GB2107424A - Power-operated can opener having epicyclic reduction gearing - Google Patents

Abstract

A power operated can opener has a generally cylindrical casing 1, 2, 9 assembled without fasteners, and a handle 3 extending along its midplane. The can is guided by a fixed guide 17 into engagement with a traction roll 6 and cutter roll 7, whose axes are skew to each other, and which sever the outer sidewall of the can end seam by a peeling action. The rolls are arranged in fixed positions relative to the body of the appliance, i.e. they are not moved into engagement with the can. Speed reduction between motor 45 and rolls is by single-stage pericycloidal drive 18 comprising a fixed internal ring gear 86 and a output internal ring gear 8 engaged respectively by portions 87, 88 of a stepped planet gear 10 carried by an eccentric sleeve 11 which is mounted on a motor-driven shaft 106. <IMAGE>

Description

SPECIFICATION Power-driven appliances This invention relates to power-driven appliances.

The term "appliance" is to be understood to mean a device, tool or machine for performing mechanical work in a domestic, industrial or other situation (but especially in a domestic situation). Where the context requires, the term "appliance" is further restricted by implying such a device, tool or machine capable of being, or adapted to be, carried by a person and/or held by the user's hand during operation of the appliance.

The invention is particularly, though not exclusively, applicable to power-driven can openers, and will be discussed hereinafter with reference to can openers, but without prejudice to the generality of its practical applicability to other appliances.

There have been proposed, or there have been commercially available, a number of designs for can openers driven by electric motors. Basically an electric can opener is a labour-saving tool, which is useful either where the user does not wish to exert the manual force often necessary to operate a can opener of one of the many manually-operated kinds that are available, or where he or she is not capable of exerting that force readily, or where there is a requirement for a relatively large number of cans to be opened in the course of a day. The latter situation applies especially in catering establishments, in which speed is of the essence, and where each operation carried out by the staff desirably involves the least possible movement and effort.

In power-driven can openers or other appliances known to us, where a reduction in speed of rotation is required as between the motor and the rotating tool element or elements or the like, there is provided a mechanical transmission in the form of spur or worm gearing, or a combination of both. In a can opener the speed reduction had necessarily to be extremely high, and will typically be of the order of 150:1. Using a conventionally geared transmission, a reduction ratio of this magnitude will in practice require at least two stages. This adds to the complication of the appliance, increases energy losses due to friction, backlash etc, and tends to make the appliance more noisy. Use of a multi-stage transmission also increases the cost of the appliance and provides additional components which may fail.

According to the invention, in a first aspect thereof, in a power-driven appliance, being a device, tool or machine for performing mechanical work, for exerting a high rotational output torque at low rotational velocity and having power transmission means arranged to be driven at an input velocity very substantially higher than the said low velocity and to deliver said high torque at said low velocity, the transmission means comprises pericycloidal drive means.

In this context, the expressions "high torque" and "low rotational velocity" are to be read in the light of the fact that the values of torque and rotational velocity required to open a steel can are typical though non-limiting.

A pericycloidal transmission means is a gear train comprising: a first gear in the form of an internal gear ring which may be stationary; an intermediate wheel having a second gear and a third gear, second and third gears being arranged circumferentially of the wheel about a common axis of the wheel; and a fourth gear in the form of an internal gear ring rotatable about its axis which is the same axis as that of the first gear and may be called the main axis. The axis of the intermediate wheel is parallel to the main axis but eccentric thereto by a constant radial distance. The second and third gears engage the first and fourth gears, respectively, and the diameters of the gears of the intermediate wheel differ from each other but only slightly.Similarly the difference between the number of teeth in the first gear, and that in the fourth gear, is usually only slightly greater than that in the co-operating second or third gear, respectively. The intermediate wheel is freely rotatable about an eccentric carrier which is driven rotatingly about the main axis, so causing the eccentric axis to perform a cylinder of revolution; the gears of the intermediate wheel thus roll around the first and fourth gears, the rotational velocity R1 of the intermediate wheel about its own (i.e. the eccentric) axis being determined by the rotational velocity RD of the carrier and the tooth ratio of the first and second gears. Since the latter is nearly 1:1, the velocity RI can be very small compared with RD.If the first gear is fixed, then if the second and third gears were of the same diameter, the fourth gear would not be rotated. If the overall reduction ratio is RD/Ro, where RO is the rotational velocity at the output of the gear train, i.e. the rotational velocity of the fourth gear, then under these conditions RD/Ro is infinite. In practice, because of the slight difference between the diameters of the second and third gears, a small difference exists between the velocities of the first and fourth gears. Suitable balance weights are provided to compensate for the dynamic unbalance caused by the eccentric rotation.

As described above, the pericycloidal transmission means has a single stage. It is of course possible to couple the fourth gear with the carrier of a second stage in order to achieve still greater reduction in rotational output velocity.

Use of a pericycloidal drive in a power-operated appliance, provides a means for obtaining a high reduction ratio, as between the motor and the operative, driven rotating parts ofthe appliance, which is compact, simple in construction, has few moving parts and is consequently less noisy as compared with for example a train of spur gears, and which also can be easier to assemble and less expensive and has better mechanial efficiency than the types of gears conventionally found particularly in domestic appliances such as electric can openers.

Preferably the first gear ring is stationary in a casing of the appliance.

Where the latter is a can opener, with the percycloidal drive means rotatably coupling the motor to one or more rotatable can-engaging elements of the can opener for exerting the high rotational torque on a can, the drive means is preferably in the form of a single unit providing the entire speed reduction, in a simple stage, between the motor and the canengaging element or elements.

In a preferred embodiment of such a can opener, there are two such rotatable can-engaging elements, viz. a traction roll and a cutting roll for co-operation with each other to rotate about its own axis a can held by the can opener whilst the cutter roll progressively severs the can, and the two rolls have intermeshing gear teeth so that both rolls are driven positively through the pericyicoidal drive means.

In a power-driven can opener according to the invention, the pericycloidal drive gives a reduction ratio of the order of 150:1.

In a kitchen in which a number of people are working, there is a likelihood that some people will be right-handed and others left-handed. In an operation such as the opening of a can, it is usually found that the can opener is more suitable for right-handed users than for those who are left-handed. This is particularly so in the case of most manuallyoperated can openers (whether of a portable type or of a kind fixed to a wall or to a horizontal surface), the operating handle or butterfly key being placed so as to be on the right-hand side of the can opener body when the device is held in the left hand.

According to the invention, in a second aspect thereof, has: a body defining a front and rear end of the can opener and comprising a casing and a carrying handle carried by the casing, the handle extending longitudinally of the casing and substantially bisected by a longitudinal plane; a traction roll and a cutter roll at the front end of the body, each rotatable about its own axis so that the rolls co-operate with each other to grip and support a can whilst rotating it about an axis of the can lying in the said longitudianl plane and the cutter roll progressively severs the can along a path encircling the said can axis, the can opener having in the body a motor and means rotatably coupling the motor with at least one of said rolls, and a manual control element for the can opener being substantially bisected by the said longitudinal plane and arranged for actuation by an operator's hand gripping the carrying handle, whereby the can opener is operable with one hand, being either left or right hand of the operator.

Such a hand-held can opener is suitable for use equally conveniently by users who are right-handed or left-handed. This is achieved by eliminating any separately-operable device for effecting clamping of the can to the appliance, and by arranging its can-engaging parts at the front end of the can opener body, the operative engagement of can and opener taking place in the region of a longitudinally extending vertical mid-plane of the opener, so that a left-handed user will hold the appliance to the left of the can whilst a right-handed user will hold it to the right, with equal facility. The only actuating device is a switch or the like for applying power to the appliance, and this actuating device is centred on the same mid-plane for convenient operation by the hand that is holding the can opener.

Electric can openers, are usually designed to be fixed to a vertical or horizontal surface with the cutting and other can-engaging elements of the can opener arranged either at the front (facing the user), or at either one of the sides, of the appliance. As with all manually-operated can openers, two hands are usually needed to operate a power-operated opener, viz. one hand to hold the can whilst the other hand is used for the purpose of operating a lever or other similar device to effect initial clamping of the can to the appliance, prior to commencement of the opening operation.Electric can openers have been proposed in which the motor is automatically started when the can is clamped in position, for example by operation of a micro-switch actuated by the manually operated clamping mechanism or by the mechanism which effects (under manual operation) the initial piercing of the can.

The lever or other similar device which has to be moved in order to effect clamping of the can to the can opener is, like the operating handle of a manually-operated can opener, inherently such that, if it is in its most convenient position for operation by the user's right hand, it will not be in the most convenient position for his or her left hand. Furthermore, the initial clamping operation can often increase the overall time taken for opening the can, to the disadvantage of a catering kitchen and also to the disadvantage of a purely domestic user.

In addition, the provision of a clamping mechanism in itself complicates the appliance, renders it more expensive to make and to buy, more difficult to clean, more liable to develop faults, and heavier.

According to the invention in a third aspect thereof, a power-driven can opener has: a body including a carrying handle; a traction roll and a cutter roll, each rotatable about its own axis so that the rolls-coperate with each other to grip and support a can whilst rotating it about an axis of the can and the cutter roll progressively severs the can along a path encircling a path encircling said can axis; means for rotating at least one of the said rolls about its own axis, the position and orientation of the cutter roll being constant with respect to the body and the traction roll being resiliently biassed axially inwardly for limited, automatic outward axial movement in response to initial engagement of a can with the rolls, so that the rolls cannot otherwise move relative to each other except in the sense of rotation about their respective axes; and a fixed reaction guide element on the body for engaging the top of a double end seam of a can ahead of the said rolls in the direction of rotation of the can with respect to the can opener, whereby to guide the can in its rotation about its own axis and to exert a reaction force thereon.

Simplicity of construction and ease of assembly, both during initial manufacture and after dismantling for maintenance or repair, are of course always desirable in respect of any machine. Amongst the ways in which improved simplicity of construction and ease of assembly are achieved in the can opener described hereinafter, is a form of construction of the body of the appliance from which separate fasteners, such as screws, are absent or substantially absent.In this form of construction, typified by the can opener but applicable to any portable powerdriven domestic appliance, and in accordance with the invention in a fourth aspect thereof, the ap pliance has a body which includes a substantially cylindrical main casing of the appliance, the main casing being assembled without separate fasteners and comprising at least three members in the form of a mounting member and a pair of hollow shell members secured together by the mounting plate, each member being secured to the adjacent member by means of integral, circumferentially extending interrupted projections of one member engaging corresponding circumferentially-extending interrupted recesses in the other member.This arrangement where the casing is substantially cylindrical renders unnecessary, or (at worst) optional, the bolts, self-tapping screws and other small fasteners which universally characterise the assembly of the casings of domestic appliances.

In the can opener according to the invention in at least its third aspect discussed above, elimination of a separate clamping mechanism is an advantage to gained by adoption of the particular configuration of can-engaging elements employed in preferred embodiments. There are essentially three of these elements which engage the can throughout the opening operation. These are the traction roll, the cutter roll and the fixed reaction guide element, which is typically in the form of an abutment projecting forwardly of, and which is preferably formed integrally with, the body of the appliance.As has already been explained above, the only movements of the two rolls relative to each other (or indeed relative to the can opener body) that are permitted are the rotation of each roll about its own axis and the limited outward axial movement (against resilient biassing means) of the traction roll when the latter is forced so to move by contact with the can on initial engagement. The purpose of this movement is to enable the can opener to operate on cans of different radial thicknesses of seams. It is important to note that this adjustment takes place entirely automatically, and it is this facility, combined with the arrangement of the can-engaging elements themselves, that enables separate actuating means (for clamping the can in position) to be omitted.

In a preferred arrangement of such a can opener, the cutter roll has a curved peripheral surface terminating in a circumferential cutting edge for engaging a circumferential outer wall of the double end seam of the can, the traction roll having a peripheral surface for engaging on the top of the said can seam, the peripheral surface of the traction roll being tangent to a first plane substantially containing a can-engaging surface of the reaction guide element, the cutter roll being on the opposite side of the said first plane from the traction roll, the traction roll further having a chuck wall engaging surface for engaging a chuck wall of the said seam, the axis of the traction roll defining the intersection between a second plane, parallel to said first plane, and a third plane perpendicular to said first plane, said third plane being radial with respect to the can, the axis of the cutter roll defining the inersection between a fourth plane and a fifth plane, said fourth plane being perpendicular to said third plane and divergent from said second plane outwardly from the body, a cutter incline angle in the range 10 to 300 being defined between said second and fourth planes, said fifth plane being perpendicular to said first plane and convergent towards said third plane outwardly from the the body, and a cutter offset angle greater than zero being defined between said third and fifth planes, the curved peripheral surface of the cutter roll being such that a generator thereof is inclined, in the region where the cutting edge contacts the outer wall of the seam, from the cutting edge toward said first plane, whereby when the abutment and traction roll are engaged on the top of said can seam and the cutting edge with said outer wall thereof, and a said roll is rotated to effect relative circumferential movement between the opener and the can such that the centre of the cutter roll is behind the centre of the traction roll in the direction of relative movement of the opener, the cutting edge engages the can seam outer wall at an angle thereto substantially equal to the cutter incline angle to sever the outer wall with a cutting force having a substantially minor radial component and the outer peripheral surface of the cutter roll lifts and peels radially inwardly the severed edge of the seam.This arrangement enables the can, with its top seam checked and guided by the reaction guide element, to be drawn automatically, into full rotating and cutting engagement with the respective rolls, by the traction and cutting rolls themselves, the can then being clamped between the rotating rolls in a kind of tripod support arrangement of which the reaction guide element forms the third support.

Preferably, the can opener has two fixed guide elements on the body for engaging the top of the said can seam, said elements comprising, as the first guide element, the said reaction guide element ahead of the rolls, and as the second guide element a projection which is behind the said rolls in the direction of rotation of the can with respect to the can opener whereby to guide the can into initial engagement with the traction roll and cutter roll.

It will be appreciated that an appliance the subject of this Application may be electrically-powered, or driven by a fluid such as compressed air or another compressed gas such as carbon dioxide, the motor and its actuating switch or equivalent device being chosen accordingly.

An embodiment of the invention, in the form of a power-driven can opener, will now be described, by way of example only, with reference to the drawings hereof, in which: Figure lisa side elevation of the power-driven can opener, seen mainly in section upon the longitudinal vertical centre plane (indicated at P2 in Figure 2) of the can opener; Figure 2 is a front elevation partly in section on the line ll-ll in Figure 1 of the same can opener; Figure 3 is a perspective view, partly broken away, of the same can opener, shown with a partly-opened metal can engaged therewith; Figure 4 is a diagrammatic view of a traction roll of the can opener and a cutting edge of a cutter roll of the opener, looking from the back, that is to say from the right in Figure 1, during an operation of opening a can;; Figure 5 is a diagrammatic view of the two said rolls during a can opening operation, looking from the left-hand side of Figure 4; and Figure 6 is a diagrammatic plan view showing the cutter roll during a can opening operation.

Referring first to Figures 1 to 3, the can opener shown therein is electrically powered. It has a body defining a front or can-engaging end (the left-hand end in Figure 1) and a rear end of the opener. The body comprises a casing 1, 2, 9, and a carrying handle 3 carried by the casing, the handle 3 extending longitudinally of the casing and being substantially bisected by the longitudinal vertical centre plane P2 as seen in Figure 2.

At the front end of the body there are provided can-engaging elements in the form of a traction roll 6 and a cutter roll 7, each rotatable about its own axis so that the roll 6 and the roll 7 co-operate with each other to grip and support a can 75 (Figure 3) whilst rotating the can about the central axis (indicated at Ac in Figure 6) of the can whilst exerting upon the can a high rotational output or working torque at a low rotational velocity of the rolls 6 and 7. The can axis Ac lies in the longitudinal plane P2 of the can opener whilst the can is fully engaged by the traction roll 6 and cutter roll 7.As the rolls 6 and 7 cause the can to rotate about its axis, the cutter roll 7 progressively severs the can along a path encircling the can axis, viz. along a peripheral line around the outer wall 149 of the double end seam 141 by which the can end member 143, is secured to the cylindrical body 145 of the can. The resulting circumferential cut, which when completed separates the main part of the can end 143 from the remainder of the can and enables the former to be lifted off the latter, is indicated in Figure 3 at 82.

A reversible electric motor 45 of any suitable kind is mounted within the body of the can opener and is supplied with power from a mains lead 74 through a conventional electrical circuit. The circuit includes a manual control element for the can opener, in the form of a switch 49 for energising, de-energising and reversing the motor, and internal electrical leads 83.

The motor 45 has a motor shaft 84 which is rotatably coupled, through transmission means in the form of a pericycloidal drive means generally indicated at 18, with the traction roll 6. The pericycloidal drive means 18 effects a reduction ratio, as between the speed of rotation of the motor shaft 84 and that of the traction roll 6, of 150:1. This speed reduction is achieved in a single stage by the drive means 18. In this example the motor is one capable of delivering up to one-sixth of a horsepower (0.124 kW) at 20,000 rev/min.

The construction and operation of the can opener will now be described in greater detail, with con tinued reference to Figures 1 to 3.

The main casing of the can opener is generally cylindrical in form and consists of a first shell member in the form of a hollow nose piece 1; a second shell member in the form of a hollow motor housing 2, and a generally-circular mounting plate 9, the latter being arranged between the nose piece 1 and motor housing 2, which are secured together by the mounting plate. The casing is assembled without the aid of separate fasteners such as screws, bolts etc. Instead, the two sides of the mounting plate 9 are provided circumferentially with integral interrupted screw threads which engage with corresponding circumferentially-extending interrupted threads formed integrally at the open ends of the nose piece 1 and motor housing 2. The location of these interrupted threads, by which the casing is assembled, is indicated in Figure 1 by the reference numerals 68.The motor housing 2 extends to the rear end of the can opener. The nose piece 1 has a forwardly-converging leading portion terminating in a front aperture defined by an integral, axiallyextending, tubular housing portion 67 of the nose piece. In the housing portion 67 there is mounted a cartridge 4 in the form of a cartridge body 85 which carries the traction roll 6 and cutting roll 7, as will more fully be described hereinafter.

The nose portion 1 also has an integral foot 77, Figures 2 and 3, on which the can opener rests when laid on a flat suface; and a further can-engaging member in the form of a forwardly-projecting can rest abutment 81. The abutment 81, as seen in Figure 2, has an arcuate form. It serves to steady the side wall of the can body whilst the can is being rotated during the opening operation The mounting plate 9 comprises a disc-like web having a coaxial boss, in which there is mounted a rear crankshaft bearing 22 and peripheral annular portions in which the interrupted threads 68 are formed. The annular portion that is nearer the front of the can opener is of extended length and carries on its inner face an integral, radially-inwardly facing first gear ring 86 of the pericycloidal drive means 18 (which latter will be described more fully below).A radially-outwardly extending ring portion 90 of the mounting plate 9 has opposed radial faces against which the terminal faces of the nose piece 1 and motor housing 2 lie in close abutment as seen in Figure 1. The outer circumferential surface of the ring portion 90, being thus flush with the casing components 1 and 2 and therefore being part of the outer surface of the casing, can conveniently be provided with the vents that are necessary to admit air to the rear chamber of the can opener body (i.e. to the interior of the motor housing) for the purpose of cooling the motor 45 in operation.In this example these vents are in the form of circumferentiallyextending, equally-spaced slots 73, which communicate with the interior of the motor chamber through longitudinal holes 91 (Figure 1) extending through the rearward one of the two annular portions, abovementioned, of the mounting plate.

The body of the can opener consists of its casing 1, 2, 9 together with the carrying handle 3. The handle 3 comprises a single unit in the form of a hand-grip portion 60, joined to a base plate portion 59 by a switch housing portion 61 at the front end and a cable entry housing portion 47 at the rear, and having a downwardly-depending rear plate potion 63 extending as a continuation of the rear wall of the portion 47. The actuating switch 49 is mounted in the top of the front portion 61 so as to be bisected by the longitudinal centre plane P2 as seen in Figure 2.

Since both the hand grip portion 60 and the switch 49 are on the plane P2, as are the axis of the traction roll 6 and the axis Ac of the can 75 whilst the latter is being opened, it will be understood that the can opener is equally suitable for operation by a lefthanded or a right-handed user. As will be seen hereinafter, the switch 49 constitutes the only element requiring actuation by the user's hand.

The mains cable 74 extends into the can opener body through an aperture in the rear wali of the handle rear portion 47, this aperture being centred on the longitudinal plane P2, and is clamped conventionally within the portion 47, the various wires 83 being trapped between the handle base plate portion 59 and the top of the main casing 1,2,9, and the motor housing 2 having an aperture in its top through which the appropriate wires 83 are led into the motor chamber within it.The handle3 is located upon the main casing by means of a lug 50 at its front end engaging under a lip 66 formed integrally in the top of the nose piece 1; by downwardlydepending tenons 102 engaging in grooves 103 formed on the nose piece 1 and the motor housing 2; and, at the rear end of the can opener, by a hole in the rear plate portion 63 in which there engages a rearwardly extending projection 51 of the back wall of the motor housing 2.

Since the ventilation slots 73 are of equal size and equally spaced, and since the coaxial boss of the mounting plate 9, carrying the rear crankshaft bearing 22, is coaxial, it will be appreciated that the orientation of the mounting plate about its axis, during assembly of the casing, is immaterial. This facilitiates the assembly operation. It may, however, in some embodiments be preferred to continue the tenon grooves 103 across the mounting plate 9 in which case there is only one correct orientation for the latter.

The handle 3 is in this example secured to the main casing by means of a single recessed screw 64 at the back anchoring the rear plate portion 63 to the motor housing 2. A blanking plug 54 masks the head of the screw 64. Any other suitable form of fastener may be employed in place of the screw 64. Furthermore, in another embodiment the cable 74, instead of entering the can opener body above the main casing, may enter it through the rear wall of the motor housing 2 and the rear plate portion 63 of the handle, in which case the cable may be clamped to the can opener body by means of an externallyreleasable cable clamping means of any suitable known kind. In such an arrangement this cable device also serves to secure the carrying handle to the casing; separate fastening means (such as the screw 64) would then be entirely absent from the whole body assembly.

As seen in Figure 1 and identified by the reference numeral 72, the rear wall of the motor housing 2 has a through aperture communicating with the atmosphere below the rear plate portion 63 of the handle, thus providing a rear vent. The vent 72, together with the vents 73 in the mounting plate 9 described above, provide a path through the motor chamber for continuous flow of cooling air, induced by a fan 71 which is mounted on the motor shaft 84 behind the motor 45.

The nose piece 1, motor housing 2, and mounting plate 9 are in this example of injection-moulded plastics materials. Preferably, the handle 3 and the cartridge 4 are also of injection-moulded plastics materials. Although the nose piece 1 and motor housing 2 are, as described herein before, generally cylindrical, they may be for convenience of maufacture very slightly tapered as shown, having their major diameter at the respective ends thereof abutting the ring portion 90 of the mounting plate. The tapered form of these components 1,2 may conveniently be achieved by adopting the form in which the inside surface of the shell of each component is in the form of a series of cylindrical portions joined by a multiplicity of very shallow steps (which, for the sake of simplicity, are not shown in the drawings).

The motor 45 has a frame 69 which is secured by means of a force fit within the motor housing 2. If the abovementioned steps are provided, the frame 69 can conveniently be located axially be engagement of the two flanges of the frame, indicated at 92 in Figure 1, against two respective ones of the said steps.

It will be appreciated that, in place of the interrupted thread arrangement 68 for securing together the casing members 1,2 and 9, there may be provided any other suitable securing means in the form of integral, interrupted, circumferentialiyextending projections in one member co-operating with corresponding recesses in the member secured thereto, for example a bayonet-type arrangement.

The motor or main shaft 84 rotates in bearings 70 carried by the motor frame 69, and extends forwardly beyond the latter. Immediately in front of the forward motor frame bearing 70, the shaft 84 terminates in a splined spigot 84a coaxially engaged in a splined rear end of a crankshaft 16. The latter incorporates a balance weight 13 whose purpose will become evident hereinafter. The internallysplined rear end of the crankshaft 106 is rotatable in the rear crankshaft bearing 22 already mentioned. Its other end is supported in a front crankshaft bearing 21, which is supported coaxially in the hub of an annular driving gear 8, the gear 8 being rotatable in an outer bearing sleeve 25 of low-friction material which is provided in the bore of the nose piece 1.

The crankshaft carries a cylindrical eccentric carrier sleeve 11 and a further balance weight 12. The axis of the sleeve 11 is eccentric, but parallel, to the main axis of the can opener, i.e. the axis of the crankshaft 106 upon which the sleeve 11 is secured.

The sleeve 11 carries a coaxial needle bearing 20, which supports an intermediate gear wheel, in the form of a double pinion 10, for rotation about the sleeve 11. The pinion 10 has a second gear 87 and a third gear 88 of the pericycloidal transmission, meshing respectively with the stationary first gear 86 and the annular driving gear 8 (which constitutes a fourth gear of the pericycloidal drive means).

The driving gear is thus rotatably supported in a bearing whose outer race (maintaining the gear 8 and crankshaft 106 coaxial with each other and with the main axis) is the bearing sleeve 25. The eccentric sleeve 11 serves as an inner "race" for this bearing, since at any time it is rotatably supporting the driving gear 8 internally, via the needle bearing 20 and pinion 10, at some position around its circumference.

In this example, the tooth ratios of the four gears are as follows: 1stgear86: 27 teeth 2nd gear 87: 24teeth 3rd gear 88: 23 teeth 4th gear 8: 26teeth The pericycloidal drive means comprises the stationary gear ring 86, the eccentric pinion 10 with its gears 87 and 88, the crankshaft 106 with the eccentric sleeve 11, driving gear 8, and bearings 20, 21,22,25. It will be noted that the gear 8, called the driving gear because it drives the traction and cutter rolls 6 and 7, is also the output or driven wheel of the pericycloidal drive means, and that it is capable of limited axial movement with respect to bearing sleeve 25 and pinion 10.

Rotation of the crankshaft 106 by the shaft 84 causes the driving gear 8 to rotate at about one one-hundred and fiftieth of the motor speed. This speed reduction is, as can be seen, achieved by the pericycloidal drives means in a single stage. The balance weights 12 and 13, rotating with the eccentric sleeve 11, prevent vibration due to the eccentric rotation.

The gear ring 86, the gear teeth of driving gear 8, and the pinion 10 are preferably of a synthetic plastics material such as nylon. The gear teeth themselves may be formed on separate toothed sleeves fitted to the appropriate body, viz. the body of the gear 8, the mounting plate 9 and pinion 10.

Alternatively they may be formed integrally with these bodies (as shown) provided the latter are of a material suitable for use in gearing.

The driving gear 8 has a coaxial, forwardlyextending bush 15, which is secured to the spindle 5 of the traction wheel 6 by means of a cotter pin 30, the traction wheel spindle 5 having its axis co-linear with the axis of the main shaft 84.

The cartridge body 4 is secure in the housing portion 67 of the nose piece. The driving gear bush 15 is spaced from the rear face of the body 4 by a thrust bearing 23 and a set of disc springs (Belleville washers) 26, so that the cartridge gear 8 and traction roll 6 are continuously biassed inwardly so that the back of the traction roll bears against the cartridge body 4. The gear 8 and traction roll 6 can however be moved axially outwardly (i.e. to the left as seen in Figure 1) by a limited amount against the action of the disc springs 26 upon initial engagement of a can seam 141 with the traction and cutter rolls. As will be seen, the rolls automatically assume their operative engagement with the can seam, during which the outward movement of the traction roll automatically adjusts for the can seam thickness.The springs 26 then supply the necessary axial cutting force for a can opening operation.

The cutter wheel 7 has a coaxial spindle which is freely rotatable in a bore formed in the cartridge body 4, and is positively rotated by the traction roll 6.

For this purpose the traction roll 6 and cutter roll 7 are provided with intermeshing gear teeth 76, which are shown exaggerated in Figure 2 and seen clearly in Figure 5. In Figure 1, for the sake of clarity, the cutter wheel axis is shown as though it were in the same vertical plane as the traction wheel axis.

It will be seen that (apart from the limited axial movement of the traction roll as explained above) the rolls 6 and 7 cannot move relative to each other except in the sense of rotation about their respective axes.

Formed integrally with the casing nose piece 1, projecting forwardy of the body of the can opener and extending across the front of the nose piece 1 and also across the front of the cartridge body 4, is a fixed guide fin 16, 17. This fin comprises a pair of fixed guide elements, viz. a first guide element in the form of a recaction guide 16 and a second guide element in the form of an engagement guide 17. The engagement guide 17 is inclined downwardlyto- wards the axis of the can opener by a small acute angle as shown in Figure 2, whereas the lower or can-engaging surface 16A of the reaction guide 16 is horizontal, i.e. perpendicular to the plane P2.

The direction of rotation of the can 75 during the opening operation is indicated by the arrow in Figure 3, and it will be noticed that the engagement guide 17, whose lower surface engages the top of the can seam 141 during intitial engagement of the can with the can opener, is therefore behind the reaction guide 16, considered in the direction of rotation of the can. The purpose of the reaction guide, on the other hand, is to engage the top of the double end seam 141 during the opening operation, whereby to guide the can in its rotation about the can axis Ac (Figure 6) and to exert thereon the necessary reaction force to maintain the top of the can seam in a constant plane and so prevent the can from tilting sideways.

On the front guide fin, between the guide elements 16 and 17, a small downward projection 95 is provided. This may bear upon the top surface of the can end 143 during the opening operation, and assist the initial engagement of the can with the can opener.

it will have been observed from the foregoing that during the operation of opening the can 75, that is to say severing the can end 143 so that it may be lifted off the remainder of the can, the can is essentially engaged by four can-engaging elements, viz. the traction roll 6, cutter roll 7, reaction guide 16 and (preferably) the can side support abutment 81. The interaction of the elements 6,7 and 16 will now be briefly described, with reference to Figures 4 to 6.

Figures 4 and 5 illustrate the circumferential cutting edge 96 of the cutter roll 7 forming the cut 82 in the outer wall 149 of the double end seam 141 of the can. During cutting, the depth of the cut is limited by a flat abutment 105, called a depth limiter, on the front face of the cutter 7. This prevents more than one thickness of the metal of the can end seam from being severed. The direction of movement of the part of the can being cut, with respect to the can opener, is indicated by the straight arrow in Figure 4.

The cutter roll has a curved (viz. cylindrical) peripheral surface 97 terminating in the cutting edge 96, whilst the traction roll 6 has peripheral surface in the form of a cylindrical surface 98 for engaging and rolling upon the top of the can seam. The traction roll surface 98 is tangent to a first plane Ps. The plane P5 is horizontal and contains the top of that part of the can seam that is not yet severed. Subject only to the very slight gap between the plane P5 and the top of that part of the can seam that has been severed (see the left-hand side of Figure 4), the plane P5 can be said also to contain the can-engaging surface 16A of the reaction guide abutment 16. As can also be seen from Figure 4, the traction roll 6 and cutter roll 7 lie on opposite sides of the plane P5.The traction roll also has a chuck wall engaging surface 99 for engaging the chuck wall 100 of the can end seam 141, and the axis OT of the traction roll 6 defines the intersection between a second plane P3 (Figure 5) and the plane P2, which is the longitudinal midplane of the can opener and which contains the can axis Ac. Planes P3 and P5 are perpendicular to each other.

The cutter roll axis 0c defines, similarly, the intersection between a fourth plane P4 and a fifth plane P6.

Plane P4 iS perpendicular to plane P2 and is also divergent from the plane P3 outwardly from the front end of the can opener body.

Between planes P3 and P4 there is defined a cutter incline angle p whose value is 15 in this example, though it may have any value in the range 10" to 300.

Plane P6 is perpendicular to plane P5, and is convergent towards the midplane P2, outwardly from the front end of the can opener body. Between planes P2 and Pe there is defined a cutter offset angle y whose value is greater than zero and not greater than 10 . In this example the cutter offset angle is 6 .

The surface 97 of the cutter roll is such that a generator 101, Figure 6, thereof is upwardly inclined, at least in the region where the cutter roll 7 contacts the outer can seam wall 149 as indicated atA in Figure 4, from the cutting edge 96 towards the plane P5.

Finally, the axis Oc of the cutter roll 7 is in advance of the axis OT of the traction roll 6 in the region where they engage the can, considered in the direction of movement of the can relative to the can opener (i.e. behind the axis OT in the direction of movement of the opener relative to the can). In Figure 4 there is shown a sixth plane P1, containing the axis of the traction roll and also the centre of the cutter roll in the plane of the cutting edge 96. The planes P1 and P2 contain a trail angle whose value is approximately 16".

It will be seen from the foregoing that the axes of the traction and cutter rolls are in a skew relationship to each other. By virtue of the arrangements described, the positioning of the cutter roll 7 relative to the frusto-conical surface 99 of the traction roll 6 is such that the cutting edge 96 cuts into the can seam outer wall in advance of the plane P1, viz. in the region B indicated in Figure 4. This is thus ahead of the narrowest region between the two rolls 6, 7. The narrowing of the gap between the two rolls then causes the upper portion of the cut seam wall to be crimped.The slope provided by the generator 101 (Figure 6) of the cutter roll surface 97 in the direction of the cutter roll axis, relative to the plane P5 containing initially the top of the can seam, causes the upper portion of the can seam outer wall to be curled inwardly during crimping, so concealing any jagged edge produced by the cutting operation. In addition, the curled edge is lifted as it passes over the top of the cutter roll 7.

In order to commence a can opening operation, the surface 99 of the traction roll 6 is guided down into engagement with the chuck wall of the can end seam by the engagement guide 17, and a point such as Con the cutting edge 96 of the cutter roll is ressed into contact with the outer seam wall 149. The switch 49 is now operated to energise the motor of the can opener and so rotate the traction roll and cutter roll, their directions of rotation being indicated in Figure 4. The frusto-conicai surface 99 is ribded and the cutting edge 96 is serrated. The surface 99 and edges 96 frictionally engage the chuck wall 100 and outer seam wall 149 respectively. This, coupled with the skew arrangement of the two rolls already mentioned, ensures that rotation of the traction roll 6 as for forward movement of the can opener causes the centre of the cutter roll to rotate about the point C. As a result, the centre of the cutter roll 7 moves downwardly away from the can end, forcing the traction roll 6 downwardly until its peripheral surface 98 engages the top of the can end seam, and the cutting edge 96 bites into the outer seam wall until the depth limiter 105 prevents further penetration radially. At the same time the top of the can seam is brought into contact with a suitable point on the can engaging surface 6A of the reaction guide, whilst the side wall of the can is steadied by the abutment 81 (Figure 1).

Continued rotation of the rolls 6 and 7, with the cutting edge 96 engaging the can seam outer wall 149 at an angle thereto substantially equal to the cutter incline angle p, causes the cutter roll to sever the wall 149, whilst the cutter surface 97 lifts and peels the severed edge of the seam radially inwardly.

Claims (16)

1. A power-driven appliance (as herein before defined) for exerting a high rotational output torque at low rotational velocity and having power transmission means arranged to be driven at an input velocity very substantially higher than the said low velocity and to deliver said high torque at said low velocity, wherein the transmission means comprises pericycloidal drive means.

2. A power-driven appliance according to Claim 1, the pericycloidal drive means comprising: a generally-cylindrical carrier having an intermediate gear wheel freely rotatable coaxially thereon, the carrier being arranged to be rotatably driven at said input velocity in rotation about a main axis of the drive means and the axis of the intermediate gear wheel being eccentric and parallel to the main axis; an inwardly facing first gear ring, the intermediate gear wheel having a second gear of slightly smaller diameter than, and in engagement with, the first gear ring, and a third gear of slightly different diameter than the second gear; and a driven wheel having a coaxial inwardly facing fourth gear ring of slightly larger diameter than, and in engagement with, the third gear, the first and fourth gear rings being coaxial on the main axis, wherein the first gear ring is stationary in a casing of the appliance.

3. A power-driven appliance according to Claim 1 or Claim 2, being a can opener having a motor and at least one rotatable can-engaging element for exerting said high rotational output torque on a can, wherein the pericycloidal drive means rotatably couples the motor to said can-engaging element or at least one of said elements.

4. A power-driven can-opener according to Claim 3, wherein the pericycloidal drive means comprises a single unit providing the entire speed reduction between the motor and the said canengaging element or elements.

5. A power-driven can opener according to Claim 3 or Claim 4, having two said rotatable can-engaging elements, viz. a traction roll and a cutter roll for co-operation with each other to rotate about its own axis a can held by the can opener whilst the cutter roll progressively severs the can, said pericycloidal drive means rotatably coupling the motor to at least one of the traction roll and cutter roll.

6. A power-driven can opener according to Claim 5 when dependent on Claim 2, wherein the pericycloidal drive means is coupled with the traction roll so as to drive the traction roll, the traction roll axis and said main axis being coincident.

7. A power-driven can opener according to Claim 5 or Claim 6, wherein the traction roll and the cutter roll are provided with intermeshing gear teeth whereby the roll driven by the motor through the pericycloidal drive means drives the other roll in positive rotation.

8. A power-driven appliance according to any one of the preceding claims, wherein at least the gears of the pericycloidal drive means are of synthetic plastics material.

9. A power-driven can opener according to any one of Claims 5 to 7, having: a body defining a front and rear end of the can opener and comprising a casing and a carrying handle carried by the casing, the handle extending longitudinally of the casing and substantially bisected by a longitudinal plane; a traction roll and a cutter roll being atthefront end of the body, the motor and pericycloidal drive means being within the body, and a manual control element for the can opener being substantially bisected by the said longitudinal plane and arranged for actuation by an operator's hand gripping the carrying handle, whereby the can opener is operable with one hand, being with equal facility either the left or right hand of the operator.

10. A power-driven can opener according to any one of Claims 5 to 7 or Claim 9, wherein the position and orientation of the cutter roll is constant with respect to the body and the traction roll being resiliently biassed axially inwardly for limited, automatic outward axial movement in response to initial engagement of a can with the rolls, so that the rolls cannot otherwise move relative to each other except in the sense of rotation about their respective axes, the can opener having a fixed reaction guide abutment projecting from the front end of the body to engage on the top of the double end seam of a can ahead of the said rolls in the direction of rotation of the can with respect to the can opener, whereby to guide the can in its rotation about its own axis and to exert a reaction force thereon.

11. A portable, power-driven domestic appliance, being an appliance according to any one of the preceding claims, having a body which includes substantially cylindrical main casing of the appliance, the main casing being assembled without separate fasteners and comprising at least three members in the form of a mounting member and a pair of hollow shell members secured together by the mounting plate, each member being secured to the adjacent member by means of integral, circumferentially-extending interrupted projections of one member engaging corresponding circumferentiallyextending interrupted recesses in the other member.

12. A power-driven can opener having: a body defining a front and rear end of the can opener and comprising a casing and a carrying handle carried by the casing, the handle extending longitudinally of the casing and substantially bisected by a longitudinal plane; a traction roll and a cutter roll at the front end of the body, each rotatable about its own axis so that the rolls co-operate with each other to grip and support a can whilst rotating it about an axis of the can lying in the said longitudinal plane and the cutter roll progressively severs the can along a path encircling the said can axis, the can opener having in the body a motor and means rotatably coupling the motor with at last one of said rolls, and a manual control elementforthe can opener being substantially bisected by the said longitudinal plane and arranged for actuation by an operator's hand gripping the carrying handle, whereby the can opener is operable with one hand, being either the left or right hand of the operator.

A power-driven can opener according to Claim 12, wherein the motor is an electric motor connected with a power supply cable extending generally longitudinally through the rear end of the can opener in a cable entry substantially bisected by the said longitudinal plane, the manual control element being an operating switch for the motor.

14. A power-driven can opener according to Claim 13, wherein the cable entry comprises a cable clamping device securing the carrying handle to the casing.

15. A power-driven can opener according to any one of Claims 12 to 14, having an abutment projecting from the front end of the body to engage on the top of the double end seam of a can, the cutter roll having a curved peripheral surface terminating in a circumferential cutting edge for engaging a circumferential outer wall of the said can seam, the traction roll having a peripheral surface for engaging on the top of the said can seam, the said peripheral surface of the traction roll being tangent to a first plane substantially containing a can-engaging surface on the abutment, the cutter roll being on the opposite side of the said first plane from the traction roll, the traction roll further having a chuck wall engaging surface for engaging a chuck wall of the said can seam, the axis of the traction roll defining the intersection between a second plane, parallel to said first plane, and a third plane, being the said longitudinal plane containing the axis of the can, said third plane being perpendicular to the first plane, the axis of the cutter roll defining the intersection between a fourth plane and a fifth plane, said fourth plane being perpendicular to said third plane and divergent from said second plane outwardly from the front end of the body, a cutter incline angle in the range of 100 to 30 being defined between said second and fourth planes, said fifth plane being perpendicular to said first plane and convergent towards said third plane outwardly from the front end of the body, and a cutter offset angle greater than zero being defined between said third and fifth planes, the curved peripheral surface of the cutter roll being such that a generator thereof is inclined, in the region where the cutting edge contacts the outer wall of the seam, from the cutting edge toward said first plane, whereby when the abutment and traction roll are engaged on the top of the said can seam and the cutting edge with said outer wall thereof, and a said roll is rotated to effect relative circumferential movement between the opener and the can such that the centre of the cutter roll is behind the centre of the traction roll in the direction of relative movement of the can opener, the cutting edge engages the can seam outer wall at an angle thereto substantially equal to the cutter incline angle, to sever the outer wall, and the outer peripheral surface of the cutter roll lifts and peels radially inwardly the severed edge of the seam.

16. A power-driven can opener constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the drawings hereof.

16. A power-driven can opener according to any one of Claims 12 to 15, wherein the motor is coupled with the traction roll so as to drive the traction roll.

17. A power-driven can opener according to any one of Claims 12 to 16, wherein the traction roll and the cutter roll are provided with intermeshing gear teeth whereby the roll driven by the motor drives the other roll in positive rotation.

18. A power-driven can opener having: a body including a carrying handle; a traction roll and a cutter roll, each rotatable about its own axis so that the rolls co-operate with each other to grip and support a can whilst rotating it about an axis of the can and the cutter roll progressively severs the can along a path encircling said can axis; means for rotating at least one of the said rolls about its own axis, the position and orientation of the cutter roll being constant with respect to the body biassed axially and the traction roll being resiliently biassed inwardly for limited, automatic outward axial movement in response to initial engagement of a can with the rolls, so that the rolls cannot otherwise move relative to each other except in the sense of rotation about their respective axes; and a fixed reaction guide element on the body for engaging the top of a double end seam of a can ahead of the said rolls in the direction of rotation of the can with respect to the can opener, whereby to guide the can in its rotation about its own axis and to exert a reaction force thereon.

19. A power-driven can opener according to Claim 18, having two fixed guide elements on the body for engaging the top of the said can seam, said elements comprising, as the first guide element, the said reaction guide element ahead of the rolls, and as the second guide element a projection which is behind the said rolls in the direction of rotation of the can with respect to the can opener whereby to guide the can into initial engagement with the traction roll and cutter roll.

20. A power-driven can opener according to Claim 18 or Claim 19, wherein the body defines a front end and a rear end of the can opener, the traction roll, cutter roll and said fixed guide element or elements being situated at the front end with the guide element or elements projecting forwardly of the body.

21. A power-driven can opener according to any one of Claims 18 to 20, wherein the said guide element, or at least one of said fixed guide elements as the case may be, is in the form of a fin.

22. A power-drien can opener according to Claim 19, or Claim 20 when dependent on Claim 19, wherein the fixed guide elements are in the form of fins having respective surfaces for engaging the top of a double end seam of a can, the said can-engaging surfaces being in planes defining a shallow acute angle between them.

23. A power-driven can opener according to any one of Claims 18 to 22, wherein the cutter roll has a curved peripheral surface terminating in a circumferential cutting edge for engaging a circumferential outer wall of the double end seam of the can, the traction roll having a peripheral surface for engaging on the top of the said can seam, the peripheral surface of the traction roll being tangent to a first plane substantially containing a can-engaging surface of the reaction guide element, the cutter roll being on the opposite side of the said first plane from the traction roll, the traction roll further having a chuck wall engaging surface for engaging a chuck wall of the said seam, the axis of the traction roll defining the intersection between a second plane, parallel to said first plane, and a third plane perpen dicularto said first plane, said third plane being radial with respect to the can, the axis of the cutter roll defining the intersection between a fourth plane and a fifth plane, said fourth plane being perpendicular to said third plane and divergent from said second plane outwardly from the body, a cutter incline angle in the range 100 to 300 being defined between said second and fourth planes, said fifth plane being perpendiular to said first plane and convergent towards said third plane outwardly from the body, and a cutter offset angle greater than zero being defined between said third and fifth planes, the curved peripheral surface of the cutter roll being such that a generator thereof is inclined, in the region where the cutting edge contacts the outer wall of the seam, from the cutting edge toward said first plane, whereby when the abutment and traction roll are engaged on the top of said can seam and the cutting edge with said outer wall thereof, and a said roll is rotated to effect relative circumferential movement between the opener and the can such that the centre of the cutter roll is behind the centre of the traction roll in the direction of relative movement of the opener, the cutting edge engages the can seam outer wall at an angle thereto substantially equal to the cutter incline angle to sever the outer wall with a cutting force having a substantially minor radial component and the outer peripheral surface of the cutter roll lifts and peels radially inwardly the severed edge of the seam.

24. A portable, power-driven domestic appliance having a body which includes a substantially cylindrical main casing of the appliance, the main casing being assembled without separate fasteners and comprising at least three members in the form of a mounting member and a pair of hollowshell members secured together by the mounting plate, each member being secured to the adjacent member by means of integral, circumferentially-extending interrupted projections of one member engaging corresponding circumferentially-extending interrupted recesses in the other member.

25. A portable, power-driven domestic appliance according to Claim 24, in the form of a can opener whose body includes a said main casing consisting of a first said shell member carrying can-engaging elements at a front end of the can opener, a second said shell member extending to and defining a rear end of the can opener, and a said mounting member secured to and between the first and second shell members, the body further including a carrying handle extending longitudinally of the main casing and attached to at least one of the casing members.

26. A portable, power-driven domestic appliance according to Claim 24 or Claim 25, wherein the casing members are of injection-moulded synthetic plastics.

27. A portable, power-driven can opener according to Claim 25, wherein the casing members and the carrying handle are of injection-molded synthetic plastics.

28. A portable, power-driven domestic appliance according to any one of Claims 24 to 27, wherein the circumferentially-extending interrupted projections integral with each casing member are in the form of helical screw threads.

29. A power-driven can opener constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the drawings hereof.

New claims or amendments to claims filed on 11 January 1983 Superseded claims 1-29 New or amended claims:

1. A power-driven can opener having a motor, a traction roll, and a cutter roll for cooperation with the traction roll to rotate about its own axis a can held by the can opener whilst the cutter roll progressively severs the can, at least one of said rolls being coupled to the motor through pericycloidal drive means comprising: a generally-cylindrical carrier having an intermediate gear wheel freely rotatable coaxially thereon, the carrier being arranged to be rotatably driven at said input velocity in rotation about a main axis of the drive means and the axis of the intermediate gear wheel being eccentric and parallel to the main axis; an inwardly facing first gear ring, the intermediate gear wheel having a second gear of slightly smaller diameter than, and in engagement with, the first gear ring, and a third gear of slightly different diameter than the second gear; and a driven wheel having a coaxial inwardly facing fourth gear ring of a slightly larger diameter than, and in engagement with, the third gear, the first and fourth gear rings being coaxial on the main axis, wherein the first gear ring is stationary in a casing of the appliance.

2. A power-driven can opener according to Claim 1, wherein the traction roll and the cutter roll are provided with intermeshing gear teeth whereby the roll driven by the motor through the pericycloidal drive means drives the other roll in positive rotation.

3. A power-driven can opener according to Claim 1 or Claim 2, having: a body defining a front and rear end of the can opener and comprising a casing and a carrying handle carried by the casing, the handle extending longitudinally of the casing and substantially bisected by a longitudinal plane; a traction roll and a cutter roll being at the front end of the body, the motor and pericycloidal drive means being within the body, and a manual control element for the can opener being substantially bisected by the said longitudinal plane and arranged for actuation by an operator's hand gripping the carrying handle, whereby the can opener is operable with one hand, being with equal facility either the left or right hand of the operator.

4. A power-driven can opener according to any one of Claims 1 to 3, wherein the position and orientation of the cutter roll is constant with respect to the body and the traction roll is resiliently biassed axially inwardly for limited, automatic outward axial movement in response to initial engagement iof a can with the rolls, so that the rolls cannot otherwise move relative to each other except in the sense of rotation about their respectie axes, the can opener having a fixed reaction guide abutment projecting from the front end of the body to engage on the top of the double end seam of a can ahead of the said rolls in the direction of rotation of the can with respect to the can opener, whereby to guide the can in its rotation about its own axis and to exert a reaction force thereon.

5. A portable, power-driven can opener according to any one of the preceding claims, having a body which includes a substantially cylindrical main casing of the appliance, the main casing being assembled without separate fasteners and comprising at least three members in the form of a mounting member and a pair of hollow shell members secured together by the mounting plate, each member being secured to the adjacent member by means of integral, circumferentially-extending interrupted projections of one member engaging corresponding circu mferentially-extending interrupted recesses in the other member.

6. A power-driven can opener having: a body defining a front and rear end of the can opener and comprising a casing and a carrying handle carried by the casing, the handle extending longitudinally of the casing and substantially bisected by a longitudinal plane; a traction roll and a cutter roll at the front end of the body, each rotatable about its own axis so that the rolls cooperate with each other to effect initial gripping engagement with a circumferential end seam of a can, and thereafter to grip and support the can by said end seam whilst roating the can about an axis of the can lying in the said longitudinal plane, the cutter roll progressively severing the can along a radially outwardy facing portion of the end seam, whilst the traction roll is driven rollably along an upwardly facing surface of the end seam, the can opener having in the body a motor and means rotatably coupling the motor with at least one of said rolls, and a manual control elementforthe can opener being substantially bisected by the said longitudinal plane and arranged for actuation by an operator's hand gripping the carrying handle, and separate actuable means for effecting said initial gripping engagement being absent, whereby the can opener is operable with one hand, being either the left or right hand of the operator.

7. A power-driven can opener according to Claim 6, having an abutment projecting from the front end of the body to engage on the top of the double end seam of a can, the cutter roll having a curved peripheral suface terminating in a circumferential cutting edge for engaging a circumferential outer wall of the said can seam, the traction roll having a peripheral surface for engaging on the top of the said can seam, the said peripheral surface of the traction roll being tangent to a first plane substantially containing a can-engaging surface of the abutment, the cutter roll being on the opposite side of the said first plane from the traction roll, the traction roll further having a chuck wall engaging surface for engaging a chuck wall of the said can seam, the axis of the traction roll defining the intersection between a second plane, parallel to said first plane, and a third plane, being the said longitudinal plane containing the axis of the can, said third plane being perpendicular to the first plane, ther axis of the cutter roll defining the intersection between a fourth plane and a fifth plane, said fourth plane being perpendiculay to said third plane and divergent from said second plane outwardly from the front end of the body, a cutter incline angle in the range of 10 to 30 being defined between said second and fourth planes, said fifth plane being perpendicular to said first plane and convergent towards said third plane outwardly from the front end of the body, and a cutter offset angle greater than zero being defined between said third and fifth planes, the curved peripheral surface of the cutter roll being such that a generator thereof is inclined, in the region where the cutting edge contacts the outer wall of the seam, from the cutting edge toward said first plane, whereby when the abutment and traction roll are engaged on the top of the said can seam and the cutting edge with said outer wall thereof, and a said roll is rotated to effect relative circumferential movement between the opener and the can such that the centre of the cutter roll is behind the centre of the traction roll in the direction of relative movement of the can opener, the cutting edge engages the can seam outer wall at a angle thereto substantially equal to the cutter incline angle, to sever the outer wall, and the outer peripheral surface of the cutter roll lifts and peels radially inwardly the severed edge of the seam.

8. A power-driven can opener according to Claim 6 or Claim 7, wherein the motor is coupled with the traction roll so as to drive the traction roll.

9. A power-driven can opener according to any one of Claims 6 to 8, wherein the traction roll and the cutter roll are provided with intermeshing gear teeth whereby the roll driven by the motor drives the other roll in positive rotation.

10. A power-driven can opener having: a body including a carrying handle; a traction roll and a cutter roll, each rotatable about its own axis so that the rolls cooperate with each other to effect initial gripping engagement with a circumferential end seam of a can, and thereafter to grip and support the can by said end seam whilst rotating the can about an axis of the can the cutter roll progressively severing the can along a radially outwardly facing portion of the end seam, whilst the traction roll is driven rollably along an upwardly facing surface of the end seam, means for rotating at least one of the said rolls about its own axis, the position and orientation of the cutter roll being constant with respect to the body and the traction roll being resiliently biassed axially inwardly for limited, automatic outward axial movement in response to initial engagement of a can with the rolls, so that the rolls cannot otherwise move relative to each other except in the sense of rotation about their respective axes; and a fixed reaction guide element on the body for engaging the top of a double end seam of a can ahead of the said rolls in the direction of rotation of the can with respect to the can opener, whereby to guide the can in its rotation about its own axis and to exert a reaction force thereon, separate actuable means for effecting said initial gripping engagement being absent.

11. A power-driven can opener according to Claim 10, having two fixed guide elements on the body for engaging the top of the said can seam, said elements comprising, as the first guide element, the said reaction guide element a head of the rolls, and as the second guide element a projection which is behind the said rolls in the direction of rotation of the can with respect to the can opener whereby to guide the can into initial engagement with the traction roll and cutter roll.

12. A power-driven can opener according to Claim 10 or Claim 11, wherein the body defines a front end and a rear end of the can opener, the traction roll, cutter roll and said fixed guide element or elements being situated at the front end with the guide element or elements projecting forwardly of the body.

13. A power-driven can opener according to any one of Claims 10 to 12, wherein the said guide element, or at least one of said fixed guide elements as the case may be, is in the form of a fin.

14. A power-driven can opener according to Claim 11, or Claim 12 when dependent on Claim 11, wherein the fixed guide elements are in the form of fins having respective surfaces for engaging the top of a double end seam of a can, the said can-engaging surfaces being in planes defining a shallow acute angle between them.

15. A power-driven can opener according to Claim 10 or Claim 11, wherein the cutter roll has a curved peripheral surface terminating in a circumferential cutting edge for engaging a circumferential outer wall of the double end seam of the can, the traction roll having a peripheral surface for engaging on the top of the said can seam, the peripheral surface of the traction roll being tangent to a first plane substantially containing a can-engaging surface of the reaction guide element, the cutter roll being on the opposite side of the said first plane from the traction roll, the traction roll further having a chuck wall engaging surface for engaging a chuck wall of the said seam, the axis of the traction roll defining the intersection between a second plane, parallel to said first plane, and a third plane perpendicularto said first plane, said third plane being radial with respect to the can, the axis of the cutter roll defining the intersection between a fourth plane and a fifth plane, said fourth plane being perpendicularto said third plane and divergent from said second plane outwardly from the body, a cutter incline angle in the range 100 to 300 being defined between said second and fourth planes, said fifth plane being perpendicular to said first plane and convergent towards said third plane outwardly from the body, and a cutter offset angle greater than zero being defined between said third and fifth planes, the curved peripheral surface of the cutter roll being such that a generator thereof is inclined, in the region where the cutting edge contacts the outer wall of the seam, from the cutting edge toward said first plane, whereby when the abutment and traction roll are engaged on the top of said can seam and the cutting edge with said outer wall thereof, and a said roll is rotated to effect relative circumferential movement between the opener and the can such that the centre of the cutter roll is behind the centre of the traction roll in the direction of relative movement of the opener, the cutting edge engages the can seam outer wall at an angle thereto substantially equal to the cutter incline angle to sever the outer wall with a cutting force having a substantially minor radial component and the outer peripheral surface of the cutter roll lifts and peels radially inwardly the severed edge of the seam.