A roller screw drive with SAW (surface acoustic wave) - the sensor.

[0001] The present invention relates to the field of roller screw drives, enable, a rotational movement into a linear translation implement and vice versa.

[0002] Such a screw drive is provided with a screw, the has an external thread, a nut, arranged around the screw and has an internal thread, and a plurality of rollers in the longitudinal direction, the external threads have, the external thread and the internal thread of the screw or the nut with engaged.

[0003] Is advantageously the space, extending radially between the nut and the screw is found and in which the rollers are arranged, tightly closed and provided with lubricant, in particular with grease. This inner lubrication of the threaded drive allows, to limit the internal temperature of the threaded drive. The damage to the movable parts, in particular the contact surfaces of its thread, is reduced, the quality of mechanical rotation and/or translation to maintain - compound, the screw drive offers, . The life of the inner components of the threaded drive is increased and reduces the risk of fracture during operation in particular.

[0004] In a type of roller screw drives, planetary roller screw drive mentioned, the threads of the rollers and the thread of the nut have identical pitch angle on, but is different from that of the thread of the screw, such, that the rollers upon rotation of the screw relative to the nut and the screw to rotate about its own axis roll, without moving in the axial direction within the nut. The rollers are maintained parallel to the screw axis for rotation of crown, inner toothing having a synchronization, which communicates with outer teeth of said rollers in engagement.

[0005] It is well known, such a roller screw drive provided with means for, the measurement, monitoring and analysis of key sizes of movable parts in said screw drive to ensure. Knowledge of the value and a variation in the size, as the viscosity of the lubricant, allows, to evaluate the effectiveness of the threaded drive, wear and possible failure of the moving parts and its working conditions and determine and prevent them.

[0006] Due to the rotations of the movable parts and it is extremely complicated to each other accompanying shifts, incorporate sensors in a roller screw drive. Further the sensor must be disposed at a location, where it is in the transmission affects the magnitude and representative. In the case of measuring the viscosity is essential, that the sensor is located in the sealed radial space between the screw and the nut, which complicated its installation.

[0007] The present invention intends, to remedy this disadvantage.

[0008] The present invention particularly intends, to create a roller screw drive, the produce is simply an increased lifetime and has.

[0009] The invention relates to a roller screw drive, a screw with a includes external threads, a nut, the screw being disposed around and coaxially with said, wherein said nut has an internal thread, and a plurality of rollers, the radial clearance between the screw and the nut are arranged in a each have an external thread and, with said external thread of the screw and said internal thread of the nut is engaged. The rollers each also being provided at its ends with outer teeth, which are arranged axially on either side of the external thread. Further comprising the threaded roller pinion integral with the nut crown, inner toothing having a synchronization, which communicates with the external toothing of said rollers in engagement. A lubricant is provided in said radial gap.

[0010] According to the invention the nut is provided with at least one cylindrical inner surface, the axially between a crown and the internal thread of the nut is arranged. The roller screw drive also comprises at least one SAW (surface acoustic wave) - the sensor, to measure a physical quantity of the screw drive. Said sensor is provided with a solid support, are a first series of electrodes, which are arranged on said carrier and electrically energized can, to generate acoustic waves, propagating on a surface of the carrier, which is in contact with the lubricant, to be received by a second series of electrodes, which are axially spaced from said first row of electrodes on said support. Said at least one sensor is disposed in said at least one cylindrical inner surface of the nut.

[0011] According to another advantageous, but not compulsory features of the invention, individually or in combination:

• - the teeth are provided with synchronization each mounted on a threaded cylindrical portion of the nut not crown,
• - the crown being integrally molded with the nut, wherein the synchronization gears are formed in the nut,
• - the rollers are each provided at each end with a cylindrical pin, which projects from the external thread axially outwardly from,
• - the roller screw drive comprises two rings, which are each mounted radially between the screw and the nut and axially of the rollers, each provided with a plurality of continuous, cylindrical recesses on either side, regularly distributed in the circumferential direction and received in the interior of which the pins of the rollers are,
• - the physical quantity is, measured by the at least one sensor, the temperature, pressure or viscosity of the lubricant,
• - the solid support of the sensor for surface acoustic waves of piezoelectric material,
• - the sensor is mounted on the inner surface of a flexible printed circuit board, which is inserted into the cylindrical inner surface of the nut,
• - the nut axially on either side of the internal thread is provided with two cylindrical inner surfaces, wherein each of said surfaces is provided with at least one SAW sensor,
• - the first series of electrodes is intended, directly by electric cable, extending through the nut, to be connected to an electrical power supply,
• - is the first series of electrodes intended, indirectly, by radio waves, for example by a near-field communication system ("near field-communications" englich), be connected to an electrical supply,
• - the second series of electrodes is intended, directly by electric cable, extending through the nut, to be connected to a receiver.

[0012] The invention also concerns an actuator, a rotary drive and a roller screw drive according to any of the previously described embodiments comprises, wherein the screw is coupled to the drive.

[0013] The present invention will be better understood from the detailed description of embodiments, given as examples are not limiting, and in the attached Figures are represented. It show:

• - 1 an axially sectional view of a roller screw drive according to the invention,
• - 2 a view of the detail B 1,
• - 3 a sectional view along the axis I I of 1,
• - 4 a view of the detail a of the 3, and
• - 5 a top view of a screw drive of the SAW sensor 1.

[0014]Aplanetary roller screw drive (seconds. 1 to 4), which as a whole is designated with 10, comprises a screw 12 with the axis x12, 14 provided with an external thread, a nut 16, mounted coaxially around the screw 12 and is provided with a female thread 18, whose inner diameter is greater, than the outer diameter of the thread 14, and a plurality of rollers 20 in the longitudinal direction, the gap 22, the screw 12 and the nut 16 is limited radially from the, are arranged. The screw 12 extending longitudinally through a cylindrical bore of the nut 16, in which the inner thread 18 is formed. In a particularly advantageous manner the radial gap 22 is provided with lubricant, such as grease.

[0015] The rollers 20 are identical to each other and regularly distributed circumferentially about the screw 12. Each roller 20 extends along a screw axis 12 and has an external thread 24 x20 x12 axis parallel to, the external thread and the internal thread of the screw with the nut 16 14 12 18 engaged.

[0016] Each roller 20 further comprises at each end in the longitudinal direction an external toothing 26, 28 and a cylindrical pin 30, 32, the projects axially outwardly from the teeth. The teeth 26, 28 are arranged axially on either side of the external thread 24. The teeth 26, 28 each comprise a plurality of mutually identical, radial teeth, the regularly spaced in the circumferential direction. In the shown example are the outer surfaces of the teeth 26, 28 such threaded, the external thread 14 of the screw 12 to be engaged. In an alternative embodiment the outer surfaces of the teeth 26 can, 28 cylindrical, opposite the external thread 14 of the screw 12 radially offset portions be.

[0017] The threaded drive 10 is furthermore equipped with two crowns 34, 36 provided, the respective internal toothings 38 or 40 have. The crown 34, 36 are radially between the screw 12 and the nut 16 and arranged axially on either side of the internal thread of the nut 16 in the shown example are the crown 18 . 34, 36 each mounted on a non-threaded cylindrical portion of the nut 16. The bore of the nut 16 is stepped, around said crown 34, 36 having a smaller radial space requirement receive. The crown 34, 36 are integral with the nut 16 by any suitable means, for example by screws or rivets. In an alternative embodiment are the crown 34, 36 formed integrally with the nut 16, wherein then the internal toothings on the bore axially on either side of the internal thread 18 of the nut said nut 16 are formed. Each internal toothing 38, 40 with the external toothing of the rollers 26 or 28 is 20 for synchronization of their rotational movement about the screw 12 into engagement. The internal toothings 38, 40 of the crown 34, 36 are identical.

[0018] The threaded drive 10 further comprises two rings 42, 44, each thread 14 of the screw 12 and the nut 16 radially between the are mounted relative to the associated crown and 34, 36 are offset axially outward. Each ring 42, 44 in the axial direction is in a range of the corresponding crown 34, 36 mounted and circumferentially relative to said crown and said nut free. Each ring 42, 44 or 46 has several continuous cylindrical recesses 48 on, regularly distributed circumferentially and inside of which the cylindrical pin 30, 32 of the rollers 20 are received. So that the rollers 20 are circumferentially held at regular intervals. The threaded drive 10 also comprises snap rings 50, 52, each in a groove (not designated) are mounted, in a part of the corresponding crown 34, 36 is formed, and which are designed to, the corresponding ring 42, 44 to hold in the axial direction.

[0019] According to the invention is the nut 16 with two bore portions 54, 56 provided, have a cylindrical inner surface. A first cylindrical inner portion 54 is axially between the crown 34 and the internal thread 18 of the nut and a second cylindrical inner portion 56 is axially arranged 16 between the crown 36 and the female thread 18 of the nut 16 arranged. The two sections 54, 56 frame the thread 18 axially a. The cylindrical inner surfaces of the sections 54, 56 are radially offset with respect to the rollers 20, such, that it annular, axially on either side of the threaded radial gaps 18, 24 of the nut 16 or the roll forming.

[0020] The threaded roller pinion 10 also comprises two SAW sensors 60, 62 for measuring a physical quantity of the screw drive. The at least one sensor from the measured physical quantity is the temperature, pressure or viscosity of the lubricant in the radial gap 22 between the screw 12 and the nut 16, in which the rollers 20 are.

[0021] Only the sensor 62 is in more detail in the 2, 4 and 5 represented, because the sensor 60 is similar. The sensor 62 is provided with a solid support 64. The solid support 64 piezoelectric material advantageously consists. The support 64 is mounted on the inside of a flexible printed circuit board 70, the cylindrical inner surface of the portion of the bore of the nut 56 in 16 is arranged. The support 64 is advantageously integral with the plate 70, for example by adhesive bonding. The plate 70 is annular in section 56 of the nut 16 . 70 the plate advantageously is advantageously integral with said portion 56 connected, for example by adhesive bonding.

[0022] The sensor 62 also comprises a first series of electrodes 66, 64 are arranged on said support. These electrodes 66 can be energized electrically, to generate acoustic waves, extending across a surface of the support 64 spreading, in contact with the lubricant, from a second series of electrodes 68 to be received, the 64 are arranged on said support. The second series of electrodes 68 is arranged at an axial distance from the first series of electrodes 66, a surface acoustic wave propagation for the form.

[0023] The electrodes of the first row (not shown) with an electric power supply 66 outside the threaded drive 10 connected. Said compound can be directly, by electrical cable, extend through the nut 16, or indirectly by means of radio waves, for example by a system of the type near field communication (englich "near field-communications"). Said at least one sensor is disposed in said at least one cylindrical inner surface of the nut.

[0024] The electrodes (not shown) of the second row are 68 with a receiver connected outside the threaded drive 10. Similarly the compound can be direct or indirect.

[0025] The sensor operates in the manner described hereinafter. If the electrodes are electrically energized by a power supply 66 of the first row, said electrodes generating acoustic waves. These acoustic waves in the direction of the second series of electrodes 68 in wide axial spacing between the two rows 66, 68 and to the surface of the support 64 of piezoelectric material. These shafts so spread on a surface in direct contact with the lubricant from the physical conditions of said lubricant and therefore be influenced. In the case, where the viscosity of the lubricant to be measured is the physical quantity, the resonant frequency and the amplitude of the surface waves are directly in response to the value of the viscosity changed. The second series of electrodes 68 receives these acoustical wave after propagating. The characteristics of the wave, in particular the resonant frequency and the amplitude, this receiving electrodes 68 are then to a receiver outside the threaded drive 10 transmitted. These features of the received waves are then analyzed and the desired physical quantity of the lubricant can be derived by correlation.

[0026] The sensor 60 is mounted in the section 54 of the nut 16 has a similar construction and, as the sensor 62. thanks to the structure of the nut 16 with two cylindrical inner surfaces of the bore portions 54, 56 axially on either side of the internal thread 18, wherein each of said sections 54, 56 with at least one SAW sensor 60, 62 is provided, it is possible, in the two translational directions of the screw 12 a size of the threaded drive 10 and accurate measurements of the lubricant in the gap to 22.

[0027] The technical features of the various embodiments may also completely or only for some of them are combined. The roller screw drive may in cost, performance and simplicity of execution are adapted.