GB2382540A

GB2382540A - Tool manipulating device

Info

Publication number: GB2382540A
Application number: GB0128833A
Authority: GB
Inventors: John Winslow
Original assignee: Richmond Electr & Eng Int Ltd; Disarmco Ltd
Current assignee: Richmond Electr & Eng Int Ltd; Disarmco Ltd
Priority date: 2001-12-03
Filing date: 2001-12-03
Publication date: 2003-06-04
Also published as: GB0128833D0

Abstract

A device for manipulating a tool relative to a workpiece comprises a support frame 12, a column 18 movable relative to the support frame in a plane normal to its own longitudinal axis, and a tool mounting arm 27 rotatably supported on the column. Pneumatic stepper motors 15, 25, 29, or actuators are provided for displacing the column relative to the support frame, for rotating the mounting arm relative to the column, and for adjusting the height of the column so as to enable a tool mounted on the arm to be positioned at a point specified in three dimensions. Preferably the device is for use in disposing of an unexploded munition. The tool may be used to direct a high pressure jet of water carrying particles of a hard abrasive, such as garnet, divine or alumina.

Description

Tool Manipulating Device The present invention relates to a device for manipulating a tool, such as a cutting tool, by remote control in relation to a workpiece.

Background of the invention One way of disposing of an unexploded munition involves cutting through its casing using a tool which directs at the casing a high pressure jet of water carrying particles of a hard abrasive such as garnet, olivine or alumina. Such a tool can rapidly cut into the casing and, as water is used for the cutting, little heat is generated. Once a large hole has been cut in the casing, the explosive can be burned or washed away safely without risk of an explosion as a high pressure can no longer build up within the casing.

In carrying out this process, it is necessary to guide the cutting tool to trace a closed path over the surface of the casing while maintaining the tool at a controlled distance from the surface. This task cannot of course be done by hand because of the risk that the munition might explode and because the liquid jet used for cutting would itself presents a serious danger to the operator.

There is therefore a need for a manipulating device that can be controlled remotely and can accurately position the cutting tool to follow a desired path relative to the munition, the path being specified in three dimensions.

This particular application places additional requirements on the positioning device. For example, it is deemed unacceptable for the manipulating device to straddle the munition because its initial installation over the munition would be fraught with danger.

It is also important that the manipulating device should not have any form of magnetic field associated with it that would trigger certain types of magnetically influenced fuze.

Summary of the invention With a view to enabling the foregoing requirements to be met, the present invention provides a device for manipulating a tool relative to a workpiece, which device comprises a support frame, a column movable relative to the support frame in a plane normal to its own longitudinal axis, a tool mounting arm rotatably supported on the column, and pneumatic stepper motors or actuators for displacing the column relative to the support frame, for rotating the mounting arm relative to the column and for adjusting the height of the column so as to enable a tool mounted on the arm to be positioned at a point specified in three dimensions.

Pneumatic stepper motors are known and may for example comprise three piston/cylinder units or jacks that are disposed radially in relation to an output shaft and the pistons of which act directly on a roller bearing mounted on an offset crank of the output shaft. When air pressure is applied to two jacks while the third jack is connected to atmosphere, the crank will move into a position where it lies in line with the third cylinder and the piston of that cylinder will be in the position corresponding to the minimum volume of its working chamber. By switching the pressure connections to the jacks so that a different pair of jacks is pressurised, the crank can be moved in either direction by 1200. The motor acts as a stepper motor in that each switching of the connections of the pressure lines leading to the jacks will result in a fixed incremental movement of 1200 and no further movement will occur until the pressure connections are again changed. Of course, the

detailed construction of the air stepper motors may differ from that described in that the pistons could, for example, be connected to different cranks by means of connecting rods in a configuration reminiscent of early aircraft engines.

The use of pneumatic stepper motors in a positioning device intended for use in the disposal of munitions gives rise to several important advantages. Unlike electric motors, pneumatic motors can be made entirely from nonferrous materials and they do not rely on electric controls signals which could themselves produce magnetic fields, electric fields and sparks that risk detonating the munition.

Furthermore, unlike hydraulic jacks, pneumatic motors require only one supply line. As the positioning device will normally be arranged at some distance from its source of power, in this case an air compressor, this results in easier setting up and an important reduction in the bulk of the equipment that has to be carried to the site of the munition.

Pneumatic stepper motors produce significant output torque, especially if they are used to drive the support column and the mounting arm through gearboxes. They nevertheless do not consume much power and in this respect they offer an important advantage over the use of air turbine motors where a considerable mass or air must flow past the turbine to produce the necessary torque.

A still further advantage stems from the incremental movement of the motor which can considerably simplify the control system as it permits open loop control of the motors.

It is preferred that the mounting arm should have at its end a wrist to enable the inclination of the tool to be adjusted relative to the mounting arm.

A munition typically has a cylindrical casing and the manipulating device will in use normally be arranged such that the column lies to one side of the casing so that it may be moved towards and away from the axis of the casing as well as parallel to the axis of the casing. Altering the height of the column on which the tool arm is mounted can then be used to set the distance of the tool from the casing of the munition. By moving the column in two dimensions and altering its length in the third dimension, the tool can be made to trace a closed path on the surface of the casing to cut a hole in the munition, while being disposed entirely to one side or near one of the axial ends of the casing.

To control the manipulating device, it is possible to position the tool by manual control (while it is inoperative) at reference points along the desired path and then to rely on the control system to interpolate between the selected reference point in order to plot the position of the tool at every point along the desired path. The tool can then be powered and left to cut the munition automatically while personnel withdraw to a safe distance.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a manipulating device of the invention positioned to one side of a munition resting on the ground, Figure 2 is a front view of the manipulating device, and

Figure 3 is a schematic axial section through a pneumatic stepper motor.

Detailed description of the preferred embodiment The manipulating device shown in Figures 1 and 2 comprises a frame 12 having four sides designated 12a to 12d. The frame is supported on the ground at an angle to the by means of legs 13 and in use is set up to stand to one side of an unexploded munition without straddling it.

A carriage 14 is movable along the sides 12a and 12b in the direction of the arrow 16 by means of a pneumatic stepper motor 15. The motor 15 in the illustrated embodiment is mounted on the frame 12 and rotates shafts 19 in threaded engagement with nuts 21 mounted on the carriage 14. As an alternative, a transmission system comprising a toothed belt, or wires guided about pulleys and wound about a drum driven by the motor could be employed. Numerous such transmissions are disclosed in the prior art and a detailed description of the drive connecting the motor to the carriage is not believed to be necessary as several viable possibilities will present themselves to the person skilled in the art.

A column 18 is mounted on the carriage 14 for movement in the direction represented by the arrow 20. A pneumatic stepper motor 25 is used to move the column 18 relative to the carriage 14 and once again a variety of transmission systems can be employed.

The column 18 is itself adjustable in height by means of a pneumatic ratchet mechanism or other suitable pneumatic actuator and carries at its free end an arm 27 which can be rotated through 3600 by means of a further motor 29. At its end, the arm 27 supports a tool holder 31 and the latter can be pivoted relative to the arm 29. The arm 29 can be moved

manually to set the radial distance between the tool holder 31 and the axis of the column and the angle between the tool holder 31 and the arm 29 can also be preset manually.

The tool holder 31 is designed to grip a tool in the form of a nozzle from which there is emitted a high pressure jet of water containing a suspension of an abrasive powder or grit such as garnet, olivine or alumina. In use, the jet is aimed at the surface of the munition and, using the various pneumatic motors and actuators, the jet is made to trace a desired closed path over the surface of the munition to cut a hole in its casing. The distance of the tool from the surface of the munition and the attitude of the tool can all be controlled for efficient and accurate cutting.

As previously noted, a first important feature of the manipulating device is that it is not placed over the munition and does not straddle it but just stands next to it and aims a jet of water at it. The other important feature is that the motors are pneumatic stepper motors, an example of which will be described below with reference to Figure 2.

Such pneumatic stepper motors and their gearboxes can be made of non-ferrous materials, such as aluminium or titanium, so that the entire positioning mechanism may be non-magnetic and not connected to any form of electrical supply.

The pneumatic stepper motor 50 shown in Figure 3 has three pistons 52a, 52b and 52c reciprocably mounted in cylinders 54a, 54b and 54c that are formed radially in an annular block 56. The working chambers 58a, 58b and 58c of the three piston/cylinder units or jacks are connected by way of respective connectors 60a, 60b and 60c to respective air lines that can individually be connected to a suitable system of valves either to a source of compressed air or vented to ambient atmosphere.

The radially inner ends of the pistons 52 act on a bearing 62 that is fitted to an eccentric crank on an output shaft of the motor. The shaft cannot be seen in Figure 2 but it rotates about the axis 64 while the cross 66 in the drawing indicated the centre of the crank and the bearing 62.

If pressure is applied to the working chambers 58a and 58b and the working chamber 58c is vented to atmosphere, the bearing 62 will be moved by the air pressure to the illustrated position in which the piston 52c is fully retracted into its cylinder bore. If in this position, pressure is supplied to the working chamber 58c while the working chamber 58b is vented, the crank will rotate the output shaft clockwise until the bearing is in line with the axis of the piston 52b. After this incremental movement, the output shaft will come to a stop until the next commutation of the pressure in the supply lines leading to the three working chambers. It will be noted that the output shaft could have been made to rotate counter clockwise by venting the working chamber 58a instead of the working chamber 58b so that the motor output shaft can be moved in fixed increments in either direction.

Because the motors all move in fixed increments, it is possible to use open loop control in setting the position of the tool but it is also possible to use closed loop control if preferred. In this case, optical transducers can be used to sense the actual position of the carriage 14, the column 18, the arm 22 and the tool holder 26.

In use, there will be typically several stations at which equipment is disposed. Furthest from the munition, there will be an engine driven generator to provide compressed air, high pressure water and electrical power.

Nearer to the munition will be pneumatic controls, the mixing station of the abrasive with the water, and the

connections for the remotely sited command and remote control centre. High pressure water mix (water and abrasive) and compressed airlines lead from the second station to the cutting tool manipulating device.

At first, an operative places the cutting tool and its manipulating device next to the munition and plots relative to the munition the outline of the hole that is to be cut.

Prior to commencement, the position of the arm 29 and the attitude of the tool holder 31 are set to suit the nature of the cut. If, for example, the nose at the front of the munition is exposed, the axis of the column could be pointed along the axis of the munition and the arm 27 is simply rotated through 3600 while the tool holder is aimed to cut an inwardly tapering cone. The size of the hole can then be determined by the radial distance of the tool holder 31 from the axis of rotation of the arm 27. If, as is more often the case, the nose is partially buried in the ground, then a desired path for cutting is marked out on the cylindrical surface of the munition, as shown in Figure 1, and the tool holder is set for the tool to be as near perpendicular to the surface of the munition as possible.

The entire operation of rendering the munition harmless is thereafter controlled from a safe distance relying on television cameras pointed at the munition to monitor the operation. Using manual controls and/or feedback from the television cameras, the tool is positioned by an operative at points that correspond to cusps or turning points in all three dimensions and these are then entered in the control program of the tool as reference points. The control program plots all the points along the desired path by interpolating between the reference points. After the high pressure water mix has been turned on, the tool is moved automatically by the control program under open or closed loop control until a hole is cut in the casing of the munition thereby preventing it from exploding. The

explosive within the munition can now either be burned safely or washed out of the casing to render the munition harmless.

Claims

CLAIMS 1. A device for manipulating a tool relative to a workpiece, which device comprises a support frame, a column movable relative to the support frame in a plane normal to its own longitudinal axis, a tool mounting arm rotatably supported on the column, and pneumatic stepper motors or actuators for displacing the column relative to the support frame, for rotating the mounting arm relative to the column and for adjusting the height of the column so as to enable a tool mounted on the arm to be positioned at a point specified in three dimensions.
2. A device as claimed in claim 1, wherein the mounting arm has at its end a tool holder and the mounting arm is mounted on the column in such a manner as to allow the radial distance of the tool holder from the axis of rotation of the arm to be adjusted.
3. A device as claimed in claim 2, wherein the tool holder is pivotably supported on the mounting arm to enable the angle between the tool holder and the axis of the mounting arm to be adjusted.
4. A device as claimed in any preceding claim, wherein the components of the device are made of a nonferromagnetic material to enable the device to have a low magnetic signature.
5. A device as claimed in any preceding claim, which comprises no electric motors or actuators and supports no electrical circuitry, so as to enable the device to have a low electric signature.
6. A device for positioning a tool relative to a workpiece substantially as herein described with reference to and as illustrated in the accompanying drawings.