ACTUATOR WITH VARIABLE MECHANICAL AMPLIFICATION AND ASSOCIATED METHOD

Description

Technical field

[0001] The invention relates to a variable mechanical gain actuator, and more particularly to a method for optimizing the kinematics relating to the variable mechanical gain actuator. Prior art

[0002] It is known from European publication EP1370388B1 to provide a drive device for the relative movement of two members which is capable of providing a variable kinematic ratio. The drive device is capable of being electrically controlled by a digital control system. Thus the drive device comprises as illustrated in figure 1 : a screw 10 in one step P1 given suitable for being driven in rotation around an axis, in one direction or in an opposite direction, under the action of a motor M, a nut 12 cooperating with the screw 10 and suitable for being driven in translation in the direction of the axis of the screw10, the nut 12 being integral in translation with one of the two organs, a socket 32 surrounding the screw 10 in axial direction XX of the screw 10, in the socket 32, first means of guidance 34L defining a linear guide parallel to the screw axis 10 to lock the rotation of the nut 12 in a first phase of movement of the nut 12, second guidance means 34H defining a helical guide which extends along the axis of the screw 10 and which has a reverse pitch compared to the pitch of the screw 10 to allow rotation of the nut 12 in the same direction of rotation as the screw 10 in a second phase of movement of the nut 12 where, for example, the two organs are closer to each other than in the first phase of movement, which makes it possible to reduce the apparent pitch of the screw10 and therefore the translational speed of the nut 12 in this second phase of movement.

[0003] The invention thus provides a drive device with variable kinematic ratio, which consists of two distinct parts: a first part where the nut 12 is locked in rotation and a second part where the nut 12 is rotated in the same direction as the screw 10.

[0004] Thanks to the first part, the screw 10 provides a kinematic connection during a first phase, which can be described as the inertial phase of the movement.

[0005] During this first phase, the nut 12 which is mounted free in translation is guided in rotation by the first guide means 34L which are fixed and parallel to the axis of the screw 10 and which therefore prevent the nut 12 to turn, regardless of the direction of rotation of the screw10 and that of the force to be transmitted. During this inertial phase which allows the two organs to come together or move apart (for example, closing and opening of a clamp), the screw will generally turn at a constant established speed. The translation speed (linear speed) of the nut 12 is therefore conditioned by the angular speed and the pitch of the screw 10.

[0006] During the second phase of movement, the second guide means define a helical guide 34H which forces the nut 12 to rotate in the same direction as the screw 10, which reduces the apparent pitch of the screw 10.

[0007] Therefore, assuming that the screw rotates at the same angular velocity as during the first phase of the movement, the nut 12 will then move at a lower speed, imposed by the apparent pitch. In fact, the nut 12"liberated" from the linear guidance of the first guidance means 34L will follow the steps of the second means of guidance 34H.

[0008] Thus, during this second phase of movement, the translation speed of the nut 12 decreases until it eventually becomes zero. We therefore have an apparent variation in the step until a zero value is obtained, if necessary.

[0009] In the device of the prior art, the peaks of the variations in the desired thrust force undergo maximum values ​​so that these impose the definition of the device, requiring an engine torque value allowing the maximum values ​​of the cycle to be reached. Technical problem

[0010] The invention aims to optimize the kinematics defined in the variable mechanical gain actuator device of the prior art described above. Summary of the invention

[0011] In a first aspect, the invention provides an actuator for providing a thrust force over a determined stroke, comprising a nut, a screw, a sleeve configured to surround the screw in an axial direction (XX) of the screw, a plurality of rollers, the nut being configured to cooperate with the screw, the nut being integral with the rollers, free to rotate, the rollers being configured to move each in particular in one of at least one helical guide of the sleeve, the screw being configured so that when it is turned it operates the actuator, to rotate the nut when it bears via the rollers on a profile of the helical guide and thus advance in the axial direction (XX) of the screw more or less quickly following a slope of the profile of the helical guide. The actuator further comprises a motor configured to turn the screw.Successive values ​​of the slope along the profile(s) of respectively one or more of the helical guides are adapted to ensure that the slope systematically compensates for at least one peak of the desired thrust force in order to clip the maximum values ​​of the thrust force so that the motor, the screw and the nut are dimensioned on a motor torque value corresponding to the value of the thrust force after clipping.

[0012] In a preferred embodiment, the slope along the profile of the helical guide is at each of its points inversely proportional to the force intended to be supplied at each of the respective points, thus configuring the actuator so that a driving torque to be supplied on the screw to obtain the force intended to be supplied is constant and equal to an average value which in the displacement brings the energy necessary to carry out the displacement operation.

[0013] In yet another preferred embodiment, the slope along the profile of the helical guide is configured to follow a hyperbolic law, thereby configuring the actuator so that by applying a constant torque to the screw, this results in a force applied by the actuator which increases linearly from 0 to its maximum value.

[0014] In yet another preferred embodiment, the actuator comprises one or more helical guides, and furthermore none, one or more rectilinear guides, each helical guide having its own variable slope profile, the number and distribution of said rectilinear and helical guides of the actuator, as well as the profile of each of the helical guides individually being determined according to the positioning and the value of different loads on the stroke of the actuator.

[0015] According to a second aspect, the invention provides a method for optimizing at least one slope of the profile of a helical guide in an actuator as described above, comprising a definition of a function F(y) of a force F to be provided by the actuator as a function of the stroke y traveled by the actuator; a determination of the slope Py of the helical guide at each position y as being inversely proportional to the force F(y) at this position y, for a constant torque C of the motor (M) according to the formula Py = C / F(y); and a determination of a predetermined energy value E ω in Joules to be provided on a rotation of the nut of ω radians as being linked with the constant torque C in Newton-meters according to the formula C = E ω / ω. Brief description of the drawings

[0016] The invention will be better understood by means of the detailed description of exemplary embodiments of the invention, and with reference to the figures, in which [ Fig 1] illustrates a prior art variable mechanical gain actuator device; [ Fig 2 ] contains a graph showing a force F which varies linearly from 0 to 10,000 N over a stroke of 2 mm according to an example of the invention; [ Fig 3 ] contains a graph illustrating the slope of a guide in a mechanical gain actuator device, as a function of the stroke according to an example of the invention; [ Fig 4 ] contains a graph illustrating the guidance profile obtained by applying the slope calculation of the figure 3 on a rotation of 2.5 radians; [ Fig 5 ] contains a graph illustrating a constant motor torque as a function of an angle; and [ Fig 6 ] contains a flowchart to illustrate a method of optimizing at least one slope of the profile of a helical guide in an actuator.

[0017] The same references may be used to designate the same or similar elements that appear in more than one figure. Detailed description

[0018] The optimization of the kinematics defined in the variable mechanical gain actuator device described in publication EP1370388B1 is done by a variation of the mechanical gain of the kinematics, which corresponds to the addition of an additional adjustment parameter compared to the device of the prior art. figure 1 incorporates basic elements known from the aforementioned patent EP1370388B1.

[0019] An engine M directly drives a ball screw 10 in a first organ 30. The ball screw 10 must have very good reverse efficiency. A nut 12 collaborates with the ball screw 10, this nut 12 is attached to a first part 14 which transmits the thrust to a subassembly36 which is actually a second organ that delivers output thrust. Ball bearings and a guide 24 provide guidance for a second part 42 of the second member which provides an output thrust force over a determined stroke (the determined stroke is not illustrated in the figure 1 ). The nut 12 also carries a plurality of pebbles 28 which are attached to it but free to rotate. The rollers 28 each roll in a guide which may have a rectilinear part 34L, and which has a helical part 34H whose pitch is reversed compared to that of the ball screw 10. This is the helical part 34H guides which provide almost all of the force generation for which the device was designed, the rectilinear part 34L essentially ensuring the approach.

[0020] The pitch of the screw 10is large so that its inverse efficiency is good and that an axial force applied to the nut 12 is sufficient to cause the nut to rotate 12 on the screw 10. This allows us to consider - in the following analysis - that the axial force generated by the screw 10 is negligible compared to the axial force produced by the rollers 28 when these pebbles 28 are in the helical guides 34 H. When the pebbles 28 are in the helical guides 34 H, the rotation of the nut 12 compared to the screw 10 allows the nut to move 12 to let it follow the guidance profile 34H.

[0021] The present invention involves an analysis of the slope along the profile of the helical portion 34Hguides in order to adapt the variations in the slope along the profile of these guides to the effort to be provided and thus to optimize the kinematics and the motorization to make the kinematic motor assembly of the variable mechanical gain actuator device the smallest, lightest, most efficient and least expensive possible.

[0022] By adapting the successive values ​​of the slope along the profile of the guides (34H) taken punctually, the objective is to ensure that the guidance (34H) systematically compensate for the peaks of the desired thrust force in order to achieve a real clipping of the maximum values ​​of the engine torque so that, unlike the device of the prior art, it is not these peak values ​​which impose the definition. This maximum value of engine torque will therefore be systematically lower than that established with normal kinematics which would correspond to the peak values ​​of the cycle.

[0023] The kinematic motor assembly thus defined will therefore be lighter, smaller and therefore less expensive than the prior art system, the motor will have fewer magnets (rare earths - samarium cobalt). Furthermore, the lower inertial level of the kinematic motor assembly will give this assembly a much higher level of performance, particularly for bandwidth.

[0024] If we can bring a constant torque to the motor, this will have the average value corresponding to the transfer, in the stroke of the cycle, of the energy necessary to carry out the expected function, it therefore corresponds to the minimum possible value of said motor torque.

[0025] As a general rule, if a constant torque is applied to the motor, it will be necessary to provide for occasional variations in the slope of the guides inversely proportional to those of the force to be delivered.

[0026] Thus, if the force to be delivered is proportional to the stroke, the slope of the guides 34H will have a hyperbolic law, so that the product of the force and the slope remains constant.

[0027] Thus the invention aims to optimize the profile of the guides 34H, this variation of the successive values ​​of the slope along the profile of these guides, therefore of the mechanical gain of the kinematic chain, corresponds to a real additional adjustment parameter compared to the device of the prior art. It is this specificity which makes it possible to ensure the expected function with a lighter, less expensive and more efficient motor and kinematics than that which can be achieved with the system of the prior art.

[0028] The same actuator may have none, one or more rectilinear sectors or rectilinear guides 34L and one or more sectors with variable slope or helical guides 34H, each sector with variable slope34H which can individually have its own profile. The number and distribution of said rectilinear sectors 34L and with variable slope 34H of said actuator, as well as the profile of each of the variable slope sectors 34H individually, are determined according to the positioning and the value of the different loads on the stroke of the load to be driven.

[0029] There figure 2 , given as an example, shows a force F which varies linearly from 0 to 10000 N over a stroke of 2 mm.

[0030] In this example, the force is given by the mathematical formula: F = K × Y Or F is the force in Newtons; K is the coefficient of the function in Newtons per meter - in the example 5 10 6 < Newtons per meter; Y is the stroke in meters - in the example 0.002 m; and x is the "multiplied by" sign.

[0031] According to the invention, the slope of the guidance at a given point is inversely proportional to the force at that point and the mathematical formula is Py = C / Fy Or Py is the slope of the guide at position Y in meters per radian; C is the engine torque in Newton meters; Fy is the force at position Y in Newton; and / is the sign for "divided by".

[0032] The energy W is the integral of the function 5 10 6< * Y, Y varying from 0 to 0.002 m, or 5 10 6< * (0.002) 2< / 2 = 10 Joules.

[0033] To obtain an energy value of 10 Joules on a rotation of 2.5 radians at constant torque, this constant torque must be 10 Joules / 2.5 radians = 4 Newton meters.

[0034] With this torque value of 4 Newton meters, the slope of the guide can be calculated at any point. And for example the following points: at position Y = 1 mm (mid-stroke), the force is 5000 N so the guide slope is equal to 4 / 5000 = 0.0008 m / radian; at position Y = 2 mm (end of stroke), the force is 10000 N so the guide slope is equal to 4 / 10000 = 0.0004 m / radian.

[0035] There figure 3 represents the slope of the guidance as a function of the stroke.

[0036] The start of the stroke, when the guide slope is greater than 4 mm / rad, is not shown. Indeed, for very low values ​​of force F, theoretically the slope of the curve becomes very large. But in practice and within the framework of the prior art device, the guide profile becomes rectilinear and parallel to the screw, and when the guides are rectilinear, it is the screw which ensures the displacement of the load. With a screw slope of 4 mm / radian, the force supported and supplied by the screw is 4 Nm / 0.004 = 1000 N, or 1 / 10th of the maximum force.

[0037] There figure 4 represents the guidance profile obtained by applying the calculation of the slope of the figure 3 on a rotation of 2.5 radians. The 0,0 point is offset from the axes for clarity.

[0038] The guide profile shown allows a constant torque of 4 Nm and by rotating the rollers in the guide through 2.5 radians, to apply an increasing force from 0 to 10000 N over a displacement of 2 mm.

[0039] There Figure 5 represents the engine torque which is constant.

[0040] Other examples could be given, such as a sinusoidally varying force. This is the case of an aeronautical flap or control surface which rotates around an axis perpendicular to the airflow, the axis of a flap is horizontal and the axis of a control surface is vertical. The master torque of a flap or control surface (the surface exposed to the airflow) varies sinusoidally as the angular position of the flap or control surface increases. The force exerted by the airflow is proportional to the master torque and therefore varies sinusoidally with the angle. To rotate the flap or control surface, a linear actuator acts on a point located at a certain distance from the axis of rotation. The force to be exerted by the actuator is sinusoidal and it will be very interesting to apply the present invention.In all cases, the calculation of the guidance slope at each point is carried out by dividing the motor torque by the force at this point; the motor can be sized on the average value.

[0041] There figure 6 contains a flowchart to illustrate the method of optimizing at least one slope of the profile of a helical guide in an actuator as described above. The method comprises the following steps: a definition 600 of a function F(y) of a force F to be provided by the actuator as a function of the stroke y traveled by the actuator; a determination of the slope 601 Py of the helical guide at each position y as being inversely proportional to the force F(y) at this position y, for a constant torque C of the motor (M) according to the formula Py = C / F(y); a determination of a predetermined energy value 602 E ω in Joules to be provided on a rotation of ω radians of the nut 12as being related with the constant torque C in Newton-meters according to the formula C = E ω / ω.

Claims

1. Actuator for producing a thrust force over a particular travel, comprising a nut (12), a screw (10), a bush (32) configured to surround the screw (10) in an axial direction (X-X) of the screw (10), a plurality of rollers (28), the nut (12) being configured to cooperate with the screw (10), the nut (12) being fastened to the rollers (28), free to rotate, each roller (28) being configured to move in particular in one of at least one helical guide (34H) of the bush (32), the screw (10) being configured so that when it is turned it causes the actuator to function to drive the nut (12) in rotation when it bears via the rollers (28) on a profile of the helical guide (34H) and therefore to advance in the axial direction (X-X) of the screw (10) more or less quickly depending on the slope of the profile of the helical guide (34H), the actuator further comprising a motor (M) configured to turn the screw (10), characterized in that successive values of the slope all along the profile or profiles of one or more respective helical guides (34H) are such that the slope systematically compensates at least one peak of the desired thrust force in order to clip maximum values of the thrust force so that the motor, the screw (10) and the nut (12H) are sized for a motor torque value corresponding to the value of the thrust force after clipping.

2. Actuator according to Claim 1 in which the slope all along the profile of the helical guide (34H) is at each point inversely proportional to the force to be supplied at each of the respective points, thus configuring the actuator so that a motor torque to be applied to the screw (10) to obtain the force intended to be supplied is constant and equal to a mean value which in movement provides the energy necessary to carry out the movement operation.

3. Actuator according to Claim 1 or 2 in which the slope all along the profile of the helical guide (34H) is configured to follow a hyperbolic law which, by therefore configuring the actuator so that applying a constant torque to the screw (10) produces a force applied by the actuator that increases linearly from 0 to its maximum value.

4. Actuator according to Claim 1 in which the actuator includes a helical guide (34H) or a plurality thereof and one or more rectilinear guides (34L), each helical guide (34H) having its own variable slope profile, the number and the distribution of the one or more rectilinear guides (34L) and the number and the distribution of the one or more helical guides (34H) of the actuator and the profile of each individual helical guide (34H) being determined as a function of the position and the value of various loads along the travel of the actuator.

5. Method of optimizing at least one slope of the profile of a helical guide (34H) in an actuator as defined in any one of Claims 1 to 4, comprising definition of a function F(y) of a force F to be supplied by the actuator as a function of the travel y travelled by the actuator; determination of the slope Py of the helical guide at each position y as being inversely proportional to the force F(y) at that position y for a constant torque C of the motor (M) in accordance with the formula Py = C / F(y); determination of a predetermined energy value Eω in Joules to be supplied over one rotation of the nut by ω radians as being linked to the constant torque C in Newton metres in accordance with formula C = Eω / w.