GB2061149A

GB2061149A - A gemstone cutting machine

Info

Publication number: GB2061149A
Application number: GB8033456A
Authority: GB
Original assignee: Gersan Ets
Current assignee: Gersan Ets
Priority date: 1979-10-16
Filing date: 1980-10-16
Publication date: 1981-05-13
Also published as: GB2061149B

Abstract

A gemstone cutting machine has a sensor (28) for sensing the drag force or a force having a drag force component on a gemstone (12) in a stone carrier (13, 13') whilst it is being cut by a cutting blade (10) and means (22) responsive to the sensor for controlling the feed of the stone carrier which may be effected by, for example, a reversible feed motor (23) or actuator. <IMAGE>

Description

SPECIFICATION A gemstone cutting machine This invention relates to a gemstone cutting machine, particularly, but not exclusively, for sawing diamonds.

This invention provides a gemstone cutting machine comprising support means for a cutting blade, a stone carrier, the support means and the stone carrier being relatively movable so that in use a gemstone carried by the stone carrier can be cut through by a cutting blade supported by the support means, means for relatively moving of the stone carrier and the support means, means for sensing the drag force on the gemstone, or a force having a drag force component, or a parameter representative of said drag force or said force, and means responsive to the sensing means for controlling the moving means.

If the cutting blade is a cutting wheel, drag force is the reaction on a gemstone in a direction tangential to the wheel at the point of contact between the wheel and the gemstone.

If the cutting blade is a band blade of a band saw or a wire, drag force is the reaction on the gemstone in a direction parallel to the direction of movement of the band blade or the wire at the point of contact between the band blade or the wire and the gemstone.

Preferably, the sensing means is for sensing the drag force on the gemstone or a parameter repre sentative thereof.

Alternatively, the sensing means may be for sensing the vector sum of a component of the drag force on gemstone and a component of the cutting force on the gemstone, or a parameter representative thereof.

Preferably, the control means comprises comparator means which in use compares the drag force sensed by the drag force sensing means with a reference value.

Conveniently, the reference value is fixed.

Alternatively, the reference value is variable in accordance with one or more parameters e.g. the depth of cut, the dimensions of a stone to be cut, the rate of feed of the feed means and/or the vibration level of the cutting blade or stone.

Preferably, the machine also comprises means for reborting the blade. 'Borting' is the process of loading the cutting edge or edges of the cutting blade with an abrasive paste, commonly a diamond/ extreme pressure oil mixture.

Conveniently, the stone carrier is supported by a pivotable arm and the sensing means comprises a transducer, e.g. a displacement sensitive transducer or a force transducer, carried by or included in the arm. However, the sensing means may be a microswitch.

Conveniently, the cutting blade is a wheel rotatable by a motor clamped to a mount and the drag force sensing means comprises means for sensing the clamping moment of the torque about the motor shaft.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic perspective view of a first embodiment of a machine according to the invention, Figure 2 is a plan view of part of the embodiment of Figure 1, Figure 3 is a plan view illustrating a modification of a part of the machine shown in Figure 1, Figure 4 is a side view illustrating another modification of a part of the machine shown in Figure 1.

Figure 5 is a plan view illustrating yet another modification of a part of the machine shown in Figure 1, Figure 6 is a diagrammatic perspective view of a second embodiment of a machine according to the invention, and Figures 7-9 illustrate three different control circuits for use with the machine.

Referring to Figures 1 and 2, the machine shown therein has a phosphor bronze sawing wheel 10 loaded with an abrasive paste e.g. a diamond/oil mixture. The sawing wheel 10 is mounted in a conventional wheel holder 11 and has a belt drive (not shown) for driving the wheel.

A diamond 12 is shown held in a stone carrier which comprises two dops 13 and 13' carried respectively by two parallel elongate supports 14 and 14'. The supports 14 and 14' are each coupled to a swing arm 15 at a position remote from the associated dop 13 and 13'. The swing arm 15 is pivotable at a position remote from the supports 14 and 14' about a pin supported in spaced lugs 16 upstanding from and integral with a base 17. An adjustable position weight 18 is connected to the arm 15 in conventional manner. A screw-threaded feed spindle 19 engages a nut 20 mounted on the arm 15. The spindle 19 has a manual adjustment knob 21 at one end and bears on a platform 22 at its other end. The plafform 22 is movable in a vertical direction or in a direction having a vertical component by a reversible feed motor 23 mounted on the base 17.

The support 14' directly carries the dop 13', but the dop 13 is mounted in a holder 24 coupled to the support 14. The holder 24 has a part 25 fixed relative to the support 14, a limb 26 which mounts the dop 13, and a limb 27 which supports a displacement sensitive transducer 28. The part 25 and limb 26 are connected by two resilient fingers 29 which allow the limb 26 to be displaced relative to the part 25 in a direction parallel or substantially parallel to a tangent to the wheel 10 at the point of contact between the wheel and the diamond. The transducer 28 may be of any suitable type for measuring this displacement. Typical commercially available sensors are eddy current probes with a high sensitivity, e.g.

5-20mV/ym, linear voltage differential transformers of similar sensitivity or pneumatic proximity probes.

A visco-elastic or viscous material, may be disposed between the part 25, the limb 26 and the fingers 29 to increase damping without zero drift of the transduc er28.

The holder 24 is usually arranged so that the displacement measured thereby is related only to the drag force, i.e. the reaction on the diamond in a direction tangential to the wheel 10 at the point of contact between the wheel and the diamond, although the holder 24 could be turried about an axis normal to the longitudinal extent of the support so that the displacement measured by the transducer is related to the vector sum of a drag force component and a cutting force component, where the cutting force is the force on the diamond normal to the drag force.

A signal from the transducer 28 is used to control the movement of the platform 22 such that the forces applied to the saw blade by the gemstone are near to the maximum which the blade will withstand without buckling or damaging it with consequent damage to the diamond being cut.

In the embodiment shown in Figure 3, a holder 24' has neck portion 31 joining two co-axial limbs 32 and 33. The neck portion 31 is such that force acting on the diamond will cause the two limbs 32 and 33 to be angularly displaced relative to each other in one plane only and in order that this displacement may be measured accurately, two magnifying legs 34 and 35 are fixed rigidly to the two limbs 32 and 33 respectively. The legs 34 and 35 are normally parallel and extend in said one plane in a direction normal to the respective limb 32 and 33. The transducer 28 is supported by the free end of the leg 34 and this measures displacement of an abutment 36 on the free end of the leg 35.

By turning the holder 24' aboutthe axis of the limbs 32 and 33 the displacement measured by the transducer again can be directly related to drag force orto the vector sum of a drag force component and a cutting force component.

In the embodiment shown in Figure 4, an attachment 37 is mounted on the arm 15. The attachment 37 has a depending limb 38 which supports a microswitch 28' instead of the transducer 28. Two holders 39 and 40 depend from the attachment 37 to which they are pivotally connected at their upper ends. The holders 39 and 40 support the two dops and are biassed by a leaf spring 41 to an initial position such that a force above a certain value and being the vector sum of a drag force component and a cutting force component will displace the holders 39 and 40 angularly against the bias of the spring 41 and this displacement will operate the microswitch 28'. The bias of the spring 41 can be adjusted by a set knob 49.

In the embodiment shown in Figure 5 the dop 13 is mounted in a holder 24" coupled to the support 14.

The transducer 28 is replaced by one or more force transducers 42, such as piezo-electric transducers or strain gauge transducers, mounted on the holder 24" and protected by a sheath 43. The transducer(s) 42 measure the force applied to the diamond by the saw blade and is/are arranged so as to measure drag force, or the vector sum of a drag force component and a cutting force component.

Referring to the embodiment shown in Figure 6, the same reference numerals are used to denote similar parts. The sawing wheel 10 is mounted on an accurate spindle 9 of a drive motor 50 for the wheel 10. The motor casing is itself mounted so as to be rotatable and is restrained from doing so by an arm 8 clamped to the base. A drag force sensing device 51, such as one of the transducers previously described, senses the clamping moment of the torque about the spindle 9 and a signal representative of drag force is generated by the device 51. The displacement or force measured by the device 51 is dependent on the ratio of the distance between the axis of the spindle 9 and the device 51 and the blade radius. The device 51 could be a microswitch.

The control circuit shown in Figure 7 controls the motor 23 and hence movement of the platform 22.

The transducer 28 is connected via an amplifier 60 to a comparator 61 which compares the output of the amplifier with a reference signal which may be fixed or varied in accordance with one or more parameters e.g. the depth of cut, the rate of feed of the motor 23, the vibration level of the sawing blade or wheel 10, or stone 12, and/or the cutting force on the diamond. The output of the comparator 61 is connected to the motor 23 via a reversing switch 62 and the speed of the motor is controlled in accordance with the output of the comparator 61. As the transducer output increases the output of the comparator 61 decreases. The output of-the amplifier 60 is also connected to an input of a further comparator 63, the output of which is connected via a nor gate 70 to a coil 64 provided for operating the reversing switch 62.The comparator 63 compares the output of the amplifier 61 with a reference voltage representative of the maximum acceptable drag force and energises the coil 64 to reverse the motor 23 and retract the gemstone if the maximum acceptable drag force is reached. The coil 64is also energised by a signal fed to the nor gate 70 by a sensor 65 when the contact between the spindle 19 and platform 22 is broken or the force therebetween falls below a predetermined value indicative of a condition in which the cutting force attains a certain value limited by the weight 18. Again the motor is reversed to retract the gemstone.

The control circuit shown in Figure 8 is particularly applicable to the embodiment of Figure 4, in which the transducer 28 is replaced by a microswitch 28'.

The motor 23 rotates when the microswitch 28' is closed and contact is made between the spindle 19 and platform 22. When the force on the gemstone overcomes a preset load applied by the spring 41, the microswitch opens to de-energise the motor 23 until such time as the force falls sufficiently for the microswitch to close. Similarly, the motor is deenergised when contact between the spindle 19 and platform is broken. A timer 66 operates the reversing switch 62 to retract the gemstone if and when the motor has been de-energised for a set period.

The reversible motor 23 may be replaced by an electro-mechanical actuator or a pneumatic actuator mounted underthespindle 19.

Figure 9 shows a control circuit for a pneumatic actuator. The control circuit includes a displacement transducer 28 which senses displacement and in response thereto controls the pneumatic pressure applied to a pneumatic actuator 23'. When the drag force increases, the pressure applied to the actuator 23' also increases. Thus, the upward force on the spindle 19 increases and, consequently, the cutting force decreases. A pressure sensor 67 operates to de-energise a coil 68 when the output pressure of the transducer 28 reaches a predetermined level representative of a maximum acceptable drag force. The coil 68 is also de-energised when the contact between the platform 22 and spindle 19 is broken.

The coil 68 controls a two position magnetic actuated pneumatic switch 71 which when the coil 68 is de-energised connects the actuator 23' directly to the high pressure pneumatic line and the actuator 23' retracts the gemstone.

Instead of retracting the gemstone under the hereinbefore described conditions, the machine may be switched off.

The machine may be provided with means whereby the sawing wheel can be reborted automatically when the gemstone is retracted.

The sawing wheel 10 need not necessarily be of phosphor bronze but may be formed from an iron based alloy or a copper based alloy or a heat resistant material provided that the alloy or material is insensitive to fatigue.

Instead of the sawing wheel, a band saw may be used in conjunction with a suitable gemstone feeding system and sensing device.

The machine may include a further sensing device such as one or more additional strain gauges in the embodiment shown in Figure 5, for independently sensing the cutting force on the diamond i.e. the force normal to the drag force. In this case movement of the stone carrier towards and away from the sawing wheel may be controlled in accordance with both sensed cutting force and sensed drag force.

The reversible motor 23 may be mounted on the arm 15 for direct engagement with the screw 19 instead of placing it under the screw. In such a case the motor 23 will be provided with a friction coupling.

Claims

1. A gemstone cutting machine comprising support means for a cutting blade, a stone carrier, the support means and the stone carrier being relatively movable so that in use a gemstone carried by the stone carrier can be cut through a cutting blade supported by the support means, means for relatively moving the stone carrier and the support means, means for sensing the drag force on the gemstone, or a force having a drag force component, or a parameter representative of said drag force or said force, and means responsive to the sensing means for controlling the moving means.

2. A machine as claimed in claim 1, wherein the sensing means is for sensing the drag force on the gemstone or a parameter representative thereof.

3. A machine as claimed in claim 1, wherein the sensing means is for sensing the vector sum of a component of the drag force on gemstone and a component of the cutting force on the gemstone, or a parameter representative thereof.

4. A machine as claimed in claim 2, further comprising means for sensing the cutting force on the gemstone, the control means for the moving means being responsive to both the drag force sensing means and the cutting force sensing means.

5. A machine as claimed in any one of claims 1-4, wherein the control means comprises comparator means which in use compares the output signal of the sensing means with a reference value.

6. A machine as claimed in claim 5, wherein the reference value is fixed.

7. A machine as claimed in 5, wherein the reference value is variable in accordance with one or more parameters.

8. A machine as claimed in claim 7, wherein the reference value is variable in accordance with the depth of cut.

9. A machine as claimed in claim 7 or 8, wherein the reference value is variable in accordance with the dimensions of a stone to be cut.

10. A machine as claimed in any one of claims 7-9, wherein the reference value is variable in accordance with the rate of feed of the feed means.

11. A machine as claimed in any of claims 7-10, wherein the reference value is variable in accordance with the vibration level of the cutting blade.

12. A machine as claimed in any one of claims 7-11, wherein the reference value is variable in accordance with the vibration level of the gemstone.

13. A machine as claimed in any one of the preceding claims further comprising means for reborting the blade.

14. A machine as claimed in any one of the preceding claims, wherein the stone carrier is supported by a pivotable arm and the sensing means is carried by or included in the arm.

15. A machine as claimed in claim 2, or any one of claims 4-13 when dependent on claim 2, wherein the cutting blade is a wheel rotatable by a motor clamped to a mount and the sensing means is for sensing the clamping moment of the torque about the motor shaft.

16. A machine as claimed in claim 14 or claim 15, wherein the sensing means is a displacement sensitive transducer.

17. A machine as claimed in claim 14 or claim 15, wherein the sensing means is a force transducer.

18. A machine as claimed in claim 14 or claim 15, wherein the sensing means is a micro-switch.

19. A machine as claimed in any one of the preceding claims, wherein the moving means is a reversible feed motor.

20. A machine as claimed in any one of claims 1-18, wherein the moving means is an electromagnetic actuator.

21. A machine as claimed in any one of claims 1-18, wherein the moving means is a fluid pressure operated actuator.

22. A machine as claimed in any one of the preceding claims, wherein the control means is operable to relatively move the stone carrier and support means apart andior switch off the machine in response to the drag force reaching a predetermined value.

23. A machine as claimed in any one of the preceding claims, wherein means are provided to relatively move the stone carrier and support means apart and/or switch off the machine in response to the cutting force reaching a predetermined value.

24. A gemstone cutting machine, substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying draw ings.-

25. Cutting a gemstone using the machine of any one of the preceding claims.