ES2267320A1 - Portable penetrometer for agricultural use for measuring compaction and resistance of ground has electronic circuit that processes signals from load cell and optical encoder and stores signals for uploading in computer - Google Patents

Abstract

A commercial load cell determines the resistance to penetration by the ground and emits a corresponding electrical signal, and measures the depth during ground penetration. An optical encoder counts the number of turns of the screw nut from the start of operation. Signals from the load cell and optical encoder are processed by an electronic circuit controlled by a reduced instruction set computer (RISC) microcontroller. The signals are stored for uploading in a computer executing software for obtaining curves relating cone index and depth and the characteristics of tests. A conical end penetrates the ground at a constant speed of 3 centimeters per second. A small screw nut is driven to rotate by an electric battery motor like a drill used in carpentry or do-it-yourself jobs.

Description

Portable penetrometer with spindle mechanism, for agricultural uses, managed with microcontroller and computer.

Object of the invention

It is a prototype penetrometer or apparatus used to measure the degree of compaction and resistance of soil for agricultural purposes. The device must push to a point standard conical that penetrates the ground at a constant speed of 3 cm / s. The prototype has the character of being portable and manageable at the plot level by a single operator and use as principle of displacement of said conical tip a mechanism Spindle (Screw-nut) of known pitch, which it is rotated with a battery powered electric motor such as called "drills" or "tops" used in carpentry or  DIY As a resistance element offered by the soil when being penetrated uses a commercial load cell that emits an electrical signal proportional to that force and as an element which measures the depth at which the tip during its trajectory a device called optical encoder (Encoder) that counts the turns turned by the screw from the beginning of the operation. The two signals, the from the load cell and that of the Encoder, are properly treated in an electronic circuit controlled by a RISC architecture microcontroller as an essential element of the same. The two signals are stored and finally they can be dump a computer having developed a Software that allows to obtain curves of (Cone Index) - (Depth), characteristics of these tests.

State of the art

Penetrometers are devices that allow determine the resistance to soil penetration, which is the force (force per unit area) needed to enter a conical tip to a certain depth in the profile of the ground. The Cone Index at a given soil depth is the average penetration resistance value found up to such depth. It is usually expressed in kPa or MPa and being variable with depth, it is usual to represent the results in graphic form IC-Prof.

Due to its simplicity, the penetrometer technique has been widely used in soil characterization studies through its mechanical properties and properties related to its state and nature, in its natural state
(Bekker, 1969; Yong et al. , 1984; Wong et al. , 1991). Maclaurin (1987) and Okello (1991) consider the penetrometer together with the bevmeter as the most appropriate techniques for determining soil properties in studies of extra-locomotion locomotion.

The penetrometer technique is quite fast and easy to make, finding numerous applications, such as, soil characterization for passability studies of vehicles, quantify soil compaction variations, and studies of the physical opposition of the soil to the development of the system Root of plants.

The penetrometers described in the literature can be divided into 3 groups, depending on the drive system, these are: manual, electric and hydraulic
Licos.

In the first, it is the operator that uses its force to push the rod-cone system through two handles, trying to keep the speed of penetration, or, drops a known mass from a certain height in impact penetrometers.

The hydraulic or electric drive They are usually transported on a tractor or similar machine, that receives the necessary energy, either by the hydraulic sockets, PTO or its electrical circuit. They have the advantage over the manuals, of not requiring physical effort of the operator, which allows to carry out numerous tests on hard floors, in a short space of time. On the contrary they have the disadvantage of their difficulties in accessing certain places due to the tractor that they transport them, either for the destruction of the crop that it it would mean, either because of the topography of the land.

Regarding the measurement system and registration of data, there is an extensive range, both manual and automatic. In those of manual registration, use a dynamometric ring whose deformation is read and noted at depth intervals constant by the operator. In automatic registration they are used generally force or pressure transducers whose output, properly conditioned, it attacks the registration unit that can be graphic or numerical type, in the latter, digital equipment.

The widespread use of penetrometers made precise their classification, in order to compare the measures taken by researchers around the world. Thus, the American Society of Agricultural Engineers (A.S.A.E.) typified the penetration resistance test in the standard S313.1 (A.S.A.E. Standard, 1980). Currently the current standard is the  S313.3 (A.S.A.E. Standard, 1999).

In the bibliography it is described numerous penetrometers adapted to the A.S.A.E. but what do I know difference in aspects not included in it, fit highlight:

As a manually operated penetrometer and numerical register, those of Wells et al. (1981), O'Sullivan et al. (1983) and Woosruff and Lenker (1984). In them the readings were made at intervals of constant depth and were collected in a digital data acquisition system, stored on magnetic tapes or in electronic memories
cas.

Riethmuller et al. (1983) develop a hydraulic drive penetrometer with a measurement system based on a microcomputer, the tractor supports the 3 m long frame through which a 60 cm hydraulic cylinder travels. It used an extensometric force transducer and two potentiometers for lateral displacement of cylinder and vertical plunger. The three analog signals were transformed into variable frequency signals, being collected by the microcomputer for measurement and recording on magnetic tape. The data had an output written in a printer attached to the microcomputer.

Agüera et al. (1991), he designed, a manually operated portable penetrometer, which had a force meter and a displacement meter, which allowed the data to be stored on a portable PC and simultaneously visualized the test, the IC-depth curve on its screen.

The possibility of access with the penetrometer to any point of the plot in diverse cultivation conditions makes the portable penetrometers they use interesting the strength of the operator itself, but it has limitations: not being able exceed penetration resistance higher than effort that an operator can manually supply, this is 3 MPa, inability to maintain penetration speed constants when there are significant variations of resistance and not be able to perform numerous repetitions due to physical exhaustion of operator.

That is why it would be of interest to have of a portable penetrometer, manageable by a single operator and easy to operate in the field, that do not present the limitations derived from manual actuation, which allows us to register a large number of essays and the possibility to show the graph IC-Depth simultaneously to the test.

The device that has been designed and built It requires only one operator, it is easy to handle at the plot level and It is powered by a DC electric motor. Through it the constant penetration speed is ensured, essential parameter for the correct determination of the Index of Cone. Through two sensors, an optical encoder and a cell load, the displacement of the stem will be measured at every moment and the force necessary to penetrate said stem into the ground. May measure penetration resistance up to 7.5 MPa if handled by a single operator and up to 15 MPa if you have the help of a  second person. All the electronic equipment and the software necessary for the measurement, recording and analysis of the penetration resistance test information allowing store a large number of trials and the ability to show the IC-Depth graph simultaneously to the test with  The use of a portable PC. An essential feature of equipment is its electric drive even being a machine laptop.

Description of the figures

Figure one

General view of the mechanical structure of the equipment

The support column (1) can be seen in the figure solidarity with a square base (4) that has legs in the form of claws (3). The mechanism assembly is attached to this column spindle nut (17) by means of a coupling system (fifteen).

This mechanism serves as support for following elements that can be seen in the figure: support plate the circuit box (14), the circuit box itself (9), the battery holder (8), the batteries themselves (18), the plate to fix the load cell (7) and the load cell itself (6) which is responsible for measuring the resistance to penetration of the rod-cone assembly (5).

In the upper part of the team two are appreciated equal gears of 28 teeth. One is spindle gear (13) which has an engine coupling in its center impeller (12), which rotates the encoder gear (11) dragging the axis of the optical encoder (10), which is responsible for measuring the depth of penetration automatically.

The rod-cone assembly (5) part of the load cell (6), crosses the plate through a hole of the support (3). In its displacement when making measurements, the stem is guided by a guide (2) that goes placed in the support column.

The equipment to be transported has a handle for transport (16).

Figure 2

Support detail and support base

It is a support column (1) formed by a hollow steel profile, with a square section of 40 x 40 mm section, 90 cm high welded to a base or steel plate of 40 x 40 cm and 3 mm thick (4), in which legs are incorporated in shape of ground fixing claws (3). This column is attach a rod guide (2) that travels through it, fixing its position at will. This guide has a hole through which the stem circulates to correctly guide your address.

Figure 3

External view of nut-spindle mechanism

The nut-spindle mechanism (17) is formed by a 40 x 40 mm outer quadrangular tube, equipped with platforms for the circuit box (14) and another for the batteries (8). The hitch to the column is also appreciated support (15) welded to I mentioned outer tube, equipped with two screws with dome heads to fix it to the column support of figure 2; on the right side you see a handle for the transport of the equipment (16).

At the upper end of the 40 x 40 mm tube, the spindle gear of 28 teeth is appreciated. The center of rotation of this gear matches the geometric axis of the tube quadrangular is integral with the screw of the spindle mechanism (Figure 4), which is inside the outer quadrangular tube. This gear has a quick coupling of the drive motor (12). Furthermore said gear transmits the movement to the gear of the encoder, which rotates the encoder shaft.

Figure 4

Detail of the screw-spindle stem and its nut inside the outer quadrangular tube

In the spindle mechanism (17) the nut (19) to which the telescopic inner tube (21) is welded quadrangular shape of 36 x 36 mm section. When moving the nut when turning the spindle (20), telescopically displaces the inner tube (21) at whose lower end it carries the support plate of the load cell (7) and the load cell itself (6) to which the rod-cone assembly is coupled.

Figure 5

Electronic sensors and conditioners

You can see the sensors (sensors) and conditioners used in the electronic design of the equipment as well as your disposition The sensors (load cell and encoder) they emit electrical signals that will be prepared by the conditioners, being processed by a laptop (PC)

Description of the invention

It's about the design of a portable penetrometer (figure 1), to prospect up to 50 cm deep, to be managed by a single operator, in which the energy needed to penetration is obtained from an electric current motor continues to be battery powered, just like the current "tops" or drills for use in DIY or similar, without connection to the network.

The penetrometer consists of three parts fundamental:

A mechanical part or support structure of the nut / spindle system and mechanism, electronic sensors and conditioners to measure efforts, forward speed of the conical tip and position at each instant and finally, the dump and information processing software.

1. Support structure and spindle mechanism

The support structure is a hollow tubular steel profile, 40 mm in section by way of a shaft or a 90 cm high column that rests on the ground by means of a 40 x 40 cm base plate (figure 2). Attached to this shaft and being able to choose different positions, the spindle mechanism is coupled (figures 3 and 4), which in turn consists of two hollow tubes, with quadrangular and concentric sections, being able to move longitudinally inside each other. The screw or spindle has a length of 50 cm and a helical pitch (p) of 0.5 cm / turn, runs longitudinally through the inside of the outer tube and supports at the upper end of it in an axial bearing that closes to this tube , a quick coupling of the drive motor emerging to the outside. The nut of the screw (spindle), is in solidarity with the inner concentric tube, in such a way that when the screw is rotated and the nut being the movable part it moves through the inside of the larger diameter tube by dragging the smaller diameter tube, which moves telescopically up or down according to the direction of rotation of the
engine.

2. Electronic sensors and conditioners of signals

The mobile inner tube has at its base a load cell, equipped with strain gauges, which works at 250 kg traction-compression and a full scale 3000 divisions and 2 mV / V configured in Wheastone bridge complete, to which the rod equipped with the conical tip is threaded. These gauges provide electrical signals proportional to the forces that are exerted when the conical tip penetrates into soil. The value of each of these forces split by the cone base section of the conical tip mentioned above gives the Cone Index.

Said electrical signal passes through a conditioner responsible for amplifying the differential output of the bridge Wheastone and feed the load cell with a voltage of 10 V. An analog / digital converter is then used (MAX-186), 12-bit resolution on a background of scale, which for this application, has been set by a 4096 mV internal reference, which means that each step of the Converter is a millivolt.

Also to measure the position of the tip With respect to the soil surface, it is done by counting of the number of turns the screw has turned from a situation initial nut. The number of laps multiplied by the step of the spindle (p = 0.5 cm), gives the position. This operation is performed. using an optical encoder (Optical encoder model 360 P / W ¼ '' S), with two digital outputs 90º out of phase, which allows Determine the direction of rotation of the spindle.

For encoder management a PIC microcontroller 16F84-A / 20, which using the interruptions due to change of state of the corresponding pins to the high nibble of port B of this device. For one Efficient communication with the PC, has been selected capable of perform 5 million instructions per second (crystal of 20 MHz)

The penetrometer connection to the PC makes it a through the parallel port, as this has a large number of lines, which make communication more efficient.

The arrangement of the collectors and conditioners are shown in figure 5.

The control of the speed of advance of the tip it is done maintaining the speed of rotation approximately constant, providing greater or lesser current intensity to the observe a dial that will mark the tendency to lower or raise it turning speed when the torque increases or decreases respectively resistant to penetrate the tip.

3. Dump and processing software information

Two programs have been developed:

a.- Program for the control device programmable, in assembly language, based on an attached routine to the hardware interrupt service.

b.- Control, visualization and registration of the tests, in Visual Basic, whose functions are, link by using a DLL, the PC with the penetrometer, Performs the communication protocol, with the A / D converter, allows to obtain position data (depth), processed by the microcontroller and allow the recording of data obtained in a file in ASCII format.

Embodiment of the invention

Figure 1 shows as an example the physical parts that make up the equipment. The support is made by square galvanized steel profiles, a plate 3 mm thick base with claw-like legs, as shown  in figure 2. Attached to this shaft and being able to choose different positions, the mechanism of spindle nut (figure 3 and 4) consisting of a tube 40 x 40 mm square profile exterior, which carries internally a screw or spindle that will have a length of 50 cm and a step helical p = 0.5 cm / turn, this runs longitudinally the outer tube and supports at the upper end in an axial bearing which closes this tube, emerging a coupling fast drive motor inside a 28 tooth gear plastic. The screw nut (spindle) is in solidarity with the inner concentric tube, such that by rotating the screw and the nut being the moving part it moves through the inner tube of larger diameter dragging to the inner tube, that moves telescopically up or down depending on the direction of rotation of the motor.

The mobile inner tube will have a load cell based on strain gauges, 2450 N which it will allow to measure the force that is exerted when the tip Conical penetrates the ground. Attached to the gear where the drive motor, is another gear of equal number of teeth (same diameter) inserted in the axis of the optical encoder, so that the turning movement is transmitted to the encoder and will allow measure the position of the conical tip while penetrating the ground.

Both rod and cone dimensions as of the test procedure they are standardized according to ASAE Standard S313.3. Soil cone penetrometer, 1999.

The electronic part is composed of electronic sensors and conditioners whose arrangement is shown in figure 5. The feeding is done by two 12V batteries put in series since the conditioner requires 24V power

The necessary software is explained in the section 2.3.

Claims (6)

1. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer", characterized in that its size, configuration and weight, makes it a portable measuring instrument by a single operator and its operation is with An electric motor that runs on batteries. 2. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer" according to claim 1, characterized by having a support structure with the configuration and arrangement reflected in the figures shown and a system of mobile guide to select different working heights and also, transport position. 3. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer" according to claims 1 and 2, characterized by having a screw-spindle mechanism as a means of transforming a rotation movement into another of translation. In the case that the screw rod is presented, it receives the rotation of the electric motor and the nut moves axially along the screw. 4. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer" according to claims 1 to 3, characterized by equipping a commercial load cell as a sensor for penetrating forces and a device for the so-called Encoder to know the position of the conical tip in the penetration process. 5. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer" according to claims 1 to 4, characterized by displaying the IC-Depth graph, simultaneously to the test, on the screen of a laptop (PC), being able to be stored, or deleted from its memory. 6. Model of "Portable Penetrometer, equipped with spindle mechanism, for agricultural uses, managed with microcontroller and computer" according to claims 1 to 5, characterized by incorporating the following elements for proper operation, as part of the hardware as well as its physical location on the device: Load cell. High resolution optical encoder. Signal conditioner for the load cell, that amplifies the output signal and also feeds the voltage recommended to this cell. Digital analog converter (A / D). RISC architecture microcontroller. Connection to the computer through the port parallel of this one. Equipment and own power batteries laptop.