AU736985B2 - Auger unit for torque transducer - Google Patents

Description

P/00/0O11 Regulation 3.2

AUSTRALIA

Patents Act 1990 0*

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "AUGER UNIT TORQUE TRANSDUCER" The following statement is a full description of this invention, including the best method of performing it known to us: "AUGER UNIT TORQUE TRANSDUCER" FIELD OF THE INVENTION This invention relates to an apparatus for accurately measuring the output torque of an auger or post hole borer. The apparatus is particularly useful for measuring torque applied to screw-in foundations.

BACKGROUND TO THE INVENTION Research relating to building foundations has led in recent years to the development of screw-in foundations. A screw-in foundation is a steel S.*1 0 product that has been designed to replace concrete foundations in many applications. The screw-in foundations are used by screwing them into the ground until a specified installation torque is achieved. The torque at which the foundation is installed determines its load capacity. If it is under-torqued it may not carry the rated load. Excess torque can lead to damage and premature failure. Applying a greater than required torque will also lead to the use of a greater number of foundations than would otherwise be required.

It will be appreciated that accurate measurement of the applied torque is required however existing methods are very inaccurate. Typically, the screw-in foundations are installed using an hydraulically powered auger drive unit. To estimate the applied torque a pressure gauge is placed in the hydraulic circuit of the auger drive unit. From a reading of the pressure gauge an estimate of the applied torque can be determined by checking a look-up table. The look-up table is compiled empirically for a specific combination of hydraulic motor and planetary gearbox.

A typical process for generating a look-up table requires performance data from the hydraulic motor manufacturer. An initial measurement of the hydraulic pressure at zero load is made, this gives an estimate of the back pressure. As the inlet pressure increases the back pressure decreases so an estimate of differential pressure must be made for each operating point. The manufacturers motor torque chart is then used to determine estimated motor output torque from the estimated differential pressure. The estimated motor io output torque is multiplied by the gearbox ratio and an estimated gearbox efficiency factor to obtain an estimated applied torque versus pressure gauge reading chart.

A typical chart is reproduced below by way of example.

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15 Pressure at Gauge (Kpa) Output Torque (Nm) 3000 0 4000 280 5000 680 6000 1120 7000 1680 8000 2730 9000 3230 10000 3970 11000 4640 12000 5150 13000 5670 14000 6400 15000 7200 16000 7740 17000 8660 18000 9500 19000 10050 20000 10600 4 Unfortunately, the output torque produced by an hydraulic motor at a given inlet pressure is governed by a large number of difficult to measure variables including operating speed; pressure drop across the motor; wear in the motor; back pressure in the hydraulic system; fluid temperature; etc.

Hence even the most carefully prepared empirical table is intrinsically inaccurate.

As a result of the unavoidable inaccuracies an operator must either over torque the foundation or risk installing the foundation at less than the specified torque. Applying more torque than is required adds to the time of 10 completing the task and therefore the cost.

OBJECT OF THE INVENTION It is an object of the present invention to provide an apparatus for directly measuring torque applied by an auger drive unit.

It is a further object of the invention to provide a torque measuring apparatus that is independent of the means of applying the torque.

Further objects will be evident from the following description.

DISCLOSURE OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in an apparatus for measuring torque applied by a rotational drive unit comprising a yoke joining a motor of the rotational drive unit to a stationary support means; a first pair of strain gauges mounted on the yoke; controller means in signal communication with the strain gauges, said controller means providing input voltage to the strain gauges and reading output voltage from the strain gauges; and signal processing means for calculating applied torque from a difference between the input and output voltages.

In one embodiment, the first pair of strain gauges are connected to a ooo* pair of balancing resistors to form a Half Wheatstone Bridge.

o 10 In a further embodiment, the first pair of stain gauges are connected to a second set of strain gauges to form a Full Wheatstone Bridge.

•In preference each pair of strain gauges forms an rosette strain gauge.

e• A display means may be provided for displaying the calculated applied 15 torque.

The stationary support means is suitably a vehicle and the display means is suitably mounted in a cabin of the vehicle for ease of view by an operator.

In preference the signal processing means may be incorporated in the controller means. The display means may also be incorporated in the controller means.

The rotational drive unit may suitably be a hydraulically driven auger drive unit.

6 The rotational drive unit may automatically stop applying torque when a predetermined torque is achieved. A switch, connected to the control means and the rotational drive unit, may be used for this purpose.

A printer may be connected to the signal processing means to produce a physical copy of the torque applied through the rotational drive unit.

BRIEF DETAILS OF THE DRAWINGS To assist in understanding the invention preferred embodiments will oleo now be described with reference to the following figures in which o10 FIG 1 shows an auger unit employed in drilling a hole; 9*FIG 2 shows a close-up view of the yoke assembly of FIG 1; FIG 3 shows a front view of the yoke with strain gauge according to a first embodiment of the invention; *ele.* FIG 4 shows a back view of the yoke with strain gauge according to 15 the first embodiment of the invention; FIG 5 shows the strain gauge configuration according to the first embodiment of the invention; and FIG 6 shows an equivalent circuit for the strain gauge according to the first embodiment of the invention.

FIG 7 shows a front view of the yoke with strain gauge according to a second embodiment of the invention.

FIG 8 shows the strain gauge and balancing resistor configuration according to the second embodiment of the invention.

FIG 9 shows an equivalent circuit for the strain gauge according to the second embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals refer to like parts.

Referring to FIG 1 there is shown an auger 1, driven by an hydraulic drive unit 2. The hydraulic drive unit 2 consists of an hydraulic motor and, usually, a planetary gearbox housed in the drive unit. As can be seen most •l clearly in FIG 2, the drive unit 2 is suspended from a yoke 3 which is in turn 10 suspended from the boom 4 of a suitable vehicle 5. The vehicle 5 supplies .hydraulic fluid through lines 6 to drive the hydraulic motor in the drive unit 2.

The vehicle 5 positions the auger 1 in the desired location and the operator controls the flow of hydraulic fluid to drive the hydraulic motor and thereby rotate the auger 1. The top yoke pin 7 is orthogonal to the lower :15 yoke pin 8 so that the auger 1 will naturally swing to a vertical position.

The arrangement depicted in FIG 1 and FIG 2 is employed for such tasks as post hole digging, foundation digging and, more recently, placing screw-in foundations. A typical screw-in foundation has a rated torque of 5000Nm. In order to estimate the correct torque a pressure gauge (not shown) may be located in the hydraulic circuit with a readout available in the operators cab 9. The operator will drive the auger until a predetermined pressure is achieved on the pressure gauge. This prior art technique is very inaccurate.

8 It will be appreciated that the yoke, which is positioned immediately above the hydraulic motor, will experience a reaction torque equal and opposite to the reaction torque applied to the hydraulically driven auger drive unit by the hydraulic motor. In the embodiments described, the yoke 3 is made from 100mm x 100mm x 9mm RHS (rectangular hollow steel) and is rated to a torque of 15000Nm.

According to a first embodiment, as shown in FIG's 3-5, a transducer is incorporated on the yoke 3. The torque on the yoke 3 is measured using .t o'e two X rosette strain gauges of the style connected in a Full Wheatstone 10 Bridge configuration.

A first strain gauge rosette 10 is applied to a front face 11 of the yoke 3 and a second strain gauge rosette 12 is applied to the rear face 13. Solder tabs 14 are provided for connection of wires to the strain gauges 10, 12. A cable 15 carries wires to and from a controller 16. There are two wires 17a, 17b carrying power to the strain gauges and two wires 18a, 18b carrying a signal from the strain gauges. The configuration is shown clearly in FIG and schematically in FIG 6.

The strain gauges 10, 12 measure the direct strain in the yoke on planes at 450 to the axis of the load. The readout is therefore a direct measure of the shear stress in the yoke along the loading axis. The yoke freely pivots at each end and is therefore incapable of transmitting any bending moment, therefore the shear stress measured is entirely due to the torsional load. The direct tensile and compressive loads on the yoke cause no direct strain at 450 to the axis of loading and therefore have no effect on the torque measurement.

Looking now at FIG 6 there is shown an equivalent circuit for the diagram in FIG 5. The variable resistors 10Oa and 10Ob form the strain gauge rosette 10 and the variable resistors 12a and 12b form the strain gauge rosette 12. A voltage is applied on lines 17a and 17b from the controller 16.

Output voltages are returned to the controller 16 on lines 18a and 18b.

The inventor has found that a suitable controller is a Ranger 5000 o* controller available from Ranger Instruments. The controller includes an 10 analogue to digital converter to convert the read voltages to digital signals for further processing. The controller also includes a signal processor that, after appropriate calibration, converts the difference between the input and output voltages to a reading of applied torque. A readout 19 is provided in the operators cabin 9 for ease of use.

15 According to a second embodiment, as shown in FIG's 7-8, a transducer is incorporated on the yoke 3. The transducer includes a strain gauge rosette 20 which is applied to the face 11 of the yoke 3. Solder tabs 21 are provided for connection of wires to the strain gauge 20. A pair of balancing resistors 22a and 22b are located remotely of the yoke 3 and are electrically connected to the strain gauge rosette 20 via a 9-pin plug 23. The 9-pin plug 23 is electrically connected to a controller 24. There are two wires and 25b carrying power to the strain gauge rosette 20 and one wire 26 carrying a signal from the strain gauge. Similarly there are two wires 27a and 27b carrying power to the resistors 22a and 22b and one wire 28 carrying a signal from the strain gauge 20. The configuration is shown clearly in FIG 8 and schematically in FIG 9.

The strain gauge 20 measures the direct strain in the yoke the same as the strain gauges 10, 12 of the first embodiment.

Looking at FIG 9 there is shown an equivalent circuit for the diagram shown in FIG 8. The variable resistors 20a and 20b form the strain gauge 20. A voltage is applied on lines 25a/27a and 25b/27b. Output voltages are returned to the controller 24 on lines 26 and 29.

10 Again, the controller 24 used is the Ranger 5000. A readout 30 of the applied torque is again provided within operators cabin 9 for ease of use. A 5O5 printer 31 is attached to the controller 24 to provide a physical copy of the torque applied to the auger 1.

A solenoid valve 32 is also connected to the controller 24 and to the 15 hydraulic motor so that when a predetermined torque is applied to the auger 1 the hydraulic motor is switched off.

It will be appreciated that the described invention provides an apparatus able to directly measure the applied torque of an auger unit.

Furthermore, the invention is completely independent of the auger, hydraulic motor or vehicle. Augers can be swapped without any requirement for recalibration or adjustment. The invention can be easily retro-fitted to existing auger drive units. Because the operator is able to achieve the required torque quickly and easily there is a considerable saving in time and therefore 11 cost.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. For convenience the apparatus has been described with reference to an hydraulic motor however the invention may also be applied to other motors, such as electric or pneumatic.

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Claims (14)

1. An apparatus for measuring torque applied by a rotational drive unit comprising: a yoke solely joining a motor of the rotational drive unit to a stationary support means; a first pair of strain gauges mounted on the yoke; controller means in signal communication with the strain gauges, said controller means providing input voltage to the strain gauges and reading output voltage from the strain gauges; and signal processing means for calculating applied torque from a V" difference between the input and output voltages.

2. The apparatus of claim 1 wherein the first pair of strain gauges are o connected to a pair of balancing resistors to form a Half Wheatstone Bridge. 15

3. The apparatus of claim 1 wherein the first pair of strain gauges are connected to a second set of strain gauges to form a Full Wheatstone e.o Bridge.

4. The apparatus of any one of the preceding claims wherein a pair of strain gauges forms an rosette strain gauge.

5. The apparatus of any one of the preceding claims wherein a signal is sent from the controller means when a predetermined torque is achieved to stop the rotational drive unit applying torque.

6. The apparatus of claim 5 wherein the rotational drive unit is switched off when a predetermined torque is achieved by a switch connected to the 13 control means and to the rotational drive unit.

7. The apparatus of any one of the preceding claims including display means for displaying the calculated applied torque.

8. The apparatus of any one of the preceding claims wherein the stationary support means is a vehicle.

9. The apparatus of any one of the preceding claims wherein the display means is suitably mounted in a cabin of the vehicle for ease of view by an operator.

10. The apparatus of any one of the preceding claims wherein the signal 10 processing means is incorporated in the controller means. S.o.

11. The apparatus of any one of the preceding claims wherein the display means is incorporated in the controller means.

12. The apparatus of any one of the preceding claims wherein the rotational drive unit is a hydraulically driven auger drive unit. S: 15

13. The apparatus of any one of the preceding claims wherein a printer may be connected to the signal processing means to produce a physical copy of the torque applied through the rotational drive unit.

14. An apparatus as substantially hereinbefore described with reference to the accompanying drawings. DATED this ninth day of May 2001. HYDRAPOWER PTY LTD By its Patent Attorneys FISHER ADAMS KELLY