control system can be methematically defined by the equation:
Ld Y dv ad Yt dYt i- (V-i' f) +f 1/ 'r-lwhere f is the ratio of the vertical component of the velocity of the pivot point 4 relative to the tractor to the misalignment of the receiver 7 from the reference defined by the transmitter 6, and Y is the movement of the tractor in the vertical plane.
Variations of the equation can be used in determining the value of a in automatically guided machinery other than mole ploughs. For example, when using the guidance system hereinbefore described with the well known kind of open trench digger which uses a ro-table shoe, the response of the control system can be mathematically defined by the equation:
2 2 v+aKL %+vKLY= Z- where k is the ratio of the angular velocity of the shoe relative to the beam, to misalignment of receiver from the reference line.
It will be seen that this invention provides a way in which a difficult problem encountered in automatically guided machinery is solved by an entirely new approach.
It could, of course, be possible to solve the problem by purely electronic means, and this would seem to be the most natural course for a person tackling the problem to follow. However, such a solution would be expensive and complicated.
This invention overcomes the problem by a consideration of the geometry of the factors involved. Such an approach can be applied in a wide variety of ways. For example instead of using the guidance system to control vertical movement of a plough or digger, it could be used to control horizontal movement, that is to steer a machine. In such a case the basic equation would vary, but the actual approach to the problem would be the same. Similarly, the invention could be used in controlling both the steering and the vertical movement of a machine.
This invention is not necessarily limited to optical guidance systems, as similar problems would arise in radar or other guidance systems.
1. An automatically guided digging device of the type adapted to be moved in a forward direction by a vehicle and comprising:
an elongated element having a pivot means at one end thereof, said elongated element having an axis extending in the direction of movement;
digging means attached to said elongated element at the end opposite said pivot means;
a remote transmitter for transmitting a reference beam;
a receiver means for receiving said reference beam and producing output signals indicative of the relative position of said receiver means with respect to said reference beam; and
control means responsive to said output signals for moving said pivot means in a vertical plane to shift the position of said elongated element thereby maintaining said receiver means in a position to receive said reference beam;
said receiver means being movably mounted on the axis of said elongated member for movement along said axis to fixed positions at points intermediate said pivot and said digging means so that the degree of damping in the control of said digging means can be varied as required by the terrain being dug by said digging means.
2. An automatically guided digging device as claimed in claim 1 wherein said digging means is a mole plow.
3. An automatically guided digging device as claimed in claim 1 wherein said remote transmitter comprises a light source for transmitting light as said reference beam.
References Cited UNITED STATES PATENTS 3,000,121 9/1961 Martin et a1. 3,009,271 11/ 1961 Kuehne et a1. 3,242,340 3/ 1966 Layne. 3,314,068 4/ 1967 Verive 343-107 RODNEY D. BENNETT, Primary Examiner.
H. C. WAMSLEY, Assistant Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,376 ,574 April 2 1968 William Robert Frederic Gosling It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 1, line 60, cancel "of". Column 2, line 31, "derve" should read derive same column 2, lines 35 to 39, the equation should appear as shown below:
V Column 3, lines 18 to 20, the equation should appear as shown below:
same column 3, lines 33 and 34, the equation should appear as shown below:
Ld (v aKL) dz VKLY ad t v d t Signed and sealed this 11th day of November 1969.
EDWARD M.FLETCHER,JR. WILLIAM E. Attesting Officer Commissioner of Patents SCHUYLER, JR.