This invention is concerned with the testing or working of materials, and particularly but not exclusively the non¬ destructive testing of a material using ultrasonics.

At the present time non-destructive testing of materials by way of ultrasonics has apparatus emitting ultrasonic pulses which are directed to one side of the material and receiving the pulses on the opposite side of the material, the pulses being directed along respective jets of water at the opposed sides of the material. To maintain alignment between the water jets, the pulse emitting and receiving means are provided in a single unit, the emitter and receiver being spaced apart whereby the material to be tested can be passed therebetween. There are however limitations as to the shapes of material which can be tested by such an apparatus because of the inability of the apparatus to access complex profiles.

According to the present invention there is provided apparatus for testing or working of a material, the apparatus comprising first and second assemblies which are independently movable relative to one another, and means for synchronizing the positions and orientations of the first and second assemblies at any desired location on opposite sides of a material to be tested or worked.

For testing of a material, respective transmission paths for testing signals are maintained in alignment for transmis¬ sion of the signals relative to the material.

Preferably, the first assembly has means for emitting a jet of liquid outwardly thereof along the respective path, and means for emitting ultrasonic pulses and directing same along said path through the liquid, and the second assembly has means for emitting a jet of liquid outwardly of the assembly along the respective path, and means for receiving ultrasonic pulses along said path through the liquid.

Preferably the synchronizing means comprises a computer arrangement having a programme providing for five axes correl¬ ation between respective movable units on the first and second assemblies.

Each of the first and second assemblies may be movable with the respective movable units on the apparatus along each of three orthogonal axes, the third axis thereof extending longitudinally through the respective assembly, and each movable unit may comprise a first component mounting a second component thereon for rotation relative thereto about a fourth axis normal to the third axis, the second component mounting thereon a third component for rotation relative thereto about a fifth axis normal to the fourth axis.

Preferably also each movable unit is selectively mounted on the respective assembly by way of a kinematic mount comp¬ rising a six point location system.

An embodiment of the present invention will now be desc¬ ribed by way of example only with reference to the accompany drawings, in which:

_*

Fig. 1 is a schematic view of a machine for non¬ destructive testing of materials;

Fig. 2 is an elevation of part of the machine of Fig. 1; and

Fig. 3 is a plan of the machine part of Fig. 2.

Referring to the drawings, a machine for non-destructive testing of a material has a base 10 on which are provided a pair of long tudinally extending, parallel and spaced apart guideways 12,14, on each of which is mounted a vertically extending column 16,18 respectively. Each of the columns 16,18 is movable along the respective guideway 12,14 as hereinafter described.

Each of the columns 16,18 provides a pair of vertically extending, parallel and spaced apart guides 20,22 for movement therealong of a support structure 24 for a quill 26, the latter itself being movable in guides extending laterally

across the structure 24 and mounting, on its outwardly extend¬ ing free end, a movable unit 28. In this way the unit 28 is movable along each of three orthogonal axes.

The construction of the columns 16,18, the guideways 20,22, and the support structure 24 is described in our co-pending International Patent Applications Nlos. PCT/GB 89/00345-9 and the description thereof is incorporated herein by way of reference.

Each of the units or heads 28 has a first component 30 attached to the free end of the respective quill 26 to extend outwardly therefrom. The component 30 is selectively mounted in one of two different positions on the quill 26 using a kinematic mount comprising a six point location system. A bayonet fitting is preferably used to define the path of movement between the two positions. The component 30 has any suitable arrangement for providing a rotational drive which is imparted to a second component 32 mounted on the upper side of the component 30 for rotation relative thereto about an axis 34 extending vertically as shown in the drawings.

The component 32 has a mounting part 36 and a body part 38, the mounting part 36 being profiled whereby the body part 38 is positioned to one side of the plane through the longi¬ tudinal axis 40 of the quill 26. The body part 38 has any

suitable arrangement for providing a rotational drive output and mounts a third component 42 on a side thereof remote from the plane through the longitudinal axis 40, whereby the component 42 can rotate relative to the body part 38 about an axis 44 which is shown horizontal in the drawings.

A water jet arrangement (not shown) is mounted on the head 28 to move together with the component 42 and is thereby movable relative to the material being tested on five axes.

Associated with one of the heads 28 is an arrangement (not shown) for emitting ultrasonic pulses, these pulses being directed through the respective water jet to one side of the material under test. The other of the heads 28 has associated therewith an arrangement for receiving ultrasonic pulses through the respective water jet, after the pulses have been transmitted ^' from the emitter through the material under test. In a known manner any distortion of the pulses is respresent- ative of a flaw in the material. The pulses are transmitted and received through the water jets so as to prevent any unwanted distortion.

As shown in Fig. 1, a material to be tested can take the form, for example, of a material sheet 46 having a plurality of profiled support members 48, the sheet 46 being clamped in a frame 50 which in turn is retained at opposite ends by

respective support structures 52. The latter have wheels 54 movable in tracks 56 on the base 10 between the guideways 12,14.

Each of the heads 28 has suitable bearings providing for the required rotational drive, together with electrical sensors for providing information relevant to the position and velocity of the respective components about both rotational axes 34,44. The head 28 has the components thereof pressurised internally by way of compressed air to prevent any ingress of water from the water jet. The mounting arrangements of the ^* components of the head 28 providing the axis 44, i.e. the tilt axis, set forwardly of the axis 34, i.e. the pan axis,, provides maximum clearance for relative movement.

The two five-axes machines are completely independent mechanically although one or more of the linear axes of one of the five-axes machines may be mechanically aligned parallel to the corresponding linear axis or axes of the other five-axes machines to ensure that the machines operate in a common orthogonal frame of reference. The two five-axes machines are driven in such a manner that the axes at the outer ends of the water jets are maintained accurately co-axial, and fixed points on the respective jet axes are maintained at an accurately constant separation, at all times during any cycle consisting of acceleration, constant velocity and deceleration

elements, both linear and angular, which may be necessary to ensure the following :-

(1) a further point which lies on the jet axes and which is equidistant from the fixed points is scanned along any predetermined straight or curved line in three- dimensional space; and

(2) the jet axes are at all times maintained normal to the three-dimensional curved surface in which the above straight or curved line lies.

This may be achieved by any or all of the following means : -

1. Accurate and stiff mechanical construction of the five- axes machines by methods which are common in the co-ordinate measuring machine industry. These methods may include the use of air bearings, guideways made from granite, ceramic or steel and, for the moving parts, structural materials which have high specific stiffness such as ceramic and carbon fibre reinforced plastic.

Accurate displacement transducers for the linear and rotary axes. These may be diffraction gratings or inductive or capacitive transducers or any other type of

linear or rotary displacement transducer.

3. Accurate tachometers to give velocity signals to the servo systems.

4. Very stiff mechanical drive systems. For the linear axes, this may be achieved by using a friction drive system consisting of a drive roller in bearings on the moving element of the machine operating against a straight drive bar on the fixed structure, or vice versa The drive roller may be driven directly by. an electric motor or may be connected to the motor by a belt drive, either friction belt or toothed belt, or by friction rollers. Another method for the linear axes is the use of linear motors.

For the rotary axes, direct drive motors contained within the manipulator may be used.

5. Very stiff servo systems which include position and velocity loops for negative- feedback.

6. Very accurate servo systems having velocity feed forward elements.

Software with any or all of the following features :-

(a) Error mapping compensation for the linear and angular axes.

(b) Rotation and/or translation of one XYZ frame of reference to coincide with the other XYZ frame of reference, or of both XYZ frames of reference to coincide with the workpiece frame of reference.

(c) Compensation, both linear and angular, for gravity deflection of the water jets.

(d) Compensation, both linear and angular, for the Coriolis effect on the water jet due to rotation about the rotary axes.

(e) Compensation, both linear and angular, for the lateral lag of the water jet due to linear acceler¬ ation normal to the water jet.

(f) The ability to generate the required five-axes path for each machine from a known three-dimensional curved line lying in a known three-dimensional curved surface.

It is to be appreciated that the invention may be used for testing with other than ultrasonics. Also the inventionmay be used in the working of materials, for example in machines for cutting intricate profiles. Depending on the application, it may be that fixed points on the respective 'jet' axes need not be maintained at an accurately constant separation, and the further point which is scanned along any predetermined straight or curved line in three-dimensional space may be other than equidistant from the fixed points.

Various modifications may be made without departing from the invention. For example the construction of the moving heads may differ from that described and shown and the structure of the other parts of the machine may differ from that described and shown, provided that the moving heads are mechanically independent of one another and are able to move in synchronism.