LINEAR STEPPER MOTOR WITH ROTOR SPINDLE FOR LINEARLY GUIDED ACTUATOR

Abstract

A linear stepper motor includes a rotor, two plain bearings, two motor bearing shields, a spindle nut, and a fork-shaped actuating rod. The rotor has a rotor shaft that comprises a motive thread and is configured to drive a linearly guided actuator. The rotor shaft has plain bearing journals at ends thereof, which each comprise an end radially and axially enclosed in the plain bearings seated in the motor bearing shields, and, by the motive thread, axially drives the spindle nut connected with the fork-shaped actuating rod in a rotation-proof manner. The rotor shaft includes a flexurally and torsionally rigid plastic threaded spindle with coaxially arranged metallic shaft ends so as to act as metallic journals on opposite ends for concurrent plain bearing support and axial support.

Claims

1. A linear stepper motor comprising a rotor, two plain bearings, two motor bearing shields, a spindle nut, and a fork-shaped actuating rod; wherein the rotor comprises a rotor shaft that comprises a motive thread and is configured to drive a linearly guided actuator, the rotor shaft comprises plain bearing journals at ends thereof, which each comprise an end radially and axially enclosed in the plain bearings seated in the motor bearing shields, and, by the motive thread, axially drives the spindle nut connected with the fork-shaped actuating rod in a rotation-proof manner; wherein the rotor shaft comprises a flexurally and torsionally rigid plastic threaded spindle with coaxially arranged metallic shaft ends so as to act as metallic journals on opposite ends for concurrent plain bearing support and axial support.

2. The linear stepper motor according to claim 1, wherein two metallic journals arranged coaxially at opposite ends of the rotor shaft form the two plain bearing journals and are fastened to the flexurally and torsionally rigid plastic threaded spindle with a plastic core.

3. The linear stepper motor according to claim 1, wherein a continuous metallic journal axle is guided through the plastic threaded spindle, and opposite end portions of the journal axle form the two plain bearing journals.

4. The linear stepper motor according to claim 3, wherein the plain bearing journals or the journal axle is connected to the rotor shaft in a rotation-locked manner.

5. The linear stepper motor according to claim 3, wherein the plain bearing journals or the journal axle is rotatable with respect to the rotor shaft.

6. The linear stepper motor according to claim 1, wherein a neck flange is molded on a non-drive side of the rotor shaft for a rotation-locked connection with a rotor magnet of the rotor.

7. The linear stepper motor according to claim 6, wherein by injection molding of the rotor shaft, the rotor magnet is insert-molded.

8. The linear stepper motor according to claim 1, wherein the motive thread is a trapezoidal thread.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 shows an example with two metallic journals as plain bearing journals.

[0008] FIG. 2 shows an example with a continuous journal axle for the plain bearing journals.

DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure will be described in detail in conjunction with the drawings. It should be noted that the figures are illustrative rather than limiting. The figures are not drawn to scale, do not illustrate every aspect of the described embodiments, and do not limit the scope of the present disclosure.

[0010] In one embodiment, the greatly schematized representation according to FIG. 1 depicts a linear stepper motor in cross section. Substantially, it includes a motor housing 1 with two bearing shields 2, 3 which close the housing 1 at its opposite ends, a stator 4, a rotor including a rotor magnet 5 and a plastic rotor shaft 6 having a motive thread 7 formed on it, and an actuating rod 8 of a fork-shaped design which is linearly operable by the rotor shaft 6 and which has a spindle nut 9 at its fork base to engage with the motive thread 7 of the rotor shaft 6. The spindle nut 9 can be formed directly at the actuating rod 8 or it is embedded in the fork base in a rotation-locked manner. The actuating rod 8 itself is guided by the drive bearing shield 3 in a rotation-locked manner. Outside the drive bearing shield 3, a customer-specific function head 10, which is, e.g., plugged on the two legs of the fork-shaped actuating rod 8, closes the actuating rod 8 axially. The rotor shaft 6 is supported by the two bearing shields 2, 3. The actuating rod 8 is guided on the rotor shaft 6, on the one hand, and by the drive bearing shield 3, on the other hand. Specifically, according to FIG. 1, the plastic rotor shaft 6 has coaxial metallic journals as plain bearing journals 11, 12 which are of high surface quality and are guided with wear resistance, low maintenance and minimum play in the bearing shields 2, 3 both radially by roller bearings 13, 14 and axially by means of a ball bearing 15, 16. On the non-drive side, the rotor shaft 6 is provided with a neck flange 17 which connects the rotor shaft 6 to the rotor magnet 5 in an especially rotation-locked manner. According to the disclosure, a rotation-locked connection between the plain bearing journals 11, 12 and the rotor shaft 6 is not a prerequisite because the rotor 6 can rotate relative to the plain bearing journals 11, 12 in another embodiment.

[0011] In an alternative embodiment, the linear stepper motor according to FIG. 2 has a design similar to the design of FIG. 1. However, the rotor shaft 6 differs from FIG. 1 by the fact that the two plain bearing journals 11, 12 are linked in form of a one-piece continuous journal axle 18 either of metal or consisting partly of separate plastic materials, running coaxially through the rotor shaft 6.

[0012] The disclosure is particularly suited for valve actuators.