GB2194907A

GB2194907A - Machine tools and automatic loading equipment therefor

Info

Publication number: GB2194907A
Application number: GB08621786A
Authority: GB
Inventors: William Randal Vaughan
Original assignee: W R Vaughan & Associates Limit
Current assignee: W R Vaughan & Associates Limit
Priority date: 1986-09-10
Filing date: 1986-09-10
Publication date: 1988-03-23
Also published as: GB8621786D0

Abstract

Relative linear displacement of two elements (11, 12) of a machine tool or of automatic loading equipment for a machine tool along parallel sideways (13, 14) is achieved by way of a linear electric motor (16) having its stator (17) and armature (18) fixed respectively to the two elements (11, 12). Control is by computerised numerical control system with relative positional information supplied by conventional means (21-23). <IMAGE>

Description

SPECIFICATION Machine tools and automatic loading equipment therefor This invention relates to machine tools and to automatic loading equipment for machine tools.

A machine tool may have one, or two, or indeed any number of slideways between respective pairs of elements of the machine tool to permit relative linear displacement therebetween, for example between a fixed bed and a saddle, or a bed and a turret, or a saddle and another element on a cross-slide, and so forth. Modern computerised numerically controlled (CNC) machine tools routinely produce compound movements simultaneously of two or more linear slideways to produce complex movement of an element. Automatic (robotic) loading equipment for machine tools may also have such slideways.

Although hydraulic cylinders and air cylinders are sometimes used, screw-threads, plain and re-circulating, driven by rotary electric motors are most common.

Although linear electric motors are known in themselves, it has never been proposed to use a linear electric motor in a machine tool, nor in automatic loading equipment for a machine tool. We presume that this is because it has hitherto been believed that a linear electric motor is not suitable because of the very high positional accuracy required in a machine tool and in automatic loading equipment and the large, sometimes unpredictable, forces involved.

The present invention arises from a realisation that a linear electric motor may, after all, be used to produce relative linear displacement between two elements of a machine tool or its associated automatic loading equipment along a slideway. Releasable clamping means may be incorporated for clamping the two elements against relative displacement when their relative positions are required to be fixed. Alternatively or additionally, a CNC system may control the linear electric motor, for resisting relative displacement e.g. due to machining forces. The slideway may be associated with a respective measuring device for measuring actual relative displacement for the purpose of controlling the linear motor.

The machine tool or automatic loading equipment may have at least one further slideway extending in a different direction and with a corresponding linear electric motor extending in that direction.

For simplicity of construction, a stator and an armature of the or each linear motor may be mounted directly, one to one element and the other to the other element of the pair of elements which are adapted for the relative displacement along the or each slideway.

The machine tool or automatic loading equipment may well have two or more parallel slideways between a given pair of elements.

The invention will be described by way of example with reference to the accompanying drawing, the single figure of which is a section through part of a machine (the rest being broken away) embodying the invention.

The illustrated machine 10 may be a machine tool or alternatively may be automatic (robotic) loading equipment for use with a machine tool, e.g. to pick-up workpieces to be machined, place the workpieces in the machine tool for machining and afterwards remove them from the machine tool.

The illustrated machine 10 comprises a first element 11 which, if the machine is a machine tool, may be a bed, saddle, column or other structional member and a second element 12 which may be a saddle (if element 11 is a bed) or table cross-slide, spindle head, turret slide or other structural member.

Between the two elements 11 and 12 are two parallel linear slideways, namely, a veeslideway 13 and a flat slideway 14. These slideways are conventional. Other conventional slideways may be provided if desired, for example, rolling-element, oil-hydrostatic or gas-hydrostatic slideways. A conventional keeper strip 15 is fitted by means of bolts 15a to element 12 to keep it from accidental disengagement from element 11.

To produce relative movement or displacement between elements 11 and 12 there is provided a linear electric motor 16, extending parallel to the slideways 13 and 14, and having a stator 17 fixed to element 11 and an armature 18 fixed to element 12. The stator 17 comprises a pair of stator cores 19a, 19b and associated windings 20a, 20b either side of the armature 18, as with a conventional linear electric motor.

Detection of relative displacement of elements 11 and 12 is done by way of conventional means, such for example as an optical grating 21 fixed to member 12 and an electro-optical transducer 22 fixed to member 11 and having a fibre-optic output signal connection 23, shown broken away. Alternatively a linear resolver (inductosyn) may be used. The linear motor 16 is controlled (by means not shown) in accordance with the output signal from transducer 22 to produce the required relative displacement of elements 11 and 12.

Control of the linear motor 16 may advantageously be by way of a, suitably programmed, computerised numerical control system, not shown. This can provide variable force control (like variable torque control of a rotary motor).

Because the drive by linear motor 16 is not positive drive, damping of the relative motion of elements 11 and 12 requires to be considered. Sufficient damping may be expected to be provided by slideways 13 and 14 themselves, being a vee-slideway and a flat slideway respectively, but additional damping may be necessary for other forms of slideway.

Depending on the nature of elements 11 and 12 and hence the direction of relative displacement desired, the slideways 13 and 14 and motor 16 may extend horizontally or vertically or any angle in between and also any angle in azimuth.

The output at connection 23 may provide a read-out at, for example, an operators's panel or other position-display equipment, not shown.

Conventional controllable clamping means, not shown, is preferably provided to fix the relative positions of elements 11 and 12, if desired, between successive relative displacements.

Claims

1. A machine tool having at least one linear slideway between two elements so that one element is supportable by and linearly movable relative to the other element, and an electric motor arranged to move said one element relative to said other element, characterised in that the electric motor is a linear electric motor extending parallel to the direction of linear movement and having a stator and an armature fixed one to said one element and the other to said other element.

2. A machine tool as claimed in Claim 1 having a further linear slideway between said one element and a further element respectively so that said further element is supportable by and movable relative to said one element, and a further linear electric motor arranged to cause relative linear movement between said further element and said one element in the respective direction.

3. A machine tool as claimed in Claim 1 or 2 wherein the or each pair of relatively linearly movable parts, one supported directly by the other, is fitted with relative position-sensing means connected to means for controlling the associated linear electric motor.

4. A machine tool as claimed in any preceding claim and further comprising means for fixing the relative positions of elements between movements.

5. A machine tool as claimed in any preceding claim wherein the or each linear electric motor is controlled by a computerised numerical control system.

6. Automatic loading equipment for a machine tool, said equipment having at least one linear slideway between two elements so that one element is supportable by and linearly movable relative to the other elements, and an electric motor arranged to move said one ele ment relative to said other element, characterised in that the electric motor is a linear electric motor extending parallel to the direction of linear movement and having a stator and an armature fixed one to said one element and the other to said other element.

7. Automatic loading equipment as claimed in Claim 6 having a further linear slideway between said one element and a further element respectively so that said further element is supportable by and movable relative to said at least one element, and a further linear electric motor arranged to cause relative linear movement between said further element and said one element in the respective direction.

8. Automatic loading equipment as claimed in claim 6 or 7 wherein the or each pair of relatively linearly movable parts, one supported directly by the other, is fitted with relative position-sensing means connected to means for controlling the associated linear electric motor.

9. Automatic loading equipment as claimed in any one of claims 6 to 8 and further comprising means for fixing the relative positions of elements between movements.

10. Automatic loading equipment as claimed in any one of claims 6 to 9 wherein the or each linear electric motor is controlled by a computerised numerical control system.