GB2229119A - Gauge - Google Patents

Abstract

A gauge (10) for determining when an object, e.g. a cutting tool, is a predetermined distance (D) from a surface, e.g. a machine tool surface, has a body (11,) having a datum base surface (41) for placing against said surface and a probe (16,) mounted in the body for axial movement and which has a contact surface (18,) for contact with the tool. An electrical circuit (C1 C2,) arranged within the body includes an indicator (33,) and a battery (26,) which are connected so that the indicator is operably connected internally of the body with the battery by the probe (16) when the contact surface (18,) is a known distance (D) from the datum surface (41). The gauge is a self contained unit which does not use the machine tool as part of its electrical circuit. <IMAGE>

Description

GAUGE DEVICE This invention relates to gauges for determining when an object is a predetermined distance from a surface, and more particularly it relates to tool pre-setting devices for setting cutting tools on machine tools such as mills, lathes, turning centres, rotary and line tranfer machines, and other applications.

There are prior art machine tool setting gauges in which a probe having a contact surface is resiliently mounted in a base, the gauge further including a battery and a light emitting diode (LED) lamp such that one pole of the battery earths through the base and the machine tool, and the other pole of the battery is connected to the probe so that contact of the cutting tool against the probe completes the electrical circuit through the cutting tool and the machine tool and the L.E.D. lamp is switched on.

Other similar devices operate with electrically inducted current flowing around the machine tool and through the cutting tool.

However, all these devices suffer from the disadvantage that they do not operate with non-conductive cutting tools. Further in the event of an electrical resistance in the machine, caused by for example, non-conductive slideway surfaces, dirt, or oil film, etc., where high resistance is encountered the voltage supply to the setting gauge has to be greatly increased to cause the L.E.D. lamp to illuminate.

Similarly the lamp will not operate if the cutting tool is held in a holder which rotates within nylon bearings, or other elecrically non-conductive materials , or the spindle is insulated from the rest of the machine.

Yet another disadvantage of the prior art systems is that they can be activated by very small droplets of cutting fluid or water, such as might be caused by condensation, on the tips of a tool so that the conductive liquid completes the electrical circuit rather than direct tool contact.

The invention provides a gauge which overcomes the above difficulties.

Accordingly there is provided a gauge for determining when an object is a predetermined distance from a surface, and which comprises a body having a datum base surface for placing against said surface; a probe mounted in the body for axial movement relative thereto, and which has a contact surface for contact with said object; an electrical circuit arranged within the body and including an indicator means and a voltage source which are connected so that the indicator means is operably connected internally of the body with the voltage source, by the probe when the contact surface of the probe is a known distance from the datum surface.

Preferably the voltage source is a battery having one pole connected to the indicator means and its other pole connected to an earth formed by a base portion of the body.

Conveniently , a portion of the probe is electrically conductive and serves to operably connect the indicator means and the voltage source when the contact surface is at said known distance.

The invention will be described by way of example and with reference to the accompanying drawing which is a longitudinal cross-section through a gauge according to this invention with a schematic of the electrical circuit shown on the drawing.

Now with reference to the drawing, there is illustrated a gauge device 10 for determining when an object is a predetermined distance from a surface. This would normally be to pre-set a cutting tool tip a known distance from a work piece surface or other datums, so that its co-ordinates can be fed into a numerical control system or other like data registers.

The gauge has a cylindrical body 11 comprising a base 12 and a cap 13. The base 12 is made from an electrically conductive material and has a coaxial bore 14 therein.

The cap 13 is made of an electrically insulating material, for example, nylon, bakelite or other suitable materials and also has a coaxial stepped bore 15 therein having a smaller diameter portion 15A uppermost and larger diameter portion 15B which opens into the bore 14 in the abutting base 12. The bore 14 in the base has a larger diameter than the larger diameter portion 15B of the bore 15 in the cap.

A probe 16, in the form of a stepped piston is mounted in the cap 13 of the body 11, and is axially slideable in the stepped bore 15. The piston 16 comprises a larger diameter head portion 19, and a smaller diameter coaxial stem portion 17 which is electrically insulated from the head portion 19 by an insulator sleeve 39. The stem portion 17 slides in the smaller diameter portion 15A of the stepped bore and has an upper end contact surface 18 for contact with a cutting tool tip, and the head portion 19 is slideable in the large diameter portion 15B of the stepped bore 15. Upward movement of the piston 16 is limited by abutment of the head portion 19 against the shoulder 20 between the two different diameter portions 15A, 15B of the stepped bore 15. The axially inner portion of the probe 16, ie. the head 19, is electrically conductive.

The bore 14 in the base 12 has its bottom end closed by a power source holder 22 which comprises a cylindrical head portion 23 which closes the bore 14 and an axially inwardly projecting smaller diameter coaxial spigot 24.

An inwardly extending coaxial blind bore 25 is formed in the holder 22 and extends into the spigot 24. This serves to house a voltage or EMF source 26 e.g. a battery, and has its axially outer end closed by a screw cap 27. The holder 22 and cap 27 are both made of an electrically conductive material.

Located in the bore 14, between the holder 22 and the cap 13 is a cylindrical contact member 28 which is in the form of an inverted cup and which is made from an electrically conductive material. The contact member 28 is slideable in the bore 14 and is mounted over the spigot 24 which extends into the cup shaped contact member 28. A resilient means, in the form of a compression spring 29 is fitted over the spigot 24 and serves to bias the contact member 28 upwardly. The upward movement of the contact member 28 is limited by abutment with the cap 13. A wear plate 31 may be inserted into the cap to prevent the contact member 28 from gradually wearing away the insulated cap 13 and causing inaccuracies in the gauge.

A second resilent means, spring 32, of a lower stiffness value than the spring 29 , acts between the contact member 28 and the probe 16 to bias the probe axially upwardly until the head 19 of the probe abuts the shoulder 20. The spring 32 is of an electrically conductive material.

On the upper external surface of the cap 13, there is located an indicator means 33 which is preferably a light emitting diode (L.E.D.) lamp, but could be other suitable means such as a sound emmitter, a radio signal transmitter, or other indicative signal generators. The L.E.D. lamp 33 is connected by a first electrical circuit C1 to a contact 34 which is directly in contact with one pole of the battery 26. The contact 34 is insulated from the power source holder 22 by an insulator ring 35. The L.E.D. 33 is also connected by a second electrical circuit C2 to a second contact 36 which is housed coaxially in the upper surface of the contact member 28. The contact 36 is isolated from the contact member 28 by a second insulator ring 37 but is electrically connected to the probe 16 by the spring 32.

The probe 16 may have a hardened insert 38 in its outer contact surface 18 to prevent wear and damage to the surface. The contact surface 18 is electrically insulated from the head portion 19 of the probe 16 by the sleeve 39 to prevent reverse electrical contact through the machine and cutting tool.

The base 12 has a bottom datum surface 41, which may have magnetic inserts 40 therein for holding the gauge to a working ferrous metal surface such as a machine bed or other working datum surface.

The battery 26 has one pole earthed to the body of the gauge via the screw cap 27, holder 22, base 12, and contact member 28 which are all electrically conductive and all at the same electrical potential. The other pole of the battery 26 is connected through the electrical circuit C1, L.E.D. lamp 33, electrical circuit C2, and spring 32, to the head 19 of the probe 16 . The head 16 which is at the electrical potential of said other pole of the battery, is isolated from the earth by the non-conductive cap 13 and sleeve 39.

When the tip of a cutting tool is brought into contact with the contact surface 18 of the probe 16 and causes the probe to move axially inwardly, the L.E.D. lamp 33 will light up when the head portion 19 of the probe contacts the uppermost surface of the contact member 28 and completes the electrical circuit. The linear dimension D at which point the lamp 33 illuminates is predetermined and its co-ordinates can entered into the controls of a numerically controlled machine tool, or into the offset registers within other programmable devices, to preset the cutting tool.

If the machine tool tip overtravels, the contact member 28 can move axially downwardly against the bias of the spring 29 to absorb the overtravel and thereby prevent damage to the cutting tool,machine, or the guage.

When the gauge is mounted onto a machine,or datum surface, the base 12 will make electrical contact with the machine working surface assuming that it is say steel and of course it will be at the same potential as the base 12 . therefore, in certain circumstances , a reverse electrical circuit may be set up through the machine to the tool tip. The insulator sleeve 39 acts to prevent the L.E.D. lamp 33 from lighting on contact of the cutting tool with the probe contact surface 18.

The gauge is a self contained unit which does not rely on external electrical circuits set up through machine tools , or an external power source.

Claims (13)

1. A guage for determining when an object is a predetermined distance from a surface, and which comprises a body having a datum base surface for placing against said surface, a probe mounted in the body for movement relative thereto, and which has a contact surface for contact with said object, an electrical circuit arranged within the body and including an indicator means and a voltage source which are connected so that the indicator means is operably connected internally of the body with the voltage source by the probe, when the contact surface of the probe is a known distance from the datum surface.

2. A gauge as claimed in Claim 1 wherein the voltage source is a battery having one pole connected to the indicator means and its other pole connected to an earth formed by the body.

3. A gauge as claimed in Claim 1 or Claim 2, wherein a portion of the probe is electrically conductive and serves to operably connect the indicator means and the voltage source when the contact surface is at said known distance.

4. A gauge as claimed in Claim 2, or Claim 3 when dependent upon Claim 2, wherein the probe is slideably mounted in the body and is insulated from said earth and an inner portion of the probe is connected to said one pole via the indicator device, and said inner portion of the probe also connects to earth when the contact surface is at said known position.

5. A gauge as claimed in Claim 4 wherein said contact surface is insulated from the inner portion of the probe to prevent the indicator device and voltage source being externally connected between the probe and base surface.

6. A gauge as claimed in any one of Claims 1 to 6 wherein said body comprises a base having a bore therein, an insulating coaxial cap at the upper end of the base in which the probe is axially slideably mounted, the probe being electrically conductive and being connected to one pole of the voltage source, and a contact member located in the bore of the base and which is also electrically conductive and which is connected to the other pole of the voltage source, said indicator means becoming operative when the probe contacts the contact member.

7. A gauge as claimed in Claim 6 wherein the base is electrically conductive and forms an earth for the voltage source, the contact member is electrically connected to the base, and is resiliently biased towards the cap to be held in spaced relationship from the probe, and electrically insulated therefrom, the contact member being moveable against the resilient bias in event of further axial movement of the probe after contact of the probe against said contact member.

8. A gauge as claimed in Claim 7 wherein the voltage source is held in a voltage source holder located in the lower end portion of the bore in the base, and a spring acts between the contact member and the holder to resiliently bias the contact member against the cap.

9. A gauge as claimed in Claim 8, wherein the voltage source holder is electrically conductive and is in contact with the base such that the base, holder and contact nember are all connected to form an earth for one pole of the voltage source, said other pole of the voltage source being insulated from earth and being connected to the probe via the indicator means, the probe being resiliently biased away from said contact member by a spring which is also electrically conductive and which connects the probe with said other pole of the voltage source.

10. A gauge as claimed in any one of Claims 1 to 9 wherein the indicator means is a light emitting, audible or radio frequency transmitting device.

11. A gauge as claimed in any one of Claims 1 to 10 wherein magnets are inserted into the datum base surface of the body to hold the gauge against a machine work surface of ferrous metal.

12. A gauge as claimed in Claim 6 or Claim 7 wherein the cap is made from a polymeric material, and has a hardened metal wear plate set therein to prevent wear from contact with the contact member.

13. A gauge for pre-setting a machine tool and which is substantially as described herein and with reference to the accompanying drawings.