WO1996035255A1

WO1996035255A1 - Low-cost synchronous or stepper motor

Info

Publication number: WO1996035255A1
Application number: PCT/FR1996/000670
Authority: WO
Inventors: Claude Oudet
Original assignee: Sonceboz S.A.
Priority date: 1995-05-04
Filing date: 1996-05-03
Publication date: 1996-11-07
Also published as: EP0824780A1; FR2733859B1; FR2733859A1

Abstract

A dual phase stepper motor is described, particularly for driving an indicator needle, of the type comprising a stator part formed by a main block (1) of a soft magnetic material connected to four magnetic cores (3-6) each supporting an electrical coil (14-17), and a cylindrical thin-walled rotor with 2N+1 pairs of magnetic poles radially magnetised, wherein the tip of the magnetic cores (3-6) is separated from the rotor only by a radial gap and two diametrically opposed cores are magnetised in opposite directions by coils (14-17) of the same phase. The magnetic flux is closed by a secondary block (30) on the opposite side from the magnetic cores (3-6) relative to the thin permanent magnet, and the number of magnetic pole pairs of the magnet is 2N+1, where N is 1 or 2.

Description

ECONOMICAL STEP OR STEP MOTOR

The present invention relates to a numerically controlled stepping motor intended in particular for driving the needles of measuring instruments and indicators, such as automobile on-board instruments.

Such motors are intended to replace the motor components controlled by analog signals, such as logometers or actuators with crossed coils. Such stepping motors must have a negligible torque without current and a torque due to the current represented by a sinusoidal function.

One seeks for such motors a high mechanical stiffness on the needle, for a theoretical position fixed by the ratio of the control currents of each of the phases, ie a significant increase in the return torque at this theoretical position when the the needle is removed for a reason such as an unbalanced needle or a friction torque. This stiffness can be obtained by a motor with a single pair of poles associated with a mechanical reducer, by an increase in the number of motor poles, or by the combination of a mechanical reducer and a multipolar motor. Such motors must have a low manufacturing cost and we therefore seek to limit the number of parts and wide manufacturing tolerances.

The object of the invention is to provide such an engine further having a low noise level, a low current consumption and a volume, and above all a reduced thickness.

We know in the prior art the French patent FR2677507 describing a motor comprising a first stator part cooperating with at least two electric coils, a second stator part ensuring at least partial closure of the magnetic fluxes and a rotor comprising 2N thin magnets transversely magnetized in alternating directions so as to present alternately positive and negative magnetic poles on each of its surfaces. The rotor comprises on each of its surfaces five pairs of poles and the first stator part consists of two identical stator parts of high magnetic permeability each having two stator poles joined by a middle part surrounded by a coil of a length substantially equal to the width of the opening of the stator part. Each stator part wound, with the area of the second stator part closing the flow, constitutes a phase of the stator of the two-phase motor. The center lines of the two poles are spaced about 1.5 paces apart. The second stator part is made of a material of high magnetic permeability having four zones corresponding respectively to the four stator poles, said four zones being connected in pairs so as to ensure the closure of the magnetic flux of each of the stator parts.

Such a stepping motor has a single plane of symmetry theoretically passing through the axis of rotation. The two air gaps corresponding to a phase are located on the same side of this plane of symmetry and the two air gaps corresponding to the other phase are arranged on the other side of said plane. This motor therefore has a certain sensitivity to a shift in the plane of symmetry relative to the axis of rotation of the rotor.

In addition, the radial forces due to the induction in the radial airgaps do not present a zero algebraic sum, except for particular levels of current. This can result in an alternating radial displacement of the rotor in its bearings generating noise.

Also known in the prior art is patent US Pat. No. 5,245,233 concerning a motor having a stator comprising four half-coils arranged symmetrically with respect to the axis of the rotor and supported by iron cores parallel to the axis of the rotor. The cores are magnetically coupled and supported by this cylinder head. The stator of the motor according to this embodiment has four plane of symmetry theoretically passing through the axis of rotation. The cores of the coils have armatures added at their ends and forming poles cooperating with the magnet.

In this document of the prior art, the ends of the coil cores of the same phase, therefore diametrically opposite, are magnetized in identical signs by the current. We also know the German patent

DE3918538 concerning a method for controlling a stepping motor. The described method consists in delivering, for a step to be carried out by the armature, a sequence of pulses in which the ratio of the durations of pulse and exposure in one period (T), increases from one pulse to the next. The number of current pulses (m) or their durations, in the sequence is (are) determined according to the inertia of a system so that to a large inertia corresponds a small number of long pulses sent to the coils (L1, L2) of the stepping motor while conversely, to a low inertia corresponds a large number of finely stepped pulses at high frequency. The stepping motor described in this document comprises a stator having four electric coils and a rotor comprises a pair of magnetic poles.

The aim of the present invention is to improve the performance of such two-phase motors by proposing a low-noise motor, accepting large manufacturing tolerances, and guaranteeing a torque in the absence of negligible current and a "torque-current" function of sinusoidal type.

To this end, the invention relates more particularly to a two-phase stepping motor of the type comprising a stator part formed by a main cylinder head made of a soft magnetic material connected to four magnetic cores each supporting an electric coil, and a shaped rotor cylindrical with thin wall presenting 2N + 1 pairs of radially magnetized magnetic poles. The end of the magnetic cores is separated from the rotor only by a radial air gap, two diametrically opposed radial air gaps being supplied by coils flat in the same phase and exciting the corresponding cores in the opposite direction of magnetization. The magnetic flux is closed by an auxiliary yoke disposed on the side of the thin magnets opposite the magnetic cores. The number of pairs of magnetic poles is 2N + 1 with N equal to 1 or 2. The variant with N = 2 is the preferred variant because it corresponds to the optimization of the torque per ampere-turn.

Unlike the motor described in US Pat. No. 5,245,233, the motor according to the invention does not have any part attached to the ends of the coil cores. The absence of such armatures makes it possible to eliminate a part, to facilitate assembly and to reduce the permeance of the magnetic circuit seen by each phase, therefore the section of the coil cores, while keeping very good field modulation due to current as a function of the angular position, which is favorable to the torque due to the current and to the reduction of the odd harmonics of this torque.

Furthermore, the use of 6 poles, and more particularly 10 alternating poles, makes it possible to reduce the reduction ratio of the mechanical reducer associated with the motor, which increases the reliability of the assembly.

The axes of the ends of the cores of the coils are in radial planes containing the axis of the rotor.

According to a preferred embodiment, the axes of the ends of the cores are oriented parallel to the axis of the rotor or perpendicular to the axis of the rotor.

According to another embodiment making it possible to reduce the thickness, the cores are arranged radially.

According to a first variant, the auxiliary cylinder head is formed by a cylinder made of a soft magnetic material secured to the rotor. According to a second variant, the auxiliary cylinder head is formed by a cylinder made of a fixed soft magnetic material placed inside the rotor and defining with the latter an internal radial air gap. Advantageously, the auxiliary cylinder head is magnetically connected to the main cylinder head.

According to a preferred embodiment, the rotor has on its inner and outer cylindrical surfaces 5 pairs of poles, ie 10 poles magnetized radially in alternating directions.

According to an alternative embodiment, the cores of the coils are parallel to the axis of rotation of the rotor.

Advantageously, the main cylinder head is formed by a base extended by four cores each supporting a wafer type coil, the rotor being articulated around an axis of rotation parallel to the cores passing through the center of said square and being positioned to define the air gaps with the terminal parts of the cores protruding from the electrical coils. According to a preferred variant, the main cylinder head is formed by a base extended by four perpendicular branches bent at 90 ° to form four cores of rectangular section each supporting a wafer type coil, the rotor being articulated around an axis of rotation parallel to the nuclei.

According to another variant, the main cylinder head is formed by a base further extended by a central cylindrical part, with an outside diameter less than the inside diameter of the rotor, and forming the auxiliary cylinder head.

According to another variant, the main cylinder head is formed by a base made of a soft material on which cores are magnetically coupled.

Advantageously, two opposite coils are supported by a molded plastic part constituted by two bodies having an inner section complementary to the section of the core, said bodies being connected to one of their ends by a connection zone having a hole for the passage of the axis of the rotor, said connection zone being flexible enough to allow the folding of the bodies so that their central axes are aligned during winding electric wire.

The present invention will be better understood on reading the description which follows, referring to the accompanying drawings in which:

- Figure 1 shows a view of the motor in cross section;

- Figure 2 shows a top view of the engine;

- Figure 3 shows a top view of the cylinder head; - Figure 4 shows a view of the molded part supporting the coils.

The stepping motor according to the example described with reference to the appended figures comprises a stator structure and a rotor. The stator structure is shown in section view in Figure 1 and in plan view in Figure 2. It comprises a main yoke (1) made of a soft magnetic material. This main cylinder head (1) has a base (2) in the form of a cross extended by four cores (3 to 6) extending perpendicular to the base (2) and parallel to the axis of rotation (7) of the rotor.

Figure 3 shows a top view of the main cylinder head. The cores (3 to 6) are arranged at the four corners of the base (2) in the general shape of a cross having four branches (8 to 11) perpendicular and of equal length, extending radially with respect to a central part (12 ) disc-shaped. The central part is pierced by a hole (13) to receive an axis (7) of the rotor. This axis is embedded in the cylinder head. In the example described, the cores are produced by deformation of the radial branches in order to straighten them by 90 ° relative to the plane of the base. The end (43 to 46) of the cores (3 to 6) facing the thin permanent magnet (29) is in the example described in the extension of the part of the core which supports an electric coil (14 to 17) in the shape of a cake. It is also possible to make a thinner motor, the cores being attached to a base by riveting or welding, the ends (43 to 46) of the cores being folded at 90 ° relative to the part of the core which supports an electric coil (14 to 17). Yet another variant consists in producing a main cylinder head comprising cores arranged radially in the plane perpendicular to the axis of the rotor.

The rotor comprises a cylindrical magnet (29) equivalent to ten sectors (18 to 28) in the form of radially magnetized tiles, in alternating directions so as to present a SOUTH pole, alternately on the interior surface and on the exterior surface of the rotor. Each of the magnetized sectors occupies an angular sector of 36 °. The cylindrical magnet can be produced by association of independent magnetic parts, or by magnetization of the various zones of a ring preferably produced by molding, by compression or injection in an alloy with high coercive field of plastic neodymium-iron, for example the magnets sold under the name "NP8L" by the company DAIDO STEEL CORPORATION and made from powder sold by the company GENERAL MOTORS under the name of "MQI". It is also possible to use a material with a radial orientation such as that sold under the name "SAMLET 9R" by the company EPSON. In the example described, the thickness of the magnet is one millimeter for a height of 2 millimeters and a diameter of the order of 10 millimeters. The air gap formed between the ends (43 to 46) of the main yoke and the outer surface of the thin permanent magnet (29) is about 0.4 to 0.5 millimeters.

The magnet (29) is integral, in the example described, with an auxiliary yoke (30) of annular shape, supported by a molded plastic part (31) having a crown extended by a foot (32) of tubular shape. The crown has a peripheral groove in which the auxiliary cylinder head (30) is housed by overmolding. The tubular leg (32) forms the rotation shaft concentric with the axis (7) embedded in the main cylinder head.

The coils (3 to 6) are mounted two by two on supports, an enlarged view of which is shown in FIG. 4.

The supports consist of deformable molded plastic parts, having two tubular parts (34, 35) extended at each end by annular shoulders (36 to 39). The upper annular shoulders (37, 38) of the tubular parts respectively (34, 35) are joined by a connecting part (40) flat, pierced by a central hole for the passage of the axis (7) of the rotor.

By folding this support, it is possible to align the axes of the tubular parts (34, 35), the connecting part then deforming to adopt as shown in Figure 4 a shape of "U". It is then possible to wind the wire from two opposite coils in order to supply them in series without having to cut the wire, in a single operation. The support is then returned to the position of use, by straightening the two tubular parts (34, 35) to make them parallel to each other. The connecting part (40) then takes the form of a flat tongue joining in a same plane the two lower flanges (37, 38).

The motor has two supports of this type, arranged perpendicularly and slid around the cores (3 to 6). The connecting parts (40) of the two supports overlap and in the example described have a central allowance.

The invention has been described in the foregoing by way of nonlimiting example, and it is understood that the person skilled in the art will be able to carry out numerous variants without going beyond the scope of protection. In particular, the cores can be produced by deformation of the branches of a part made of a soft material, or by riveting independent cores on a base.

Claims

1 - Two-phase stepping motor, in particular for driving the needle of an indicator, of the type comprising a stator part formed by a main yoke (1) made of a soft magnetic material connected to four magnetic cores (3 to 6) each supporting an electric coil (14 to 17), and a thin-walled cylindrical rotor having 2N + 1 pairs of radially magnetized magnetic poles, characterized in that the end of the magnetic cores (3 to 6) is separated from the rotor only by a radial air gap, two diametrically opposite cores being magnetized in opposite directions by coils (14 to 17) belonging to the same phase, in that the magnetic flux is closed by an auxiliary yoke

(30) disposed on the side opposite to the magnetic cores (3 to 6) relative to the thin permanent magnet and in that the number of pairs of magnetic poles of the magnet is 2N + 1 with N equal to 1 or 2.

2 - Two-phase stepper motor, in particular for driving the needle of an indicator according to main claim (1) characterized in that the auxiliary yoke (30) is formed by a cylinder made of a soft magnetic material integral with the rotor.

3 - Two-phase stepper motor, in particular for driving the needle of an indicator according to main claim (1) characterized in that the auxiliary yoke (30) is formed by a cylinder made of a soft magnetic material fixed disposed inside the rotor and defining with the latter an internal radial air gap.

4 - Two-phase stepper motor, in particular for driving the needle of an indicator according to any one of the preceding claims, characterized in that that the rotor has on its peripheral surface 10 poles magnetized in alternating directions.

5 - Two-phase stepping motor, in particular for driving the needle of an indicator according to any one of the preceding claims, characterized in that the ends (43 to 46) of the cores (3 to 6) are parallel to the axis of rotation of the rotor.

6 - Two-phase stepper motor, in particular for driving the needle of an indicator according to any one of claims 1 to 4 characterized in that the cores (3 to 6) are oriented radially.

7 - Two-phase stepping motor, in particular for driving the needle of an indicator according to claim 5 characterized in that the main cylinder head

(1) is formed by a base (2) extended by four perpendicular branches bent at 90 ° to form four cores (3 to 6) with rectangular section each supporting a coil (14 to 17) of wafer type, the rotor being articulated around an axis of rotation parallel to the cores (3 to 6).

8 - Two-phase stepper motor, in particular for driving the needle of an indicator according to claim 7 characterized in that the main cylinder head

(1). is formed by a base further extended by a central cylindrical part, with an outside diameter smaller than the inside diameter of the rotor, and forming the auxiliary cylinder head.

9 - Two-phase stepper motor, in particular for driving the needle of an indicator according to any one of claims 1 to 4 characterized in that the main cylinder head is formed by a base made of a material soft on which are magnetically coupled cores (3 to 6).

10 - Two-phase stepper motor, in particular for driving the needle of an indicator according to any one of the preceding claims, characterized in that two opposite coils are supported by a plastic support consisting of two bodies tubular (34, 35) having an inner section complementary to the section of the core (3 to 6), said tubular bodies (34, 35) being connected at one of their ends by a connecting part (40) having a hole for the passage of the rotor axis, said connecting part (40) being flexible enough to allow the folding of the tubular bodies (34, 35) so that their central axes are aligned during the winding of the electric wire.