FIELD OF THE INVENTION
The present invention relates to a digital slipmeter. More particularly, the invention is concerned about a micro-controller based digital slipmeter for use in tractors such that proper depth and gear throttle position can be set resulting in indication of instantaneous wheel slip and actual speed of the tractor and at the same time save fuel.
The invention finds its application in two wheeled drive tractors, four wheeled drive tractors and the like.
BACKGROUND AND THE PRIOR ART
During the field operation of tractors, a significant portion of the energy is lost in slippage of the traction wheels. In the absence of a slipmeter, operators are unable to set the control lever to maintain the desired slip of the tractor.
US 4517566 discloses the principle of ground speed measurement. Here Doppler radar sensor comprising an antenna reflector was used which reflects electromagnetic radiation emitted by an antenna feed of the sensor toward the ground at a slant angle and reflects radiation reflected from the ground back to the antenna feed, the improvement which comprises said reflector having a contour corresponding to a portion of an ellipse one focus of which is centered substantially at the point at which radiation

is emitted by the antenna feed and the other focus of which is substantially at the surface of the ground.
US 4441359 discloses a programmed digital computer which responds to outputs of measuring instruments for inspected engine, steering and braking responses of the automobile vehicles.
US 5058423 describes the method for checking the functioning of driving wheel slip control of automotive vehicles. It does not describe the methods for measuring the wheel slip. Though, the wheel slip of automobile vehicle is different from the off road vehicle (tractor).
US 5770998 discloses a device for displaying stationary/dynamic status of a car for assuring safety including a car stationary/dynamic state sensing part for detecting a change of speed of a predetermined time period sensed by a rotating slit plate mounted on a speed meter cable connecting device and a photo interrupter; a pulse generating part for converting an analog signal from the state sensing part into digital pulses and applying to a microcomputer;
The present invention deals with the methodology and constructional details of continuous wheel slip measuring and display on the tractor. The wheel slip of tractor in actual field condition varies from point to point due to variation in the soil condition. The tractive efficiency of the tractor is closely tied to wheel slip. Therefore, a continuous indication of slip is required to the operator

to avoid the excessive slip and hence to maintain the maximum achievable tractive efficiency.
Thus there is a need to provide for an apparatus or device for efficient indication of instantaneous wheel slip and actual speed of vehicle.
The present inventors have found that by means of micro controller based digital slip meter comprising encoder means wheel slip and actual speed of the vehicle can be determined instantaneously in correspondence with an appropriate number of pulses generated corresponding to the rotation of tractor wheel.
OBJECTS OF THE INVENTION
Thus, one object of the present invention is to overcome the drawbacks of the prior art.
Another object of the present invention is to provide a slipmeter for two-wheeled drive tractors, four wheeled drive tractors and the like.
Yet another object of the present invention is to provide a slipmeter which is micro controller-based digital slipmeter.

SUMMARY OF THE INVENTION
Accordingly, one aspect of the present invention is to provide a digital slipmeter for tractors comprising :
plural sensing means so as to measure rotational speed of wheels wherein said sensing means comprises transparent and/or semi transparent element so as to receive input pulses from rotation of wheel,
wherein said sensing means comprises detector means so as
to establish optical co-ordination with said transparent
and/or semi transparent element thereby generating an
output; and
micro controller unit being operatively connected to said sensing means so as to receive said outputs determine actual speed and wheel speed.
According to another aspect of the present invention there is provided a method for processing wheel slip and actual wheel speed of vehicles, said method comprising steps of :
receiving input pulses from rotating wheels, said pulses being received by plural sensing means comprising alternative transparent and/or opaque strips;
detecting alternative transparent and/or opaque strips by means of detector means so as to generate square wave inputs for processing; and

processing of said square wave input by means of micro controller unit whereby data information being processed so as to generate slip and actual speed of wheels.
The other objects and advantages of the present invention will be apparent from the description provided hereinbelow with reference to the accompanying figures and detailed description provided herein below.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a microcontroller-based digital slipmeter is developed which indicates the instantaneous wheel slip and actual speed of the tractor. It can be easily installed in the different make and model of tractors. This slipmeter is ideal for traction related R & D organizations as well as tractor manufactures.
The performance of this slip meter is independent of atmospheric conditions like temperature, humidity etc. This can also work in dusty environment and rainy condition.
This slip meter helps the operator to set the proper depth and gear-throttle position which would result in 15-20 percent fuel saving.
The cost of slipmeter is reimbursed within two years of the tractor use. The slipmeter is thus cost effective and could be adopted as an integral part of the Indian tractor.

In one embodiment of the invention, there are plural sensing means called encoders present in the said slipmeter. The sensing means comprises transparent and/or semi transparent element so as to receive input pulses from rotation of wheel.
The sensing means comprises detector means so as to establish optical co-ordination with said transparent and/or semi transparent element thereby generating an output.
A micro controller unit is operatively connected to said sensing means so as to receive said outputs to determine actual speed and wheel speed.
The sensor for measuring the rotational speed of the wheel is named as 'encoder'. An encoder consists of transparent disc, optical slot sensor, two ball bearings, shaft, water proof casing and signal output cable.Two encoders are used to measure the number of revolutions per minute (rpm) of both the rear wheels of the tractor. The average reading of two encoders with the multiplication of the distance traveled by rear wheel in one revolution on hard surface, gives the theoretical speed of the tractor. Similarly, an encoder measures rpm of the front wheel and the output of encoder with the multiplication of the distance travelled by the front wheel in one revolution on test surface give tractor's actual forward speed.
The pulse generated by the encoders of the two rear wheels (Er1 & Er2) and front wheel (Ef) is used to calculate the

slip by programmed micro-controller. The flowchart for calculating the slip is shown in Fig 5.
In another embodiment of the invention, a program is set in 8051 micro-controller which is implemented in the hardware components of the slipmeter to measure the instantaneous wheel slip and actual speed of the tractor. The functionalities and the module in which they are implemented are described in detailed circuit diagram shown in Fig. 4.
In another embodiment of the present invention there: is a method for processing wheel slip and actual wheel speed of vehicles. In this method input pulses are received from the rotating wheels by plural sensing means comprising alternative transparent and/or opaque strips. Alternative transparent and/or opaque strips are thereby detected by means of detector means so as to generate square wave outputs for processing. These square waves are processed by means of micro controller unit whereby data information is processed so as to generate slip and actual speed of wheels.
The alternating clear transparent and opaque stripes are placed at an angular separation of at least 4° to get 90 pulses in one rotation of the traction wheel.
An optical slot sensor is provided to detect the clear and opaque strip. The micro controller is programmed and implemented in hardware components of the slipmeter as detailed in figure 4.

Slip is not a directly measured value. It is calculated from two other measurements that are true vehicle forward speed and theoretical speed, which is being computed from the rotational speed and the rolling radius of the wheels.
The rear wheel rpm is measured for calculating the theoretical speed and front/fifth wheel is used to measure the true speed of the tractor.
The speed measuring device consists of a transparent disc with alternating clear and opaque stripes that are detected by optical sensor. The output of the optical sensors is fed to the timer port of the micro controller.
A micro controller program is written in Assembly language (X8051.EXE) to calculate number of revolution, Actual speed, Theoretical speed and finally wheel slip.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates a line diagram and component of encoder
Figure 2 illustrates clear and opaque disc used in the encoder.
Figure 3 illustrates installed encoders on a tractor.
Figure 4 illustrates detailed circuit diagram of the hardware with micro-controller.

Figure 5 illustrates flow chart for calculating the slip and actual speed.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In figure 1, the view of the encoder is shown. The encoder consists of transparent disc (1), optical slot sensor (2), two ball bearings (3), shaft (4), water-proof casing (5) and signal output cable (6).
In figure 2, the transparent disc is used which has alternating clear (7) and opaque stripes (8) at an angle of 4° to get 90 pulses in one rotation of the tractor wheel.
An optical slot sensor is provided to detect the clear and opaque strip. Due to the alternating clear and opaque strips a square wave is generated.
Figure 3 shows the installation of all the encoders on a tractor which is under field operation. The installation comprises Encoder on the right rear wheel (9), Connecting wire (10), Centre of the right rear wheel (11), Encoder on the front wheel (12), Connecting wire (13), Centre of the wheel (14), Encoder on the left rear wheel (15), Connecting wire (16), Centre of the left rear wheel (17).
Figure 4 gives a detailed circuit diagram of the hardware components of the slipmeter where the microcontroller is programmed and implemented in.

The outputs (i.e. square wave) of all the three encoders encoder 1 JP3, encoder 2 JP2 and encoder 3 JP1 are fed to the micro-controller which calculates the actual speed and wheel slip of the tractor. Two encoders are used to measure the number of revolutions per minute (rpm) of both the rear wheels of the tractor. JPl to JP3 are used for connecting the encoder. In encoder part optocoupler are used. When each black (8) and white track (7) of the encoder disk (as shown in figure 2) passes through optocoupler, a square wave pulse for each one white and black track is generated.
The continuous series of this pulse then goes through the IC741532 (18) . The raw pulse is not perfect square wave as per the shape and voltage. The square waves generated by the optocoupler are rectified through this IC as it acts as a Schmitt trigger.
The rectified square wave pulse is then read by the microcontroller (18). This pulse is processed by the microcontroller according to a given equation and result is displayed on the LCD. The 4049 here acts as a LCD driver. It also gives the computer output as a RS232 interface by using IC MAX 232. This IC is used as a level converter for computer interface.
The microcontroller also gives the signal to stepper motor for controlling the depth of implement.
IC 7805 is used as a voltage regulator to give perfect supply for microcontroller and others IC.

The structure thus conceived is adaptable to numerous modifications or variations. In practice the materials and dimensions may be dependant upon specific requirements and that will be comprised within its true spirit.

WE CLAIM
1. A digital slipmeter for tractors comprising :
plural sensing means so as to measure rotational speed of wheels wherein said sensing means comprises transparent and/or semi transparent element so as to receive input pulses from rotation of wheel
wherein said sensing means comprises detector means so as to establish optical co-ordination with said transparent and/or semi transparent element thereby generating an output; and
micro controller unit being operatively connected to said sensing means so as to receive said outputs determine actual speed and wheel speed.
2. Slipmeter as claimed in claim 1 wherein the sensing means comprises at least one encoder.
3. Slipmeter as claimed in claim 2 wherein the encoder further comprises ball bearings.
4. Slipmeter as claimed in claim 2 wherein the encoder is adapted to measure rpm of front wheel.
5. Slipmeter as claimed in claim 2 wherein the encoder is adapted to generate pulses from rear wheel speeds for wheel slip determination.

6. Slipmeter as claimed in claim 1 wherein the transparent and/or semi transparent element comprises at least one transparent disc.
7. Slipmeter as claimed in claim 6 wherein the transparent disc comprises alternative clear and opaque strips having mutual separation angle of at least 2°.
8. Slipmeter as claimed in claim 7 wherein the separation angle ranges from 2° to 4°.
9. Slipmeter as claimed in claim 1 wherein the detector element comprises at least one optical slot sensor adapted to detect clear and opaque strip of the transparent disc.
10. Slipmeter as claimed in any preceding claims wherein the micro controller is 8051 micro controller unit.
11. A method for processing wheel slip and actual wheel speed of vehicles, said method comprising steps of : receiving input pulses from rotating wheels, said pulses being received by plural sensing means comprising alternative transparent and/or opaque strips;
detecting alternative transparent and/or opaque strips by means of detector means so as to generate square wave inputs for processing; and

processing of said square wave input by means or micro controller unit whereby data information being processed so as to generate slip and actual speed of wheels.
12. The method as claimed in claim 11 wherein the alternative transparent and/or opaque strips are located at an angular separation of at least 4° from each other.
13. The method as claimed in claim 11 wherein the pulse generated by the sensing means of the wheels is adapted for determining the slip by programmed microcontroller.
14. A digital slipmeter for tractors as herein substantially described and illustrated with reference to the accompanying figures.

The present invention relates to a digital slipmeter for tractors. The slipmeter comprises plural sensing means so as to measure rotational speed of wheels. The sensing means comprises transparent and/or semi transparent element (1) for receiving input pulses from rotation of wheel, detector means (2) to establish optical co-ordination with the transparent and/or semi transparent element (1) thereby generating an output. The slipmeter further comprises micro controller unit (18) operatively connected to the sensing means to receive outputs determining actual speed and wheel speed. The invention also relates to a method for processing wheel slip and actual wheel speed of vehicles. The method steps comprises receiving input pulses from rotating wheels, detecting alternative transparent and/or opaque strips by means of detector means so as to generate square wave inputs for processing and processing of said square wave input by means of micro controller unit whereby data information being processed so as to generate slip and actual speed of wheels.