GB2354752A - Material handling arm - Google Patents

Abstract

A generally vertically arranged apparatus 10 for remotely manipulating radioactive material is provided. The apparatus consists of a two sectioned arm 26 with an end effector 42 on the lowest end, and a means 28 for suspension from a support structure 20 on the highest end. Four artificial muscle actuators 30, 32 (34, 36, Fig 3) in a cruciform arrangement are used to manoeuver the apparatus. The two sections are flexibly joined mid way and the lower section is extendable by means of a cylinder 40. Preferably, the apparatus is remotely controlled via a camera (70, fig 5), monitor (102, fig 5) joystick and microprocessor.

Description

2354752 APPARATUS FOR REMOTE HANDLING The present invention relates to

apparatus for remotely handling particularly, though not exclusively, hazardous material such as nuclear waste.

The nuclear industry generates a great deal of waste 10 resulting from the generation of power, for example, from the nuclear fuel cycle. After several years in a nuclear reactor, the fuel becomes less efficient and must be removed and replaced with fresh fuel. The irradiated fuel is generally reprocessed to separate the unused uranium and plutonium by-product, the waste being treated and stored. The irradiated fuel is generally stored in socalled cooling ponds at the reactor site for a period of time such as about 100 days minimum prior to transporting to a reprocessing facility. Nuclear reactors have been in constant use in the United Kingdom since 1956 and for nearly as long in some other countries. As a result of the storage of irradiated fuel in cooling ponds over this period of time, debris and silt have built up in these water-filled ponds which must eventually be removed and treated. Some of the earliest fuel was the so-called "Magnox" fuel which was uranium fuel encased in a can made of a magnesium alloy known as Magnox (trade name).

As stated above, storage of irradiated fuel was frequently underwater in cooling ponds, the water acting as an initial level of radiation screening. The I irradiated uranium fuel was sometimes removed from the canning material underwater thus, resulting in the ponds becoming filled with debris from the de-canning operations and general miscellaneous debris collected over the years. As part of a continuing clean-up process, all of the debris must eventually be removed and transferred to a reprocessing facility for treatment and safely storing for the future.

Current water-filled storage ponds are about 2 to 4m square and about 6m deep with a depth of water of about 5m therein. Presently, some ponds have up to 1.75m of debris in the bottom from old Magnox canning material and other radioactive debris. A further disadvantage of the accumulated debris in the ponds is that many ponds are linked by underwater tunnels having a rail track running through to a plant for reprocessing or for storage. Thus, the debris prevents the smooth operation of the transport facility which has skips running on the rails.

As with many older facilities, little provision was made at the time of building for automated handling of nuclear waste. The current method of manipulating the debris from the ponds into skips for removal is by human man- handling. The ponds have guard rails therearound of approximately 1.3m in height. Operators working over these guard rails manipulate stainless steel poles of 7.5m in length and which weigh 15kg. At the remote end of the poles there are options on mechanical attachments including pneumatic tongs to grasp the debris and hydraulic clamps to cut and crush and size reduce the 2 debris before being loaded into skips for underwater transport to the reprocessing facility. At present the operators are required to manoeuvre the pole with attached tongs to a position above the fuel or other debris, before grasping the target material by means of foot operated pneumatic tongs. At this stage the waste, which may weigh up to 20kg in addition to the weight of the pole, must be lifted and placed in the transport skip. Other debris on the floor of the pond may require that the retrieved material must be moved vertically up to 2m to be free of entanglement. To prevent jamming of the waste in the removal skip, pieces of waste must not be bigger than lm. During movement of waste within the pond as described above, silt within the pond is disturbed resulting in reduced visibility. Reduction in visibility may mean that clearing operations have to be suspended until the silt settles again.

The retrieval and clean-up process described above means that the operators must wear respirators and full PVC protective suits. For workers operating under these conditions, there are a number of hazards which include:

high radiation levels meaning that workers can only work for about 1.5 hours/day so as to remain within permitted radiation dosage levels; the task involves heavy manual work which is very tiring and hot within the protective suits; the heavy nature of the work can lead to physical injury such as back strain; and, the heavy loads mean that the operations are slow and accuracy, if needed, is low.

3 To put the scale of the problem in context, the clean-up of one set of storage ponds at one nuclear facility within the UK is part of a continuing 20 year program.

Various remotely controlled hydraulic apparatus for manipulating the waste has been proposed but such apparatus is expensive and unreliable. Similarly, robotic manipulators have been proposed but these are unreliable when used underwater and prone to contamination from the radioactive debris which makes them difficult to repair easily and are also expensive.

It is an object of the present invention toprovide apparatus which allows the remote handling and manipulation of hazardous debris which apparatus is accurate and reliable in operation and is also relatively inexpensive compared with the hydraulic systems proposed in the past.

According to the present invention, there is provided apparatus for the handling of material, the apparatus comprising: manoeuvrable material contacting arm means; two pairs of synthetic muscle actuator means operably connected to said arm means so as to determine the position of said arm means; and, a control system allowing control of the position of said arm means via control of said two pairs of synthetic muscle actuators.

Whilst the apparatus of the present invention is 30 primarily intended for the remote handling of hazardous waste such as radioactive waste for example, it may also 4 be used for the handling of any material which it is capable of lifting and moving. Thus, the definition of the term "material" must be widely construed.

The "synthetic muscle actuator" means are described in more detail below and may be actuated by inflation by either hydraulic or pneumatic means. Pneumatic actuation means are preferred since the equipment necessary for pneumatic actuation is much more economic and easier to use than are hydraulic means.

So-called "pneumatic muscle actuator" (pMA) devices comprise an inflatable bladder of flexible material such as an elastomer for example, the inflatable bladder being surrounded by an outer sleeve of a material which is substantially longitudinally inexpansible under normal loads but is radially expandable. The ends of the bladder and the sleeve are connected to each other. Expansion of the bladder causes radial expansion of the sleeve and consequential shortening thereof thus, exerting a pulling force on anything to which the device is connected. The radially expandable outer sleeve may, for example, comprise a sleeve of braided nylon fibres or filaments or an elastomeric sleeve having longitudinally embedded fibres therein, for example, allowing radial expansion of the sleeve but not longitudinal extension.

A typical example of a synthetic muscle actuator is as described in US-A5 351 602.

Since quite large movements of the arm means are required to be made, it is necessary that the means of moving the arm are capable of the required large displacements. For example, a pond over which the apparatus may be sited may be about 3m square. It is necessary for the end of the arm means to be able to extend into the corners of a rectangular pond thus, in this instance, a displacement approaching 2m in each direction about a central neutral point is needed. One important advantage of synthetic muscle actuators not appreciated by the prior art is that they may be made in virtually any length required. The achievable displacement is typically 30-35% of the dilated length.

Pneumatic muscle actuators can operate safely in aquatic or other liquid environments and are safe in explosive gaseous environments.

The manoeuvrable material contacting arm means may be suspended at one end from a supporting structure or cradle placed over the area where material handling is required. The arm means may be suspended by a suitable joint such as a spherical bearing, for example, so as to allow freedom of movement in 2 axes about the joint. In one embodiment of apparatus according to the present invention, the supporting structure may be simply constructed of scaffolding poles and clamps.

Each of the synthetic muscle actuators may be connected 30 at one of their ends to the arm means intermediate its ends. In plan view the four actuators may form a 6 cruciform arrangement. The other ends of the actuators may be connected to the supporting structure for example or to other suitable anchor points such as on the walls of a pond, or other supports, over which the apparatus of 5 the present invention is placed.

The arm means may alternatively be jointed and have two constituent members which allows additional flexibility of manoeuvre. The arm may have, for example, a first arm member which is connected to a support structure by means which allows rotational movement with respect to a generally vertical axis and, a second arm member connected to the first member by a suitable joint to allow the second member to be height positionable with respect to a horizontal axis. Control of rotation may be effected by pMAs acting on the second arm member through a relatively simple mechanical linkage for example and, control of height position may be effected by pMAs acting on the second arm member disposed about the joint position by which it is connected to the first arm member.

The end of the arm means remote from the supported end or ends may be provided with suitable remotely actuated grab or pincer means to enable material to be handled, reduced, cut or moved for example.

The arm means may a1so be provided with means to enable the length thereof to be changed. Such length changing means may include for example a pneumatic or hydraulic cylinder and suitable actuation means to allow extension 7 or contraction, for example, of the arm means in the general direction of the arms means. However, any suitable mechanically, pneumatically or hydraulically controlled or actuated linkage on the arm means may be employed alternatively or in addition to the cylinder means described above to achieve control of the length of the arm means.

The apparatus of the present invention, where hazardous 10 material is to manipulated, may have a control system which enables the movements of the arm means to be controlled from a remote site. In embodiments of the present invention, the movement of the arm means may be viewed by a camera situated in close proximity to the arm means giving direct visual feedback to the operator of the arm position which may be controlled by means of a joystick directly moved by an operator giving analogous positional to the actual arm per se. The camera may be placed in any suitable position to give an optimum view of the arm means.

A particular advantage of the apparatus according to the present invention is that it is easily manufactured and relatively very low cost. Therefore, if the apparatus is contaminated or damaged, it can be disposed of in the same way as the waste which it is being used to handle. Conventional robots are too expensive to contemplate disposal if they are damaged or contaminated and generally have to be repaired or decontaminated which adds to costs.

8 In order that the present invention may be more fully understood, an example will now be described by way of illustration only with reference to the accompanying drawings, of which:

Figures 1A and 1B show a schematic elevation and plan view respectively of apparatus according to the present invention arranged over a pond containing hazardous waste; Figure 2 shows an axial cross section through a schematic pneumatic muscle actuator as employed in the present invention; Figure 3 shows a schematic plan view of the arrangement of pneumatic muscle actuators and the geometrical interrelationships for explaining the operation of the apparatus and control system; Figure 4 shows a schematic plan view of the arm means and pMAs of Figs.1 and 2 at a maximum displacement; Figure 5 shows a schematic arrangement showing the apparatus including the control system elements of the 25 present invention; Figure 6 shows a flow diagram corresponding to the apparatus arrangement shown in Fig.5; 9 Figure 7 shows a flow diagram indicating the class hierarchy of the software used to control the actuation of the arm means; Figure 8 shows a schematic diagram of the control system for each antagonistic pair of pMAs; and Figure 9 which shows a schematic arrangement in elevation of a second embodiment of handling apparatus according to the present invention.

Referring now to the drawings and where the same features are denoted by common reference numerals.

Apparatus according to the present invention is depicted generally at 10. The apparatus 10 is sited over a pond 12 containing waste (not shown) submerged in water and sits on a base plate 14 which lies on the ground 16 over the edge 18 of the pond. The apparatus 10 comprises: a support structure 20 built of well-known scaffold poles and brackets 22 rising to an apex 24; an elongate waste material contacting and manoeuvring arm 26 suspended from a spherical bearing 28 held at the apex 24 of the support structure 20; and, four pMAs 30, 32, 34, 36 each connected between the arm 26 at the point "Y" and the support structure 20. It is to be noted that the base plate 14 is not necessary to the invention as the support structure 20 may be made of sufficient size as to sit directly on the ground 16 surrounding the mouth of the pond 12. The arm 26 is provided with a pneumatic cylinder 40 to enable the length thereof to be extended or retracted as desired and suitable means 42 for gripping, cutting or otherwise holding or treating waste. The cylinder 40 and gripping means are controlled by suitable services (not shown) running along the arm 26 and operated remotely as will be described below.

In the embodiment shown, the mouth of the pond 12 is 3m square and the length of the arm is 7. 5m to the bottom 50 of the pond.

Figure 2 shows an axial cross section of a schematic pMA indicated generally at 30 and is of the type as employed in the apparatus shown at 10 and is substantially the same as the other pMAs 32, 34 and 36. The pMA 30 is constructed as a flexible two-layered cylinder comprising an inner rubber liner 60, an outer containment layer 62 of braided nylon and end caps 64, 66 that seal the open ends of the liner 60. The end caps 64, 66 are firmly fixed to the ends of the liner 60 and the outer containment layer 62 by clamp rings 68, 69. The pMAs also have fixings 72, 74 on the end caps to enable the pMA to be attached between two fixing points. One end cap 64 has an inlet/outlet port 76 for inflation/deflation thereof.

Inflation of the liner 60 up to the maximum permitted by the outer containment layer 62 causes the ends of the pMA to be drawn towards each other, i.e. causing a contraction in the length of the pMA. The pMAs as used in the embodiment described herein are each about 4m in length and have an inflated diameter of 70mm. Two pMAs in antagonistic array are able to achieve a displacement range of about 0. 5m. The workspace at the tip of the I I 7.5m long arm 26, i.e. at the bottom of the pool 12 is about 3m x 3m thus with the pMAs mounted at point "Y" which is 1.5m from the bearing 28, the necessary displacement is achieved.

The control system employs draw-wire position sensors indicated schematically in Figure 3 at 150, 152 and which are fixed at one end to the pMA intermediate its ends at "E" and "E" and at the other end to the arm 26 at the position Y" (coincident with the muscle actuator attachment points on the arm). In this case the two sensors are connected between points "FY" and "EY" and are used to measure the position of the arm 26 and form a closed loop feed back path. The pMAs are arranged as two pairs 30, 32 and 34, 36 in antagonistic disposition against each other, i.e. as pMA 30 dilates, pMA 32 contracts in length due to radial inflation of the bladder therein and vice versa, and similarly for the pair 34, 36. Dilation and contraction is automatically controlled by a pneumatic valve system which is operated by a feedback loop in response to positional signals from an arm position controller. The control system will be described in more detail below.

Direct viewing of the lower tip of the arm 26 and the grab 42 is effected by a CCD camera 70 which may be mounted in any suitable location which enables adequate viewing of the working area and manipulating arm.

As may be seen from the flow chart of Figure 6 and the schematic arrangement of Figure 5, control of the 12 position of the arm tip and grab 42 is effected by a human operator 80 directly manipulating an inverted 2axis joystick controller 82. Use of an inverted joystick controller is used so as to mimic to as great an extent as possible the actual movements of the arm 26 so as to make control of the arm movements and position as intuitive as possible. The outputs from the joystick controller are fed into a control computer 84 through an analogue to digital converter (ADC) card 86. The computer 84 controls the operation of a servo controller 88, via a digital to analogue converter 160, which operates air valves (indicated only schematically at 90, 92, 94, 96 in Figure 3) which control the flow of air into and out of the pMAs so as to effect contraction and expansion thereof. The valves and pMAs are linked to a supply of compressed air 100. In this case the valves are pressure regulating Joucomatic Series 602 (trade name) servovalves driven by a 15OHz pulse width modulated signal with a mark/space ratio set by an external analogue voltage generated by the computer 84. Movements of the arm 26 are viewed by the operator 80 on a monitor 102 remote from the site of the pond 12. Movements of the arm 26, parameters relating to air pressure in the pMAs may be recorded on a chart recorder 104 if desired. 25 Figure 4 shows a reproduction of a display from the monitor 102 showing a plan view of the displacement of the arm 26 which is in addition to a direct, real-time view of the arm movements from the camera 70. In Figure 30 4, the pMAs 32, 34 are at or close to maximum contraction, i.e. at or close to maximum expansion of the 13 liner 60 and the antagonistic pMAs 30, 36 are at or close to maximum dilation, i.e. the liners 60 are deflated. In order to move the arm 26 back towards the centre of the area KLMN, the air in the pMAs 32, 34 is released simultaneously with the liners 60 of the pMAs 30, 36 being inflated.

The control of each antagonistic pair of pMAs is represented in Figure 8 and consists of two loops: an inner proportional integral derivative (PID) loop 120, 122 to control pressure in each pMA and an outer PID loop 124 to control the position of the arm 26 tip in cartesian space. To compensate for hysteresis effects in the valves 90 to 96 during venting of the pMAs and to make inflation/deflation of the pMAs as symmetrical as possible, pMA pressure controllers and pressure sensors 128, 130 are used for each pMA pair.

In Figure 3, A, B, C, D are the attachment points of the pMAs on the support structure 20 whilst F and E are the draw-wire sensors 150, 152 mounting points. "b" is the length of the draw-wire sensor at start up and which is constant, and a is the range of displacement achievable by each pMA antagonistic pair. "dl" and "d2" are the lengths of the draw-wire sensors at any instant. As stated above, the draw-wire sensors 150, 152 are attached between the arm 26 at "Y" and at "E" and "F" and the "a by a-" square shown in Figure 3 defines the range of motion of the arm 26 at the connection point "Y". The distances "d1" and "d2" may be calculated by simple equations. Signals relating to the change in length of 14 the draw-wire sensors 150, 152 are fed back to the computer 84 via an analogue to digital converter 162 to form a closed loop control system.

The class hierarchy of the software which controls the operation of the apparatus is schematically indicated in the diagram of Figure 7. The generic class "SENSOR" implements a sensor object. The classes "Pressure Sensor" and "Position Sensor"' hold the readings from the pressure sensors 128, 130 and from the position sensors 150, 152 and provide any calibration needed. The digital to analogue converter, "DAC", class provides access to the data acquisition board of the computer 84, whilst the "INPUT DEVICE" provides access to the system input device, i.e. the joystick 82. The "USER INTERFACE" class implements the interface between the operator 80 and the system providing a range of options including initialising the system, tuning the position and pressure sensor controllers, and calibrating the joystick. The "CONTROLLER" class implements the control scheme of the system, using as inputs the values from the sensors, the joystick device and the controller settings. The "ARM" class provides the structure for storing all the arm data including the position of the arm tip and the pressure in the pMAs. The "ARM" class also communicates with the hardware of the system to execute the commands coming from the "CONTROLLER" class whilst the "DISPLAY" class is responsible for displaying relevant operating parameters to the operator 80 on the monitor 102.

Since the joystick controller 82 may be moved faster than the arm 26 can respond, a low pass filter is incorporated into the system to prevent the arm from becoming oscillatory.

Figure 9 shows a schematic view in elevation of a second embodiment of apparatus according to the present invention. This second embodiment does not have two pairs of pMAs working in antagonistic array directly on the arm to be manoeuvred. In this embodiment the manipulating arm which extends into the pond 12 is in two parts; a first, upper arm part 200 and, a second, lower arm part 202 jointed to the lower end of the upper arm 200 at a bearing 204. Elevation of the lower arm 202 (and the grab means 42) is controlled by a pair of pMAs 210, 212 connected between a top fixing on a bearing 214 and at points 216, 218 respectively on either side of the pivot bearing 204. The upper end of the upper arm member 200 is suspended from the bearing 214 which enables both the arm members 200, 202 to be rotated about a vertical axis 220.

Rotation of the arm assembly is effected by a second pair of pMAs 230, 232 which operate cables 234, 236 via pulley and lever arrangements 240, 242. The length of the lower arm 202 may be controlled by a pneumatic cylinder 40.

Movement of the upper and lower arm members, and also of the arm length, may be detected by draw-wire sensors as in the first embodiment described above or by shaft encoders in the bearings 204, 214, for example. The control system may be essentially similar to that described above where signals from a remote sending device such as joystick are fed to a computer and signals 16 from the sensors or encoders may be fed back to the computer to form a closed loop control system. The pMAs may be controlled by the same types of valves and servo controllers as described hereinbefore with reference to the first embodiment and as would be understood by the person normally skilled in the art.

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Claims (21)

1. Apparatus for the handling of material, the apparatus comprising: manoeuvrable material contacting arm means; two pairs of synthetic muscle actuator means operably connected to said arm means so as to determine the position of said arm means; and, a control system allowing control of the position of said arm means via control of said two pairs of synthetic muscle actuators.

2. Apparatus according to claim 1 wherein the synthetic muscle actuator means are pneumatically operated.

3. Apparatus according to claim 1 wherein the synthetic muscle actuator means are hydraulically operated.

4. Apparatus according to claim I wherein the manoeuvrable material contacting arm means is suspended at one end from a supporting structure placed over the area where material handling is required.

5. Apparatus according to claim 1 wherein the arm means is suspended from a spherical bearing.

6. Apparatus according to claim 1 wherein each of the synthetic muscle actuators is connected at one of their ends to the arm means intermediate the ends of the arm means.

7. Apparatus according to claim 1 wherein in plan view the four synthetic muscle actuators form a cruciform arrangement.

8. Apparatus according to claim 4 wherein the other ends of the actuators are connected to the supporting cradle.

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9. Apparatus according to claim 4 wherein one end of the arm means remote from the supported end is provided with remotely actuated grab or pincer means to enable material to be handled, reduced, cut or moved.

10. Apparatus according to claim 1 wherein the arm means is provided with means to enable the length thereof to be changed.

11. Apparatus according to claim 10 wherein the means to change the length of the arm means is a pneumatic or hydraulic cylinder.

12. Apparatus according to claim 1 wherein the control system enables the arm means to be controlled from a remote site.

Apparatus according to claim 1 wherein the movement of the arm means is viewed by a camera situated in close proximity to the arm means giving direct visual feedback to the operator of the arm position.

14. Apparatus according to claim 13 wherein the position of the arm means is controlled by a joystick directly moved by an operator.

15. Apparatus for the handling of material, the apparatus comprising: manoeuvrable material contacting arm means; two pairs of synthetic muscle actuator means operably connected to said arm means so as to determine the position of said arm means; and, a control system allowing control of the position of said arm means via control of said two pairs of synthetic muscle actuators wherein said arm means comprises an upper and a lower arm member jointed together.

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16. Apparatus according to claim 15 wherein said upper arm member is held in a generally vertical direction and is arranged for rotation about a generally vertical axis.

17. Apparatus according to claim 16 wherein rotation is effected by a pair of pneumatic muscle actuators acting via a mechanical linkage.

18. Apparatus according to claim 15 wherein said lower arm member is arranged for vertical movement with respect to a generally horizontal axis.

19. Apparatus according to claim 18 wherein said vertical movement is effected by a pair of pneumatic muscle actuators disposed about a pivot on said lower arm member.

20. Apparatus according to claim 15 wherein said lower arm member further includes means to enable the length thereof to be controlled.

21. Apparatus according to claim 20 wherein said length controlling means comprises a pneumatic cylinder.