WO2005120771A1

WO2005120771A1 - Tool integrity monitoring device

Info

Publication number: WO2005120771A1
Application number: PCT/GB2005/002287
Authority: WO
Inventors: Martin John Lenzini
Original assignee: Martin John Lenzini
Priority date: 2004-06-11
Filing date: 2005-06-10
Publication date: 2005-12-22
Also published as: GB0418194D0; GB0413057D0

Abstract

A device for sensing breakage, movement or absence of a machine component comprises a component sensor which is connected to a source of pressurised fluid and which is urged to a rest position by spring means. In the rest position it permits release of pressurised fluid. The component sensor is movable to a first displaced position in which it mocks release of pressurised fluid. When an unbroken component is suitably located it maintains the component sensor in the first displaced position so that no pressurised fluid will flow. If the component is broken or absent, pressurised fluid may be released and may trigger an alarm condition. Another aspect of the invention provides a machine assembly which includes the device. In yet another aspect of the invention, the device comprises a sensor block having an electrically conductive pathway therethrough, said pathway being interupted by two spaced apart sensor passages each of which intersects the pathway.

Description

TOOL INTEGRITY MONITORING DEVICE

BACKGROUND OF INVENTION

The present invention relates to a device for sensing breakage, movement or absence of a component for a machine, notably to a device for detecting breakage of a machine tool, and to a machine assembly incorporating the device.

SUMMARY OF INVENTION

According to an aspect of the present invention there is provided a device for sensing breakage, movement or absence of a machine component, the device comprising a component sensor which is connected to a source of pressurised fluid and which is urged to a rest position by spring means, in which rest position it permits release of pressurised fluid; the component sensor being movable to a displaced position in which it blocks release of pressurised fluid.

The sensor may be maintained in the displaced position by a component. If the component moves away, or is broken or absent, the sensor will adopt the rest position and permit release of pressurised fluid (notably pressurised air) which may in turn trigger an alarm condition or shut down a machining operation. Removal of the component or movement of the component in a first direction will release the component sensor to be driven to the rest position by the spring means. In a preferred embodiment, the device is constructed and arranged so that movement of the component in a second direction, typically an opposite direction to the first direction, will displace the component sensor to a second displaced position at which it permits release of pressurised fluid. Thus, the device will release pressurised fluid when the component is moved in different directions (corresponding to fault conditions) and also when the component is absent or broken. The device may be used in many applications, particularly those involving machining of components in a workshop or factory. The component may, for example, comprise a machine tool, or a workpiece which is being held for machining in a vice, a vacuum chuck, or on a vacuum hold- down table. Movement of the component will indicate a problem and trigger remedial action.

According to another aspect of the present invention there is provided a device for sensing breakage, movement or absence of a component projecting from a component holder, the device comprising a sensor block having a fluid passage there through for connection at one end to a source of pressurised fluid, the sensor block being provided with two spaced apart sensor passages each of which intersects the fluid passage; one sensor passage containing a component holder sensor and the other sensor passage containing a component sensor, each sensor comprising a blocking portion which will substantially block the fluid passage and an open portion which will at least partially open the fluid passage; wherein each sensor is urged by spring means to a rest position in its sensor passage in which the open portion of the component sensor is aligned with the fluid passage and in which a blocking portion of the component holder sensor is aligned with the fluid passage so that substantially no fluid can pass through the sensor block; the arrangement being such that when a component holder carrying an intact component is brought into contact with the device, with the component holder in contact with the component holder sensor and with the component in contact with the component sensor, and moved against the spring force to a test position in which the open portion of the component holder sensor is aligned with the fluid passage, the component sensor will be moved so as to align a blocking portion with the fluid passage so that substantially no fluid can pass through the sensor block; whereby if the component is broken or missing the component sensor will be disposed in its rest position when the component holder is in the test position so that fluid can pass through the sensor block.

The component may be a machine tool, and for convenience the invention will be described with reference to this preferred embodiment .

The spring means preferably comprises a coil spring, but other mechanical equivalents may be employed, for example a leaf spring, elastic or pneumatic means.

The open portion may comprise a hole, a groove, a waisted portion, or any other suitable opening that will permit fluid flow through the sensor.

The passage of fluid through the fluid passage of the sensor block may trigger an alarm condition or automatically stop the machine. This may be achieved by activation by fluid pressure from the sensor block or by means of a low pressure sensor on the fluid supply. Typically the pressurised fluid will be pressurised air, which may be provided by a machine shop compressor. Machine tools are typically provided with a low pressure sensor as a standard failsafe mechanism when used with numerical computer controlled manufacturing machines.

The released pressure from exhaust of the sensor block could be transferred to a normally closed pressure sensor switch which opens when pressure is sensed. This could be wired in series with any circuit to stop the machine, such as an emergency stop, door switch circuit or any other machine function used to stop a machine or have its own circuit dedicated to this function. An advantage of this arrangement would be that the pressure switch could easily be adjusted for sensitivity by adjusting the contact pressure inside the switch which is normally variable from 2-10 bar (200 kPa - 1 MPa)

According to a further aspect of the invention there is provided a machine assembly comprising a component holder with a component projecting therefrom, and a device for sensing breakage, movement or absence of the component, the device comprising a sensor block having a fluid passage there through connected at one end to a source of pressurised fluid, the sensor block being provided with two spaced apart sensor passages each of which intersects the fluid passage; one sensor passage containing a component holder sensor and the other sensor passage containing a component sensor, each sensor comprising a blocking portion which will substantially block the fluid passage and an open portion which will partially open the fluid passage; wherein each sensor is urged by spring means to a rest position in its sensor passage in which the open portion of the component sensor is aligned with the fluid passage and in which a blocking portion of the component holder sensor is aligned with the fluid passage so that substantially no fluid can pass through the sensor block; the arrangement being such that when a component holder carrying an intact component is brought into contact with the device, with the component holder in contact with the component holder sensor and with the component in contact with the component sensor, and moved against the spring force to a test position in which the open portion of the component holder sensor is aligned with the fluid passage, the component sensor will be moved so as to align a blocking portion with the fluid passage so that substantially no fluid can pass through the sensor block; whereby if the component is broken or missing the component sensor will be disposed in its rest position when the component holder is in the test position so that fluid can pass through the sensor block; the assembly further comprising means for triggering an alarm condition and/or stopping a machining operation when pressurised fluid passes through the fluid passage.

A tool breakage detection device according to a preferred aspect of the invention may be cost-effectively retrofitted to existing machines and may be incorporated as an option for new machines. The device will stop a machine automatically upon tool breaking and thus stop further damage being caused.

While the device is described with reference to its preferred connection to a source of pressurised fluid, it will be understood that the device could also be used with connection to a source of partial vacuum (ie, negative fluid pressure) and that such an arrangement is within the scope of the invention.

The tool breakage sensor could be mounted with a protruding stop member to act as a component positioning aid when parts are loaded to a machine vice or similar apparatus. The sensor may also have a vacuum generator mounted in its base with an integral cut-out which will operate in the event of vacuum loss. This arrangement enables the sensor to act as a multipurpose device all within relatively small confines of space and only requiring a single air supply pipe for full functionality. Each of these items could be modular and added later if and when desired. A similar movement sensor could be added to a machine vice behind a jaw of the vice to stop a machine starting if the vice is not correctly clamped.

Other aspects and benefits of the invention will appear in the following specification, drawings and claims.

DETAILED DESCRIPTION

The invention will now be further described, by way of example, with reference to the following drawings in which:

Figures 1-3 are part-sectional views through a device for sensing or detecting breakage, movement or absence of a component projecting from a component holder in accordance with an embodiment of the present invention;

Figure 4 is a part-sectional view similar to Figure 2, through a device in accordance with an alternative embodiment of the invention; and . Figure 5 illustrates a further embodiment of a device in accordance with an aspect of the present invention.

The tool breakage detector as shown in Figure 1 consists of a sensor block 5 which has a fluid passage 11 through it, connected at one end to a compressed air inlet 10. The sensor block 5 has a first tool holder sensor 8 and second tool sensor 3 inserted into holes bored into the top of the sensor block 5. The holes each intersect the fluid passage 11. Return springs 2 are disposed below the tool sensors 3, 8 and urge the tool sensors upwards as shown in Figure 1. The sensors 3, 8 in this example are pins but could be any type of pneumatic switch. Each sensor has an open portion 4, in this example a groove that allows air to flow past when it is aligned with the fluid passage 11. The first sensor, nearest the compressed air inlet, is the tool sensor 3. This sensor has a rest position in which the open portion 4 is in line with the fluid passage 11. The second sensor, further from the compressed air inlet, is the tool holder sensor 8. The tool holder sensor 8 has an open portion 4 which is not normally in line with the fluid passage 11 and shuts off the airflow when in a rest state and not in contact with the tool holder 1. Both tool sensors 3 and 8 are extensively adjustable to accommodate different tool lengths. To check more than one tool 9 the length of each tool 9 which extends from the tool holder 1 should be set to the same value. Alternatively, any number of tool sensors 3 could be mounted in line with the tool holder sensor 8, each of which may extend to a different distance from the sensor block 5 when in its rest position. The appropriate tool holder sensor 3 would be selected and used for a particular tool 9.

To the sensor block 5 is connected an air supply which is taken from between a low air pressure sensor 6 and a small restriction hole 7 which is fed via a normal machine shop compressor. The pressure sensor itself forms part of standard failsafe on virtually all computer numerical controlled manufacturing machines. The exemplified machine assembly is a machining centre but could be of any type.

Figure 2 shows a good tool 9 in non-broken condition actually in position to be checked. This would normally occur after the tool has finished being used and before it is automatically changed for the next tool although the tool could be checked any number of times throughout the machining cycle and any number of times. First the sensors 3, 8 are adjusted so both start to contact the tool 9 and tool holder 1 simultaneously. As the tool 9 is moved down using the machine vertical axis movement the air flow through the tool sensor 3 is shut off. Although the tool holder sensor 8 has its open portion 4 aligned with the fluid passage, no airflow through the sensor block 5 is allowed and the machine is allowed to carry on and complete the next task. Figure 3 shows a tool 9 in a broken condition actually in position to be checked. In this case the broken tool 9 does not press on the tool sensor 3 to shut off air flow through the tool sensor 3 and when the movement of the tool holder brings the tool holder sensor 8 inline air is allowed to escape through the tool sensor block 5.

The fluid passage 11, which allows air to escape, is considerably larger than the restriction hole 7, causing air pressure at the pressure switch 6 to drop. This will cause the machine to go into emergency stop condition and stop the machine from carrying on in its cycle. At this stage the operator is alerted to a problem ready for him to replace the tool. This stopping of the machine would stop any subsequent tools from excessive load and breaking.

Other alarm means could be actuated by passage of air through the sensor block 5. For example, a horn could be sounded or a visible sensor could be ejected from the sensor block or from an attachment thereto to alert an operator to the tool breakage .

Referring now to Figure 4, an alternative embodiment of the device is shown. Here, the component sensor 3 is provided with a second open portion 4A located closer to the tool 9 than the first open portion 4. If the tool 9 is moved sufficiently far towards the sensor block 5 (which movement may be indicative of a fault in a support such as a vacuum chuck) this movement will bring the second open portion 4A into line with the fluid passage 11 and trigger an alarm condition. Optionally, the tool holder sensor 8 may be provided with a second open portion 4A, so that movement of the entire tool holder 1 with the tool 9, in the direction of arrow 12 towards the sensor block 5 will trigger the alarm condition by alignment of both second open portions 4A with the fluid passage 11.

In the device shown in Figure 5, the sensor block 5 is provided with a laterally extending stop member 13, in this example an adjustable bar, which serves as a component positioning aid for a component which is to be machined on a work surface (not shown) . The sensor block 5 may be mounted on or adjacent to a machine vice and may provide functionality useful to operation of the vice or an associated workpiece support. In the present example, the base 5' of the sensor block 5 has mounted within it a venturi which is operatively connected to the compressed air inlet 10 and which produces a partial vacuum. The vacuum outlet may be connected to suitable machinery or equipment by means of vacuum tubing 14. The venturi may be provided with a cut-out which may be used to halt a machining operation in the event of vacuum loss.

Thus, one aspect of the invention provides a multipurpose device comprising a tool breakage sensor, an adjustable component location device and an integral vacuum generator with built-in emergency vacuum loss cut out.

It will be understood that the principles embodied in the above examples may also be employed with electrical inputs powered by mains or battery. In this case, the two tool holder sensors 3 , 8 in Figures 1-5 may be made from or coated with an electrically insulating material with portions 4 and 4A comprising electrical contacts. The sensor block 5 would also be an insulator, with electrical connections replacing the fluid passage 11. Instead of pressurised fluid, an electric signal would pass through the electrical connections 11 when a circuit is completed by movement of the sensor 3 in response to breakage or movement of a tool 9. Completion of the circuit may send a signal by wires or remotely via infra red, RF or similar means to stop the machine and/or trigger an alarm condition. When powered by battery and sensed remotely no restriction of movement of machine at all would be noted.

The main principle of this embodiment is the same with more than one sensor 3. The first sensor 3 is in contact with the tool 9, the second sensor 8 can be in contact with any moving part of a machine linked to the tool holder 1 which when in contact instructs the machine tool that the tool is being checked.

It is appreciated that certain features of the invention, which are for clarity described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for the sake of brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

While the present invention has been described with reference to specific embodiments, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.

The disclosures in United Kingdom patent application No. 0413057.1, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims

1. A device for sensing breakage, movement or absence of a machine component, the device comprising a component sensor which is connected to a source of pressurised fluid and which is urged to a rest position by spring means, in which rest position it permits release of pressurised fluid; the component sensor being movable to a first displaced position in which it blocks release of pressurised fluid.

2. A device according to claim 1, wherein the pressurised fluid is compressed air and wherein the source includes a pressure sensor provided with means for triggering an alarm condition or stopping a machining operation when pressurised air is released by the component sensor.

3. A device according to claim 1 or claim 2, further comprising a second sensor which is urged by spring means to a rest position in which it blocks release of said pressurised fluid, the second sensor being movable to a displaced position at which it permits release of pressurised fluid; whereby the pressurised fluid will be released only when the component sensor is in its rest position and when the second sensor is in its displaced position.

5. A device according to any preceding claim, wherein the component sensor is movable against the force of the spring means to a second displaced position, different from the rest position, at which it permits release of pressurised fluid.

6. A device according to claim 5, wherein the movement of the component sensor from the first displaced position to the second displaced position is in the same direction as movement from the rest position to the first displaced position.

7. A device for sensing breakage, movement or absence of a component projecting from a component holder, the device comprising a sensor block having a fluid passage therethrough for connection at one end to a source of pressurised fluid, the sensor block being provided with two spaced apart sensor passages each of which intersects the fluid passage; one sensor passage containing a component holder sensor and the other sensor passage containing a component sensor, each sensor comprising a blocking portion which will substantially block the fluid passage and a first open portion which will at least partially open the fluid passage; wherein each sensor is urged by spring means to a rest position in its sensor passage in which the first open portion of the component sensor is aligned with the fluid passage and in which a blocking portion of the component holder sensor is aligned with the fluid passage so that substantially no fluid can pass through the sensor block; the arrangement being such that when a component holder carrying an intact component is brought into contact with the device, with the component holder in contact with the component holder sensor and with the component in contact with the component sensor, and moved against the spring force to a test position in which the first open portion of the component holder sensor is aligned with the fluid passage, the component sensor will be moved so as to align a blocking portion with the fluid passage so that substantially no fluid can pass through the sensor block; whereby if the component is broken or missing the component sensor will be disposed in its rest position when the component holder is in the test position so that fluid can pass through the sensor block.

8. A machine assembly comprising a component holder with a component projecting therefrom, and a device for sensing breakage, movement or absence of the component, the device comprising a sensor block having a fluid passage there through connected at one end to a source of pressurised fluid, the sensor block being provided with two spaced apart sensor passages each of which intersects the fluid passage; one sensor passage containing a component holder sensor and the other sensor passage containing a component sensor, each sensor comprising a blocking portion which will substantially block the fluid passage and a first open portion which will partially open the fluid passage; wherein each sensor is urged by spring means to a rest position in its sensor passage in which the first open portion of the component sensor is aligned with the fluid passage and in which a blocking portion of the component holder sensor is aligned with the fluid passage so that substantially no fluid can pass through the sensor block; the arrangement being such that when a component holder carrying an intact component is brought into contact with the device, with the component holder in contact with the component holder sensor and with the component in contact with the component sensor, and moved against the spring force to a test position in which the first open portion of the component holder sensor is aligned with the fluid passage, the component sensor will be moved so as to align a blocking portion with the fluid passage so that substantially no fluid can pass through the sensor block; whereby if the component is broken or missing the component sensor will be disposed in its rest position when the component holder is in the test position so that fluid can pass through the sensor block; the assembly further comprising means for triggering an alarm condition and/or stopping a machining operation when pressurised fluid passes through the fluid passage.

9. A machine assembly according to claim 8, wherein the component comprises a machine tool or a workpiece which is being held for machining.

10. A machine assembly according to claim 8 or claim 9, wherein the pressurised fluid is compressed air and wherein the means for triggering an alarm condition and/or stopping a machining operation comprises a pressure sensor arranged to send an electrical signal to an alarm or machine control circuit when an air pressure below a predetermined value is detected.

11. A device according to claim 7 or a machine assembly according to claim 8, wherein the component sensor is provided with a second open portion and is movable against the force of the spring means to a displaced position, different from the rest position, at which the second open portion is aligned with the fluid passage.

12. A device or machine assembly according to claim 11, wherein the movement of the component sensor from the test position to the displaced position is in the same direction as movement from the rest position to the test position.

13. A device or machine assembly according to any one of claims 10-12, wherein the component holder sensor is provided with a second open portion and is movable against the force of the spring means to a displaced position, the arrangement being such that movement of the sensor together by the same distance against the spring means will bring both second open portions into line with the fluid passage.

14. A machine assembly according to claim 8, wherein the sensor block is provided with a protruding stop member suitable for acting as a component positioning aid.

15. A machine assembly according to claim 8, wherein the sensor block further comprises a venturi which is contained within external walls of the sensor block and which is operatively connectable to said source of pressurised fluid to provide a partial vacuum source.

16. A device for sensing breakage, movement or absence of a component projecting from a component holder, the device comprising a sensor block having an electrically conductive pathway therethrough, said pathway being interrupted by two spaced apart sensor passages each of which intersects the pathway; one sensor passage containing a component holder sensor and the other sensor passage containing a component sensor, each sensor comprising a blocking portion and a first conductive portion; wherein each sensor is urged by spring means to a rest position in its sensor passage in which the first conductive portion of the component sensor is aligned with the pathway and in which a blocking portion of the component holder sensor is aligned with the pathway so that no electrical signal can pass through the sensor block; the arrangement being such that when a component holder carrying an intact component is brought into contact with the device, with the component holder in contact with the component holder sensor and with the component in contact with the component sensor, and moved against the spring force to a test position in which the first conductive portion of the component holder sensor is aligned with the pathway, the component sensor will be moved so as to align a blocking portion with the pathway so that no electrical signal can pass through the sensor block via the pathway; whereby if the component is broken or missing the component sensor will be disposed in its rest position when the component holder is in the test position so that an electrical signal can pass through the sensor block via the pathway.

17. A device according to claim 16, wherein said blocking portion includes a dielectric material which makes contact with electrically conductive portions of said pathway.

18. A device according to claim 16, wherein said blocking portion is electrically conductive but does not make contact with electrically conductive portions of said pathway.