GB2168409A - Hydraulic ram extension measuring device - Google Patents

Abstract

A hydraulic ram 10 comprises a cylinder 11, and a piston 12 movable with respect to the cylinder when hydraulic fluid flows to or from the ram. A fluidics oscillator 15 is connected to the ram such that when fluid is supplied to or exhausted from the ram, the fluidics oscillator 15 is caused to oscillate at a rate related to the rate of flow of hydraulic fluid. The fluidics oscillator 15 is arranged to generate a signal for use in calculating the quantity or hydraulic fluid which has flowed to or from the ram. If the dimensions of the ram are known and the quantity of hydraulic fluid supplied to or from the ram is calculated, the degree of extension of the ram can then be calculated for display, monitoring, signal generating or other purposes. <IMAGE>

Description

SPECIFICATION Hydraulic rams The invention relates to hydraulic rams, for example the hydraulic rams of hydraulic underground roof supports.

It is particularly concerned with the detecting of the degree of extension of the rams.

Hydraulic rams are widely used in underground roof supports, both to support a roof engaging canopy above a base unit, and to advance a roof support to a new position, for example as a mineral (e.g. coal) face is progressively cut away. In long wall mining for example, there may be a row of roof supports extending along the mine face. As mining advances, the supports are moved forward, sequentially, until they are all in a new position.

With most known supports, there is no way of detecting the degree of extension of the rams between the limiting positions of fully extended and fully retracted. The limiting positions can easily be detected by limit switches or striker valves but it is difficult to monitor the movement of the ram between these positions.

In many instances however, it is highly desirable to be able to monitor the degree of extension of the rams, for instance in order to monitor and control the position of one underground roof support with respect to adjacent roof supports, and a notional reference line for example to straighten up a mine face.

Methods of monitoring the degree of extension of hydraulic rams are known, but have several drawbacks. One known method involves the use of a helical rod which co-operates with the piston of a ram so that as the ram moves longitudinally with respect to its cylinder during its working stroke, the rod is rotated. The rotation of the rod operates a rotary potentiometer which hence gives an electrical indication of the degree of extension of the ram. However this known device is difficult and hence expensive to make and install, is unreliable because of wear and other mechanical problems, and is difficult to service because of its position within the ram.

Other proposed solutions, for example involving the use of a large number of monitoring switches, are also expensive and difficult to implement. They require physical modification of the rams and may require appreciable electrical power, an undesirable requirement in underground situations where power consumption must be kept low to reduce the risk of explosions.

We have now developed a means of detecting the degree of extension of a hydraulic ram which requires no modification of the ram itself, requires little or no electrical power, but is cheap, robust and reliable.

The invention provides a hydraulic ram comprising a cylinder, a piston movable with respect to the cylinder when hydraulic fluid flows to or from the ram, and a fluidics oscillator connected to the ram such that when fluid is supplied to or exhausted from the ram, the fluidics oscillator is caused to oscillate at a rate related to the rate of flow of hydraulic fluid, and the fluidics oscillator being arranged to generate a signal for use in calculating the quantity of hydraulic fluid which has flowed to or from the ram.

Clearly if the dimensions of the ram are known and the quantity of hydraulic fluid supplied to or from the ram can be calculated, the degree of extension of the ram can also be calculated for display, monitoring, signal generating or other purposes.

Since the fluidics oscillator can simply be connected in a fluid flow path to or from the ram, no modification of the ram itself is required.

The fluidics oscillator can be arranged to generate its own electrical signal, thus avoiding the need for an external power supply.

Fluidics oscillators can be cheaply manufactured having virtually no moving parts, and can hence be made robust and reliable.

Preferably the fluidics oscillator has at least one stagnation chamber in which the pressure oscillates during use, the pressure oscillations of the stagnation chamber being arranged to cause a signalling member to oscillate past an inductive pickup, thus producing an oscillating electrical signal. This signalling member is the only moving part required by the fluidics oscillator. Hence the number of oscillations is converted to a ram extension signal.

Preferably the signalling member is arranged to oscillate in an oscillation chamber, the fluidics oscillator having two stagnation chambers and the two stagnation chambers being connected respectively to the ends of the oscillation chamber.

The invention includes an underground roof support fitted with at least one ram in accordance with the invention.

By way of example, a specific embodiment of the invention will now be described, with reference to the single accompanying Figure, which is a diagrammatic illustration of an embodiment of hydraulic ram according to the invention.

The hydraulic ram 10 shown in the Figure comprises a cylinder 11 and an associated piston 12 which can be extended with respect to the cylinder by applying hydraulic fluid to a cylinder inlet 13.

When the ram extends, hydraulic fluid trapped on the upper side of the piston as viewed in the Figure exhausts through an outlet 14.

Connected between the source of hydraulic fluid (not shown) and the inlet 13 is a fluidics oscillator 15. This oscillator 15 splits the main fluid flow passage 16 into two diverging passages 16a and 16b, each defined by an associated Coanda wall 17a, 17b, and a common central deflector 18.

When fluid which is travelling along the main flow path 16 enters the fluidics oscillator 15, the fluid initially tends to stick to a single one of the Coanda walls, 17a or 17b, because of the well known Coanda effect. Thus fluid tends to travel either along the flow path 16a or the flow path 16b. On reaching the obstruction caused by an associated shoulder 19a or 19b however, there is a build-up in pressure in an associated stagnation chamber 20a or 20b. The two stagnation chambers 20a and 20b lead back to the separation zone 21 and when there is a pressure build-up in one of the stagnation chambers, it causes the jet of fluid attaching to the associated Coanda wall to flip over and attach to the other Coanda wall. There is then a build-up of pressure in the other stagnation chamber and the jet of fluid changes position once again.There is thus a continuous oscillation of the jet and a continuous fluctuation of pressure in the stagnation chambers 20a and 20b. The rate of oscillation is directly related to the rate at which fluid flows to the ram 10.

The oscillation chambers 20a and 20b are respectively connected to the ends of an oscillation chamber 22 in which there is positioned a steel ball 23. The alternating raising and lowering of the pressures in the stagnation chambers causes the steel ball 23 to oscillate back and forth in the oscillation chamber. An inductive pickup 24 is positioned adjacent to the central portion of the oscillation chamber 22 and the pickup 24 is connected to a remotely located electrical monitoring device 25. The amplitude of oscillation of the steel ball 23 can be adjusted by inserting or withdrawing to a greater or lesser extent two pins 26 which project into the ends of the oscillation chamber 22.

The monitoring device 25 receives an oscillating electrical signal from the pickup 24. The device 25 amplifies this signal and converts it into a digital count which is directly related to the quantity of hydraulic fluid fed to the ram 10.

There is a linear relationship such that if the counter of the monitoring device 25 is set to nought when the ram 10 is fully retracted and the counter shows a count of 2000 after the ram has been fully extended, then it can be assumed that when the counter shows a count of 1000, the ram is half extended, provided that the bore of the cylinder does not vary along its length, and provided that there are no leaks.

At very low flow rates the fluidics oscillator 15 may not oscillate at all, and at very high flow rates cavitation may occur, but over a wide working range the linear effect described above will be maintained.

The fluidics oscillator illustrated in the diagram needs no external power supply and can be made intrinsically safe for use underground. It has low resistance to flow and can be manufactured cheaply by CNC milling, diecasting or plastics moulding.

The fluidics flowmeter acts as an inferential position transducer. Thus the position of the piston 12 with respect to the cylinder 11 can only be inferred, rather than positively determined, but it is possible to infer the position with considerable accuracy. Of course no signal is produced when there is no fluid flow and so information concerning the position of the ram has to be stored in the monitoring device 25. Furthermore it is desirable for the counter of the monitoring device 25 to be reset at the end of each stroke of the ram to avoid cumulative errors.

When the ram, together with its fluidics oscillator has been calibrated and is in use, the total count which will be recorded by the monitoring device 25 through a full working stroke will be known. If a count significantly less than this is recorded, this will indicate that the ram has not completed its stroke but has stopped because of some other reason, for example physical obstruction, cancellation of a control signal, hydraulic failure, or some other fault condition. If a substantially greater count is recorded, it can be inferred that the ram is leaking.

The invention is not restricted to the details of the foregoing embodiment. For example, the signal provided by the pickup 24 may be put to more sophisticated purposes. For example it may be used for control purposes, rather than mere monitoring purposes. Furthermore a numerical count related to the position of the ram may be converted into a form more closely related to the position of the ram. The device 25 might for example have a display giving the extension of the piston as a percentage of the maximum possible extension, or as an actual distance from nought to the fully extended distance.

The signal from the pickup 24 may be used by appropriate control hardware and software to infer the actual speed of movement of the ram.

The arrangement may be used for monitoring and/or control purposes on a healthy ram and for diagnostic purposes in fault conditions.

In some circumstances it may be desirable to monitor the flow out of the ram when the ram retracts. The fluidics oscillator shown in the diagram will not function in the reverse direction but valve gear may be provided to feed the returning fluid through the fluidics oscillator in the right direction.

Alternatively two fluidics oscillators may be provided, with non-return valves arranged to direct flow through the appropriate device.

Claims (8)

1. A hydraulic ram comprising a cylinder, a piston movable with respect to the cylinder when hydraulic fluid flows to or from the ram, and an oscillator connected to the ram such that when fluid is supplied to or exhausted from the ram, the oscillator is caused to oscillate at a rate related to the rate of flow of hydraulic fluid, and the oscillator being arranged to generate a signal for use in calculating the quantity of hydraulic fluid which has flowed to or from the ram.

2. A hydraulic ram as claimed in claim 1, in which the oscillator is connected in a fluid flow path tb or from the ram.

3. A hydraulic ram as claimed in claim 1 or claim 2, in which the oscillator is arranged to generate its own electrical signal, thus avoiding the need for an external power supply.

4. A hydraulic ram as claimed in any one of the preceding claims, in which the oscillator has at least one stagnation chamber in which the pressure oscillates during use, the pressure oscillation of the stagnation chamber being arranged to cause a signalling member to oscillate past an inductive pickup, thus producing an oscillating electrical sig nal.

5. A hydraulic ram as claimed in claim 4, in which the signalling member is arranged to oscillate in an oscillation chamber, the oscillator having two stagnation chambers and the two stagnation chambers being connected respectively to the ends of the oscillation chamber.

6. A hydraulic ram as claimed in any one of the preceding claims, in which the dimensions of the ram, and the calculation of the quantity of hydraulic fluid which has flowed to or from the ram are used to calculate the degree of extension of the ram for display, monitoring, signal generating or other purposes.

7. A hydraulic ram constructed and arranged substantially as herein described with reference to the accompanying drawing.

8. An underground roof support fitted with at least one ram as claimed in any one of the preceding claims.