GB1594577A

GB1594577A - Control apparatus

Info

Publication number: GB1594577A
Application number: GB4820676A
Authority: GB
Original assignee: Herga Electric Ltd
Current assignee: Herga Electric Ltd
Priority date: 1978-02-03
Filing date: 1978-02-03
Publication date: 1981-07-30

Description

(54) CONTROL APPARATUS (71) We, HERGA ELECTRIC LIMITED, a British Company of Northern Way, Bury St. Edmunds, Suffolk IP32 6NN, England do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a control apparatus comprising a fluid filled conduit which can be restricted at at least one and preferably various positions along its length (e.g. by squeezing it) and a sensing device which produces a control signal when the conduit is restricted as aforesaid.

One such device is described in U.K.

patent specification 1,060,488 and comprises a flexible conduit which is fixed to one vertical edge of the power driven door. The conduit contains a stationary column of air which communicates with a pressure sensitive swtich. When the door is closing and meets an obstruction, the latter compresses the conduit thereby decreasing the volume of air, and so increasing the pressure, inside it. The increase in pressure operates the switch which prevents the door from closing further. A generally similar device is described in U. K. patent specification No. 1,422,932.

A disadvantage of such known systems is that the increase in pressure caused by the compression of the conduit over a short part of the length thereof does not provide a large pressure difference. This can be a problem since small pressure differences are relatively difficult to sense accuratelv.

Also, because the pressure sensor needs to be very sensitive it can be subject to false actuation.

By employing this invention it is possible to eliminate, or at least reduce the severity of these problems.

This invention provides control apparatus comprising: a conduit which can be restricted at at least one position along its length; means for causing a flow of fluid in the conduit; and a sensor which responds to a variation in the flow, caused by restriction of the conduit, to produce a control signal.

The signal can take any form and can for example be an electrical, optical, hydraulic or pneumatic signal or a mechanical movement.

The conduit may be flexible so that distortion thereof restricts the fluid flow.

Preferably the whole circumference of the conduit at the selected point is flexible. A number of flexible portions may be included or the conduit may comprise a flexible portion of substantial length so that constriction of the conduit can be achieved at any one of a number of consecutive points.

Preferably the fluid used is air. The means for causing fluid flow in said conduit may comprise a blower, or a variable volume fluid actuator, such as a piston and cylinder device or a flexible walled bellows.

Such means may be operative to cause fluid flow 1either by creating super-atmospheric pressure or sub-atmospheric pressure. In one preferred. form the means may comprise a reservoir containing air at superatmospheric pressure or at sub-atmospheric pressure, i.e. a partial vacuum. One sensor or more than one sensor may be provided.

Preferably the or each sensor is in the form of a pressure sensitive electric switch, so that the signal produced is an electric signal.

The invention has a variety of applications. For example, it may be embodied in a pressure sensitive mat, in which case the conduit may be arranged to be constricted in response to pressure applied to the mat, as by a person stepping upon it. In another example, the invention may be applied to a safety device for switching off a machine in response to a predetermined condition, such as the lifting of a guard or the engagement of a moving part, e.g. a power driven door, into contact with an obstruction.

The invention will now be particularly described. by way of example with reference to the accompanying drawings, in which: Figure 1 illustrates diagrammatically an embodiment of the invention in a pressure sensitive mat; Figure 2 is a graph of pressure against distance along a conduit shown in Figure 1; Figure 3 is a diagram showing an electrical circuit which may be used in combination with the embodiment of Figure 1; Figure 4 is a diagram showing an alternative electric circuit, which may be used in a modification of the embodiment of Figure 1; Figure 5 is a plan view showing a preferred arrangement of a conduit and a means for constricting the conduit, according to a further embodiment of the invention; Figure 6 is a cross-sectional view of the conduit in an alternative embodiment of the invention and shows means for constricting the conduit;; Figure 7 is a section on the line VI-VI of Figure 6; and Figure 8 is a perspective view of the conduit, shown partly broken away.

With reference to Figure 1, an electrically driven air blower is contained in a box 2.

The blower 1 draws air in through its inlet la and supplies it, through its outlet lb, to one end part 3a of a conduit comprising a length of flexible, for example rubber, tubing 3, the other end part 3b of which terminates within the box 2, so that a closed air circuit is formed. The box 2 is provided with an aperture or vent 4, containing a filter 4a, to permit air to enter or leave the closed circuit in response to atmospheric pressure and temperature changes.

The tube 3 includes a portion 3c arranged in a zigzag or sinuous fashion in a pressure sensitive mat shown generally at 5. A sensor in the form of a pressure sensitive electric switch 6 is connected in the inlet part 3a of the conduit and a further sensor in the form of a pressure sensitive switch 7 is connected in the outlet end part 3b. (In alternative embodiments, just one sensor 6 or 7 could be used). In this particular embodiment, an air restrictor 8 is provided in the part 3b.

The restrictor 8 is adjustable, and its purpose is to ensure that the blower develops a pressure greater than atmospheric in the portion of the tube 3 upstream of the restrictor 8. The tube 3 is preferably a relatively small bore tube so that the pressure therealong drops with distance from the blower, as shown by the curve 9 in Figure 2. It will be noted that the portion 9a of the curve, which corresponds to the portion 3c of the tube, has a steeper slope than other portions of the curve 9.

This arises because in the illustrated embodiment the portion 3c of the tube 3 is assumed to have a narrower cross section than the other portions; therefore the pressure drop along the other portions 3a and 3b is less than that along the portion 3c.

However, this is not necessary, and the arrangement could be such that there is a uniform drop in pressure along the tube 3.

As shown in Figure 3, the blower 1 is in series with a start button 10 and a stop button 11. The switches 6 and 7 are also in series with these buttons and with a relay R, the relay R and switches 6 and 7 being in parallel with the blower. A lamp L is in parallel with the relay R, which includes a first contact Rl in parallel with the start button 10, but in series with the blower 1, and a second contact R2 connected in a circuit 12 to be controlled by the mat-5.

When the apparatus is not operating, the switch 7 and contacts Rl and R2 are open, but the switch 6 is closed. Also, the start button is open and the stop button is closed.

The pressure within the tubing will be at atmospheric, which corresponds to the horizontal axes of the graph of Figure 2.

When the start button 10 is pressed, to start up the apparatus, power is supplied to the blower I to produce a pressure in the tube 3 as represented by the curve 9. The switch 6 is such that it remains closed at this time its characteristic being represented by the vertical line 6' indicating that the switch 6 does not open, when being subjected to increasing pressure until such pressure reaches a level P4. Although once the pressure P4 has been exceeded and the switch 6 has opened, the switch will remain open on decreasing pressure until the pressure has dropped to a level P3.The characteristics of the switch 7 are indicated in Figure 2 by the line 7' which shows that the switch 7 closes in response to the pressure reaching a level P2, which is less than the level represented by the curve 9 at the position of the switch 7 in the tube 3, and consequently as the pressure builds up in the tube 3 switch 7 will close. Thus, current is supplied to the lamp L and the relay R which causes its contacts RI and R2 to close. When this happens, the start button can be released as the blower will continue to be energised via the contact RI and the relay R will continue to be energised via the contact Rl and switches 6 and 7. The switch 7 is arranged so that when the pressure next falls, it does not again open until it reaches a level P1 which is lower than P2, as shown by the vertical line 7' in Figure 2. Pressure P5 in Figure 2 is representative of the pressure at the outlet lh of the blower and P6 is representative of the pressure at the restrictor 8.

The object of the system illustrated in Figures 1 to 3 is to produce a control signal by opening the circuit 12 in response to compression of the mat 5, as by a person standing upon it, and this operation will now be described. If a person steps on the mat 5, for example at point 13 or point 14 of the portion 3c, a partial or complete blockage of the portion 3c at such points will arise due to squeezing of the tube. This will cause a pressure change in the tube both upstream and downstream of the point at which the blockage or constriction arises. For example, as seen in Figure 2, if a complete constriction is caused at the point 13, the pressure upstream will rise to a level represented by P8, whereas the pressure downstream will drop to atmospheric pressure.On the other hand, if a partial constriction arises, say at point 14, the pressure upstream of point 14 will increase only to the level P7, which is lower than P8, whereas the pressure downstream will drop to a level such as P9, which is above atmospheric pressure.

In either case, since both P7 and P8 are higher than P4, the switch 6 will open; such opening of the switch 6 constituting a first signal. Similarly, the switch 7 will open, since P9 and atmospheric pressure are both lower than pressure P1; such opening of the switch 7 constituting a second signal.

Consequently the relay R will be deenergised so that contact R2 will open (this constituting a third signal) to open the circuit 12, and contact R1 will also open to de-energise the blower. Circuit 12 can only be again closed by repressing the start button.

However the circuit 12 cannot be closed if the start button is pressed while someone is standing on the mat 5, since the switch 7 will remain open and/or the switch 6 will remain open, if already open, or will become open, if closed, so that the relay R cannot be energised.

The system is fail-safe under certain conditions. Consider the possibility that there is a serious leakage in the tube 3 at any point upstream of the restrictor 8, or a permanent blockage. In either of these situations, when the start switch 10 is closed, the switch 7 will fail to close or the switch 6 will fail to open. Thus the relay R and the lamp L will fail to operate, the latter indicating that there is a failure.

A control circuit with increased safety is shown in Figure 4, in which the same reference numbers used previously are used to designate corresponding parts. The arrangement of the air pressure system is the same as illustrated in Figure 1 and 2 except that a further pressure sensitive switch 15 (not shown in Figure 1) is included with the same operating characteristics as switch 7 (i.e. the characteristics represented by the vertical line 7' in Figure 2) and connected to the tube 3 at about the same point as the switch 7. The switches 7 and 15 can be constituted by first and second sets of contacts in a single pressure sensitive switch. Four relays are included.Relay B has two sets of contacts B1 and B2; relay Q has two sets of contacts Q1 and Q2; relay T has three sets of contacts T1 to T3; and relay S has three contacts S1 to S3. Contacts B1 and Ql are in series with the start button 10 and the blower I and are normally open.

Contacts T2 and S2 are normally open and are in parallel with the start button 10.

Contacts Tl and S1 are normally closed and in series with the start button 10 and the relays B and Q, which are in parallel with the blower 1. Contacts Tl and S1 are also in series with the blower 1.

Switch 7 is in series with the relay T and the lamp L1. Relay contacts B2 and Q2 are in series with each other but in parallel with the switch 7 and so arranged that, when the circuit is switched off, the contacts B2 and Q2 do not provide a circuit to the relay T and lamp LI.

Switches 6 and 15 are in series with each other and with the relay S and a further lamp L2.

Relay contacts T3 and S3 are connected in series in the circuit 12. When the circuit of Figure 4 is employed, the system is set into operation by depressing the start button 10 so as to energise the blower 1 and relays B and Q through the normally closed contacts T1 and S1. When the relays B and Q are closed, contacts B1 and Q1 also close and contacts B2 and Q2 each reverse their positions so that they do not provide a conductive path to the relay T and lamp L1.

As pressure builds up in the system, the switches 7 and 15 will close so that the lamps L1 and L2 and the relays T and S are energised so as to close the contacts T2 and S2 (enabling the start button 10 now to be released) and to open the contacts and T1 and Si. Thus, the blower 1 and relays B and Q will now be energised via the contacts T2, S2, B1 and Q1.

Also, when the relays T and S are energised, the contacts T3 and S3 close, to close the circuit 12.

The operation of the circuit of Figure 4 in detecting the presence of a person standing on the mat 5 is similar to that described with reference to Figure 3, i.e. the switches 6 and 7, and also the switch 15, will open. This de energises the relays T and S so that the circuit 12 opens and also the relays B and Q and the blower 1 become de-energised.

Similarly the circuit will be de-energised if a fault, such as a blockage or leakage, arises in the air circuit.

In the event that either of the switches 7 and 15 develops a fault, after the circuit has been switched off, which prevents that switch from operating next time the system is switched on, one or both of the relays T and S cannot become energised to close the circuit 12. If either of the relays B and Q "welds in", jams, or fails to operate, a circuit via the contacts B2 and Q2 will be established to the relay T, which will open the contact T1 thus preventing operation of the blower 1 and subsequent energisation of the relay S when the start button 10 is next depressed.

If either of the relays T and S welds in or jams, the contact T1 or S1 will remain open so that the blower cannot be energised. It either relay T or S fails to operate when power is supplied thereto, contacts T2 and T3 or S2 and S3 will not close.

If a fault does develop in the circuit of Figure 4, the inclusion of the two indicator lamps Ll and L2 assists in locating where the fault has arisen.

Because of the pressure drop along the portion 3c of the flexible tube, this pressure drop being caused by friction, it is desirable to use as short a length of tube as possible whilst still ensuring that it will be constricted by a foot treading on any part of the mat. This can be done by including, as part of the mat, force . transfer means: such force transfer means being adapted to transfer, ~ to one or more localised parts of the tube, pressure exerted by a foot placed on the mat but not directly above any part of the tube. The embodiment of Figure 5 is similar to that of Figure 1 and parts common to Figures 1 and 5 are indicated by identical reference numerals. The figure 5 embodiment includes force transfer means in the form of a piece 15 of expanded metal mesh to the underside of which the tube part 3c is attached by adhesive tape 16.In this embodiment the tube part 3c is arranged in a sinuous pattern, adjacent lengths of which are approximately 350mms apart. Thus a foot could by chance, tread between the tube lengths. In such a situation the pressure applied by the foot would be transferred by the mesh 15 to localised areas of the tube (i.e. areas where the mesh contacts the tube). The bottom of the mat will normally be covered with some suitable flexible sheet 17 and the top with a similar sheet 18 which is shown partly torn away in Figure 1. The edges are trimmed with extruded metal edge strips 19 joined by corner brackets 20. One of these corner brackets 20 acts as a junction between the part 3c of the tube 3 and the parts 3a and 3b which are not part of the mat and are of larger diameter.

Figures 6, 7 and 8 illustrate an alternative embodiment of the invention, in which the system is applied to a so-called "safe edge", for example for a sliding door, to sense the presence of an obstruction to the closing of the door and de-energise the motor which drives the door. The system may of course be applied in other situations, such as around a machine to be protected, or to provide, around a machine, an effectively continuous control enabling the machine to be switched off at any point.

In Figures 6, 7 and 8, a support 21, such as the leading edge of a sliding door, carries a longitudinal open supporting channel 22, for example of aluminium, which contains consecutive runs or portions 23, 24 of the tube 3 of which the remainder and the associated elements such as the blower and the pressure switches are not shown in Figures 6, 7 and 8. The portions 23 and 24 correspond to the portion 3c of Figure 1 in that it is deformation of these portions which is to cause opening of the circuit 12.

A series of retaining members 25 is mounted in the channel 22 so as to hold the tube portions 23 and 24 in the positions shown.

The retaining members 25 include tongue portions 25A disposed between the tube portions 23 and 24 to hold them apart and side portions 25B which project in front of the tube portions 23 and 24 prevent them moving towards the open side of the channel. ~~ A series of force transfer means in the form of pressure applications 26, one applicator between each adjacent pair of members 25, is disposed in the channel 22 and serve to close the open side of the channel. Thus, the supporting channel member 22 and the applicators 26 form in combination, a closed channel containing the flexible conduit. Each applicator includes a base portion 26A having ribs or walls 26B at either end, which ribs 26B engage localised positions of the tube portions 23 and 24 for applying pressure thereto.Lips 22A on the free edges of the channel 22 hold the base portions 26A of the applicators 21 in the channel. Each applicator 26 further includes a lever portion 26C which projects outwardly from the channel. The lever portions 26C are integral with the base portions 26A and one edge of each lever portion 26C is stepped at 26D (Figure 7) so that the edges of the lever portions 26C of adjacent applicators 26 are virtually engaged with each other, whilst nevertheless the base portions of adjacent applicators are spaced apart slightly to accommodate the members 25. Each member 25 includes a recess 25C which is arranged so that the step portions 26D of the applicators do not engage the members 25, which would inhibit movement of the applicators 26 inwardly of the channel. The lever portion 26C can advantageously be of flexible or semi-flexible material, being fixed to relatively rigid base portions 26A.

When used, for example on sliding doors, this allows overtravel to occur, giving time for the door to stop after the protecting system has operated and before the door damages or is damaged by an obstruction.

Compression of the two portions 23 and 24 is achieved either by bodily movement of one or more applicators 26 inwardly of the channel, or by pivotal movement thereof in either direction as indicated by the arrow 27. If pivoting to the left as shown in Figure 8 takes place, the point 28 acts as a fulcrum, and if pivoting to the right takes place, the point 29 acts as a fulcrum. Thus, in the case of a sliding door, if an obstruction is present, preventing closing of the door, bodily movement in the direction of arrow 30 or pivotal movement in the direction of arrow 27 of one or more applicators will take place, compressing the tube and resulting in opening of the circuit -12 in the manner described with reference to Figures I to 3 or 4.

The arrangement of Figures 6, 7 and 8 is intended for providing maximum efficiency in simply closing off the tube portions 24 and 25.

An advantage of the system described is that the presence of electrical conductors in hazardous regions is avoided. In particular, in the case of the embodiment of Figure 1 where a pressure sensitive mat is shown, the system of the invention has the advantage that the mat contains no electrical conductors or electrical connections.

Further isolation from electrical circuitry may be achieved if desired by replacing the switches 6 and 7 by devices which produce a fluidic or other type of pressure signal, or hydraulic signal, in response to pressure changes in the system.

If the blower operates incorrectly, for example by producing too much or too little air, one or more of the switches 6, 7 or 15 will operate in such a way as to prevent the system being energised or will turn the system off.

Although the system shown in the accompanying drawings has been a continually operable system in the sense that the blower 1 produces a continuous flow of air along the tube during operation of the system, this is not essential. If desired, the blower 1 may be replaced by a device producing air flow impulses, for example a variable volume device such as a piston and cylinder or flexible walled bellows. Such a device may operate continuously so that a continuous series of closely spaced pulses are produced. Alternatively the device may operate intermittently so that the air flow impulses are produced only at times when operation of the system is desired.

In this embodiment illustrated, the tube 3 has been flexible, or at least included a relatively long flexible portion or portions, such as the portion 3c or portions 24 and 25.

This is not essential. If desired a mainly rigid tube could be employed with selected portions being flexible, or instead of flexible portions, valves could be included for restricting air flow in the conduit to produce the required pressure changes.

Although the end part 3b of he tube 3 has been shown as connected into the box 2 to provide a closed circuit, this is not essential.

If desired it could be simply left open to atmosphere. However, it is preferred to have a closed air circuit arrangement, so that problems of dirt entering the system may be minimised.

If desired, the air restrictor may be omitted in cases where a sufficient positive or negative pressure, as the case may be, can be created in the system without it.

Although more than one pressure sensitive device 6, 7, 15 has been shown in the embodiments illustrated in the drawings, a system in accordance with the invention could be provided with just a single pressure sensitive means. Such may be in the position of the switch 6 or in the position of the switch 7, as desired, in the case of the embodiment of Figure 1.

However, two or more sensing devices are preferred as this gives added reliability in operation.

Figure 1 illustrates the switches 6, 7 and 15 and the restrictor 8 as being external of the box 2, but these may in fact for convenience all be included within the box 2.

When the system is applied to the edges of elements such as a door, it is not essential to use the arrangement of Figure 6. However, this arrangement is preferred since the applicators 26 provide substantial protection against the risk that the two portions 24 and 25 may become damaged, for example by vandals or by encountering sharp objects obstructing the closing of the door.

The system can be utilised as a device surrounding a machine enabling the machine to be switched off from any point.

The arrangement of Figures 6, 7 and 8 may then be employed: it being understood that pressure applied to any one of the members 26 will stop the machine. Alternatively, a simple flexible tube surrounding the machine may be used, or alternatively constriction of the conduit may be achieved by a series of push buttons at spaced positions around the machine. In this case, the tube may of course be rigid or rigid other than at the points where the push buttons are provided. Where the tube is wholly rigid, the push buttons may be arranged to operate a valve mechanism of some kind.

Further, although in the illustrated embodiment, pressure sensitive switches have been provided to respond to pressure change arising at selected points along the tube 3, it would be possible instead to provide a means for sensing the pressure drop along the selected length of the tube, such as the portion 3c, so that the difference between the pressure at the respective ends of the selected portion is sensed. Means would also be included to produce a control signal, or operate a switch or other device, in response to variation in the sensed pressure difference. With such an arrangement, it is less important that the pressure source should provide a constant output pressure, since variation in the output pressure will, to some extent, not cause corresponding variations in the sensed pressure difference such as to cause production of the control signal etc.

e WHAT WE CLAIM IS: 1. Control apparatus comprising: a conduit which can be restricted at at least one position along its length; means for causing a flow of fluid in the conduit; and a sensor which responds to a variation in the flow, caused by restriction of the conduit, to produce a signal.

2. Control apparatus according to claim 1 in which the conduit is flexible or includes a flexible part so that it can be restricted by applying pressure at the said position.

3. Control apparatus according to claim 1 in which the conduit has a valve by which it is adapted to be restricted.

4. Control apparatus according to claim 1, 2 or 3 in which the sensor is responsive to a pressure change caused by the variation in flow.

5. Control apparatus according to claim 4 in which the sensor is at an upstream end of the conduit and responds to an increase in pressure.

6. Control apparatus according to claim 4 in which the sensor is at a downstream end of the conduit and responds to a decrease in pressure.

7. Control apparatus according to claim 4 including a first sensor at an upstream end of the conduit which responds to an increase in pressure to produce a first signal, and a second sensor at a downstream end of the conduit which responds to a decrease in pressure to produce a second signal.

8. Control apparatus according to claim 7 including means which responds to the first and second signals by producing a third signal.

9. Control apparatus according to claim 4 in which the sensor is responsive to a change in the pressure difference between upstream and downstream ends of the conduit.

10. Control apparatus according to any preceding claim in which the conduit is a flexible tube; the apparatus including force transfer means by which the conduit is adapted to be restricted at a localised position along its length.

11. Control apparatus according to any preceding claim in which the conduit is incorporated as part of a pressure sensitive mat.

12. Control apparatus according to claim II when dependent on claim 10 in which the load transfer means includes an expanded metal sheet.

13. Control apparatus according to claim 11 when dependent on claim 10 in which the conduit extends sinuously within the mat and the load transfer means includes bars each of which extends over parallel lengths of the sinuous conduit in the mat.

14. Control apparatus according to claim 10 in which the conduit extends along a longitudinal support and in- which the force transfer means includes a number of individual elements arranged along the support, each element having a portion in contact with the conduit so that pressure applied to the said element is transmitted to and squeezes the conduit.

15. Control apparatus according to claim 14 in which the longitudinal support and the individual elements, in combination, form a closed channel along which the conduit extends.

16. Control apparatus according to claim 15 in which the longitudinal support is in the form of an open-sided channel, the open side being covered by the said elements.

17. Control apparatus according to claim 16 in which the individual elements are held in position by in-turned lips on the free edges of the open-sided channel.

18. Control apparatus according to claim 15, 16 or 17 in which each individual element includes a flange located outside the channel and in which the flanges of all the said elements are in alignment.

19. Control apparatus according to claim 15 in which the conduit extends in two runs along the channel and in which each individual element of the load transfer means contacts both runs.

20. Control apparatus according to any one of claims 14 to 18 in which each individual element of the force transfer means includes a rib or wall in contact with the conduit.

21. Control apparatus according to any one of claims 14 to 20 installed along one edge of a door so that pressure is applied to the force transfer means when the said edge meets an obstruction.

22. Control apparatus substantially as described with reference to Figures 1 and 3

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. have been provided to respond to pressure change arising at selected points along the tube 3, it would be possible instead to provide a means for sensing the pressure drop along the selected length of the tube, such as the portion 3c, so that the difference between the pressure at the respective ends of the selected portion is sensed. Means would also be included to produce a control signal, or operate a switch or other device, in response to variation in the sensed pressure difference. With such an arrangement, it is less important that the pressure source should provide a constant output pressure, since variation in the output pressure will, to some extent, not cause corresponding variations in the sensed pressure difference such as to cause production of the control signal etc. e WHAT WE CLAIM IS:

1. Control apparatus comprising: a conduit which can be restricted at at least one position along its length; means for causing a flow of fluid in the conduit; and a sensor which responds to a variation in the flow, caused by restriction of the conduit, to produce a signal.

of the accompanying drawings and substantially as illustrated therein.

23. Control apparatus substantially as described with reference to Figures 1 and 4 of the accompanying drawings and substantially as illustrated therein.

24. Control apparatus substantially as described with reference to Figures 5 and 3 of the accompanying drawings and substantially as illustrated therein.

25. Control apparatus substantially as described with reference to Figures 5 and 4 of the accompanying drawings and substantially as illustrated therein.

26. Control apparatus substantially as described with reference to Figures 6, 7 and 8 of the accompanying drawings.