GB2141516A - Ratchet and pawl mechanism - Google Patents

Abstract

A ratchet and pawl mechanism, for a programmed control device of the kind having a rotatable element rotation of which controls operations of the appliance utilizing the device, comprising a pawl and ratchet tooth arrangement 5, 8 for rotating said element in a series of steps, a pivotable member 2 for moving said pawl 5 to coact with said ratchet teeth 8, and a load cam 1 operable to cause oscillatory pivotal movement of said member 2, said pawl 5 and said pivotable member 2 co-operating with one another adjacent the pivot axis 3 of said member 2 and said member 2 including a substantial mass 10 remote from said pivot axis 3 and being formed from a material of high density. <IMAGE>

Description

SPECIFICATION Rapid actuation mechanism This invention relates to a rapid actuation mechanism for programmed control devices, such as those used in various electrical household applicances.

A known form of programmed control device used in appliances such as washing machines, dish washers and driers includes at least one disc or cam drum as the programme support element, which, advancing through a series of stages, operates sequentially a series of electrical contacts, either switches or commutators, whereby the different operative stages of the appliance are controlled.

The movement of the programme support element for sequentially controlling the different operative stages of the appliance can be effected in either of two ways; in the form of slow drive, or a rapid stepped drive in which each advance step takes place almost instantaneously.

The rapid drive mode offers a series of advantages compared with the slow drive mode, for example The stepwise movement of the programme support element is independent of the working of the drive motor driving the element in that rapid actuation devices are nearly always based on springs which are loaded slowly, through the effect of a load cam, driven by the drive motor, and which, at a given moment, instantaneously transfer their energy, irrespective of the running of the motor at that moment.This means that it is unnecessary to provide "step contacts" to guarantee the power supply to the drive motor during the execution of the step movement, since a number of the contacts operated by the support element are involved in the power supply to the drive motor and often the change of state of a number of them will coincide in the same steps. In the event of it being necessary to dispense with the so-called "step contact" in the slow drive arrangement then the disc or cam drum has to be manufactured with much greater precision than that which is required of the rapid drive arrangement.

As the electric contacts are driven almost instantaneously, they have a low erosion rate which results in saving in costs and a longer working life.

The level of radioelectric interference generated is very small, due to the shorter duration of the electric arcs generated during the change of state of the contacts and, furthermore, the different interference signals corresponding to the different interruptions of the various contacts which are operated in the same step of the disc or drum, are produced within such a short space of time that, in accordance with different international standards in force, they are considered as a single interference signal, which permits a considerable economic simplification in the "anti-noise" filter of the machine for which the programmed control device is intended.

Against the many substantial advantages which the rapid actuation mechanism offers compared with the slow actuation system, the former does, however, have a very important disadvantage in that it is more difficult to control with accuracy the positioning of the programme support element at the end of the step movement. This is due to the fact that in the rapid actuation mechanism it is necessary to accumulate sufficient energy to overcome, in the hardest steps, the resistance to movement of the programme support element offered by a number of electric contacts, a pawl or equivalent positioning device, and other elements which may have to be driven, such as cams for the mechanical drive of devices for distributing water to the different compartments for detergents, additives, etc., whereas in the weaker steps it may be that only the resistance of the positioning pawl has to be overcome.Consequently, as the hardest steps have to be overcome reliably, the problem arises in the weaker steps of ensuring that the disc or cam drum does not advance more than a single step, due to the surplus energy stored in the drive device which is transferred in the form of kinetic energy to the whole of the parts intervening in the execution of the step movement.

The current technology offers a number of solutions to solve this problem, among which may be mentioned the use of kinematic chains whose speed decreases as the step advances and which have a zero velocity point when the step ends; the use of step devices whose surplus energy is transmitted by shock and/or thrust to an element, such as a pawl, lever, etc. for braking the disc or cam drum; the use of rocker devices which cause the blocking of the movement of the disc or cam drum at the end of the movement step, to release it a moment later, in order to make further steps possible normally, or to permit the manual operation of the device; and the use of devices which contribute towards increasing the resistance to movement of disc or drum during the weakest steps, to tend to render them equal to the hardest steps and in this way to achieve a uniform performance of the system in each and all of the steps.

It is doubtful that some of these solutions would prove effective, and they would present problems regarding the difficulty of definition or the balance sought. We can consider that the most effective solutions are those in which the programme support element has achieved a reduced level of kinetic energy at the end of the step run and, in this sense, a braking system is known whereby the drag movement velocity of a kinematic chain is reduced through a flywheel equipped with a gearing, to which a drag latch is coupled, the latch having a toothed area for this purpose. The latch when pushed sharply is braked by the turning resistance of the inertia flywheel, to which it is coupled through the toothed area of the latch, which meshes which the pinion gear wheel connected to the said flywheel.

This solution which is acceptable from a functional point of view, does however involve greater structural complexity, with the consequent increase in cost which this entails.

An object of the invention is to provide a rapid actuation system wherein the step by step movement of the programme support element is achieved, with optimum accuracy and with great structural simplicity.

In accordance with the present invention, there is provided a rapid actuation mechanism, for a programmed control device of the kind having a rotatable element rotation of which controls operations of the appliance utilizing the device, comprising a pawl and ratchet tooth arrangement for rotating said element in a series of steps, a pivotable member for moving said pawl to coact with said ratchet teeth, and a load carm operable to cause reciprocatory pivotal movement of said pivotable member, said pawl and said pivotable member co-operating with one another adjacent the pivot axis of said member and said member including a substantial mass remote from said pivot axis and being formed from a material of high density.

The above mechanism thus employs an actuating member itself having a high inertia so as to achieve reliable operation without having to resort to additional braking elements, such as the aforementioned inertia flywheel, for example, thereby achieving a reduced drive speed.

Since the pivoting member has a substantial mass in an area remote from its pivot axis and at the same time, the pawl co-operates with the member at a point near the pivot axis there arises an alternating slow backward and sudden forward movements, of the member and the pawl which makes the disc or cam drum advance step by step, through the tooth formation at its periphery or on a cogwheel rigidly joined to said disc or drum.

Preferably a further positioning pawl coacts with said ratchet teeth or further teeth to detain and correctly position the rotatable element both at the end of the step runs and the manual operation runs to select working programmes of the appliance utilizing the device.

It will be understood that for a given amount of available energy, the displacement velocity of the pivotable member and, consequently, of the whole system, including the disc or cam drum, depends to a great extent on the mass of the member and its distribution; the greater its inertia moment, the less its velocity, since: E= 1/2 lw2 in which: E = energy I = moment of inertia of the member and w = the angular velocity of the member.

The distribution of a relatively important mass in an area far from the pivot axis contributes to a considerable extent to the fact that the moment of inertia is high, as deducted from the following: I = . r2 in which: m = pointwise mass r = distance at which each pointwise mass stands from the pivot axis, since the factor r is squared.

As said member and said pawl co-operate adjacent the pivot axis of the member, then for a given angular velocity (w) of the movement of the member, the linear velocity (v of the displacement of the pawl is relatively small, since: V=w. r in which: r = the distance from the pivot axis of the member to the point at which the pawl and the member co-operate.

As mentioned above, in programmed control devices, the resistance to rotation is mainly determined by the application for which the device is intended, i.e. by the number of cams, whether or not they include mechanical drive cams, etc.; it is also determined by the construction layout, depending on the contact system, whether it concerns a disc or cam drum, whether the system is rapid or flow drive etc. and, finally, by the resistance opposing said further pawl or built-in positioning elements.

In a preferred arrangement a spring has to accumulate a certain amount of surplus energy, necessary to guarantee correct working, apart from the energy strictly necessary to overcome the resistance of the hardest step. This surplus energy is transmitted in the form of kinetic energy to the moving parts intervening in the execution of the step movement, producing an acceleration of these parts.

The energy balance at the end of the step run would therefore be as follows: S.E. = K.E. element + K.E. rest + K.E. member in which S.E. = Surplus Energy in the minimun resistance K.E. element = Kinetic energy of the disc or cam drum.

K.E. member = Kinetic energy of the lever or equivalent member.

K.E. rest = Kinetic energy of the rest of the moving parts.

K.E. element = 1 /2 1 element (V/R)2 K.E. member = 1/2 I member. (V/r)2 K.E. rest = 1/2 (m,v,2 + l3w32 + . .) = = 1/2 mv2 in which I element = moment of inertia of the disc or cam drum I member = moment of inertia of the lever or equivalent pivotable member.

V = Tangential velocity in the periphery of the disc or cam drum, equal to the linear displacement velocity of the pawl.

m = mass applied in the periphery of the disc or cam drum which would have energy equal to "KE rest".

Since: S.E. = K.E. element + K.E. member + K.E. rest it would be converted into: S.E. = 1/2 1 element (V/R)2 + 1/2 I member (V)2 + 1/2 mV2 r equals: 1/2 (1 element/R2 + I member./r2 + m)V2 in which for the purpose of transforming angular movement into linear movement: I element/R2 = equivalent mass of the disc or cam drum.

I member/r2 = equivalent mass of the lever or equivalent pivotable member.

In the last equation we can see that, for an amount of surplus energy, S.E., the velocity V drops as the sum I element/R2 + I member/r2 + m increases. In the equation, we want the value of the "equivalent mass" of the member (moment of inertia of the member/square of the distance between the pivot axis and the point of co-operation of the pawl and the member) to be small, so that with a given velocity (V) the minimum amount of energy possible is accumulated, thereby helping to detain the member, provided the step run has been completed. On the other hand, the addend (m) depends to a great extent on the construction features of the appliance and allows little operating margin, except unless additional elements are introduced, which enable their value to be altered significantly.

The preferred mechanism disclosed enables comparatively high values of I member/r2 to be obtained, compared with known systems, thereby reducing the drive velocity of the mechanism, to levels which enable the device to work highly satisfactorily, when the following condition is met: I member.,'r21 30 grammes.

Finally, the energy acquired by the pivotable member is neutralized at the end of the step, by impact against a fixed stop.

To complete the description of the preferred embodiment, and in order to asist a better understanding of the features of the invention reference is made to the accompanying single drawing. The drawing is schematic and shows a simple example of the invention which can constitute the basis for more complex solutions which may include, for example, timer systems to obtain different stopping times between the different step movements, without affecting the essence of the invention.

In the drawing, the two end working positions of the system have been illustrated in continuous and dotted lines.

Referring to the drawing it can be seen that the load cam 1, which is driven by a motor with its respective transmission, not shown in the figure, acts on the lever 2, making it pivot about axis 3; this lever 2 passes from the position shown with a continuous line to the position illustrated with a dotted line, all against the action of the spring 4.

A pawl 5 is coupled to the lever 2 at a point 6 close to the pivot axis 3, so that this pawl can turn with respect to the lever about said coupling point 6.

It should be noted that the pawl 5 need not necessarily be articulated to the lever, and can be independent, provided it is pushed by the lever.

A spring 7 keeps the pawl in contact with the ratchet teeth 8 of a wheel 9 firmly connected to the disc or cam drum, or on the actual toothed edge of said cam drum, as the case may be.

When the load cam 1 reaches the position shown with the dotted line, the spring 4 acts on the lever 2, suddenly to return the lever to the position shown with the continuous line, making the toothed wheel 9 advance one step by way of the pawl 5. Each step is equivalent to the gap between two consecutive teeth.

As already disclosed above, and can be gathered merely by observing the figure, the lever is provided with an important concentration of mass in its area 10 far from its pivot axis 3, so that the acceleration produced by the impulse spring 4 is minimal, thus achieving a slow and sure movement for the pawl 5, slow, due to the proximity of pawl to lever co-operation point 6 to the pivot axis 3 of the lever, and sure, due to the great mass of inertia of the lever.

A positioning pawl 11, assisted by a spring 12, contributes towards detaining and positioning the wheel 9 and/or the disc or cam drum, (not shown in the figure) both at the end of the step runs and at the end of the manual operation runs, for selecting the work programmes of the machine.

To complete the structure disclosed, a fixed stop 1 3 is provided to absorb the energy of the lever at the end of the step run.

The lever 2 or an equivalent pivoting member has a high moment of inertia. To obtain this, materials with a high specific weight will preferably, although not exclusiveiy, be used in the construction of the lever. For example, iron, brass, lead, zamak may be used in order to ensure minimum dimensions for this lever, which is especially important, taking into account the very limited space available in this type of device, while achieving the desired high mass.

Claims (9)

CLAIMS:

1. A rapid actuation mechanism, for a programmed control device of the kind having a rotatable element rotation of which controls operations of the appliance utilizing the device, comprising a pawl and ratchet tooth arrangement for rotating said element in a series of steps, a pivotable member for moving said pawl to coact with said ratchet teeth, and a load cam operable to cause reciprocatory pivotal movement of said pivotable member, said pawl and said pivotable member co-operating with one another adjacent the pivot axis of said member and said member including a substantial mass remote from said pivot axis and being formed from a material of high density.

2. A mechanism as claimed in claim 1 wherein said load cam causes reciprocating movement of said pivotable member by moving the member in one direction against a resilient bias and then releasing the member for movement in the opposite direction under the action of said resilient bias.

3. A mechanism as claimed in claim 1 or claim 2, wherein said pivotable member is a lever having said substantial mass at an end remote from the pivot axis.

4. A mechanism as claimed in ay one of claims 1 to 3, wherein the "equivalent mass' of the pivotable member (moment of inertia of the member/the square of the distance between the pivot axis and the point at which the pawl and said member co-operate) is equal to or more than 1 30 grammes, so that the concentration of mass existing in the pivotable member at a point far from its pivot axis, and the proximity to the pivot axis of the point at which the pawl and said member coact, determine a high moment of inertia, which in ttirn determines a reduced angular velocity, slow displacement of the pawl and a considerable supply of energy to the displacement of the pawl.

5. A mechanism as claimed in any one of claims 1 to 4 wherein the action of the pawl and the ratchet teeth arrangement is controlled by a timer system, either forming part of the control device or separate therefrom.

6. A mechanism as claimed in any one of claims 1 to 5, wherein the displacement of said pivotable member in a direction to advance said element is limited by a fixed stop dissipating surplus energy.

7. A mechanism as claimed in any one of the preceding claims, wherein said ratchet teeth are formed on said rotatable element.

8. A mechanism as claimed in any one of claims 1 to 6 wherein said ratchet teeth are formed on a wheel drivingly connected to said rotatable element.

9. A rapid actuation mechanism substantially as hereinbefore described with reference to the accompanying drawing.