GB1571878A

GB1571878A - Damping of a stepping motor

Info

Publication number: GB1571878A
Application number: GB1785178A
Authority: GB
Original assignee: Mannesmann VDO AG
Current assignee: Mannesmann VDO AG
Priority date: 1977-05-13
Filing date: 1978-05-04
Publication date: 1980-07-23
Also published as: FR2390851B3; DE2721621A1; FR2390851A1

Description

(54) IMPROVEMENTS IN THE DAMPING OF A STEPPING MOTOR (71) We, VDO ADOLPH SCHINDLING AG, of 103 Grafstrasse, Frankfurt/Main, Germany, a body corporate organized according to the laws of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates in general to a stepping motor and more particularly to a stepping motor, the rotor of which travels through a rotational path from a first step position to a second step position, the rotor being subjected to a damping force.

In the field of electric clocks and watches, the movements of both large and small timepieces are driven by stepping motors. Undamped stepping motors usually have the disadvantage that the rotor oscillates into a stationary stepping position, thus producing noises in the rhythm of the steps, usually one per second. Supplementary loading of the movement may thus occur. The useful value of a timepiece may be considerably reduced by the noises it makes particularly in the case of an alarm clock.

It is therefore desirable to eliminate noise by altering the characteristics of the approach of the rotor into the stepping position. For this purpose, it is known to damp the rotor movement for its entire path of rotation. However, this solution further reduces the efficiency of the stepping motor, which is already relatively poor. In particular, starting-up of the rotor from its stationary position becomes difficult. Furthermore, the frictional damping acting on the entire rotation path of conventional damping devices may reduce the accuracy of travel into a stepping position.

It is also known to couple inert mass elements with the rotor via a resilient element so as to prevent chatter of the gearwheels in a stepping motor. However, noise from the gearing is not reliably suppressed by this method, since the surplus energy which is present on arrival at a stepping position is merely converted to another form which under some circumstances may again react on the gearing.

Furthermore, use of this method presupposes especially careful construction of component parts.

It is an object of the present invention, whilst avoiding the above described disadvantages, to design a process for the damping of stepping motors in which noises due to travel of the rotor into its stepping positions are avoided but in which overshoot does not occur and the useful capacity of the stepping motor is as far as possible not reduced.

According to one aspect of the present invention there is provided a method of damping a stepping motor, the rotor of which rotates from a first stepping position to a second stepping position, wherein the movement of the rotor is damped only during part of its rotation between the two positions.

By using a process embodying the present invention the damping force can be applied so that the rotor approaches a stepping position in the desired manner, i.e.

the rotor does not overshoot or overshoots only to negligible degree.

In a preferred embodiment, the process is designed so that the damping force is applied to the rotor in a rotation zone before a stepping position, and is not applied at the stepping position or in a zone immediately adjacent to it. Thereby, the rotor is able to reach its stepping position, since prior to the stepping position the damping force is removed. The rotor is also able to start-up for movement into the next stepping position unhindered, since at this point there is no damping force to be overcome. Thus, the distinctive feature of this device is that damping occurs only when it is actually necessary for producing the desired approach characteristic and it does not hinder the movement of the rotor along the rest of its rotation path. With this arrangement, the damping force existing in the section of the rotation path in which it is to act on the rotor may also to advantage be of varying magnitude. The damping force is made to increase from zero to a maximum value and then fall off to zero again before the stepping position is reached.

According to a second aspect of the present invention there is provided the combination of a stepping motor and a device for damping the stepping motor, said stepping motor having a rotor which roates from a first stepping position to a second stepping position, said device including: a first damping means attached to the rotor, and a fixed second damping means; wherein the first damping means and the second damping means pass into engagement with each other in a rotational range which is smaller than the rotational path between the two stepping positions.

Preferably, the first damping means is a rotating wing attached to the rotor, and the second damping means is a viscous liquid provided in a trough. The rotating wing dips into the liquid only during part of its rotation path, but the trough, which is only partially filled with viscous liquid encloses, the entire range of rotation of the rotating wing. The viscous liquid may be oil. The rotating wing dips into the viscous liquid in the trough to a greater or lesser extent according to the position of the rotor in its rotation path. Thus the rotor is subjected to a varying damping force as it approaches a stepping position.

Since the trough encloses the entire rotation zone of the rotating wing, during transportation before assembly of a timepiece equipped with a stepping motor, the viscous liquid cannot escape the trough.

Sealing of the trough is relatively simple, since it is merely necessary to extend a rotating rotor shaft out of the housing.

Preferably, the device is constructed so that the trough has a rotationallysymmetric cross-section in a plane perpendicular to the motor axis, and a substantially V-form cross-section in planes extending radially from the rotor axis.

Thereby, the damping of the stepping motor is satisfactory even when the stepping motor is not in its optimum position but is installed within a predetermined pivoting range. Furthermore, the manufacture of the device with the rotationally symmetric trough involves relatively little expense.

In a stepping motor which has two stepping positions in its rotation path, the two rotating wings are preferably attached to the rotor so as to be diametrically opposite each other. Thus a rotating wing is able to dip into the same trough before the rotor travels into each of the two stepping positions. Also, due to the symmetrical arrangement of the roating wings, rotational movement of the rotor is not impaired.

In a further modified form, at least one external face of the rotor has a damping liquid adhering to it to form a first damping means. A second damping means is formed by a stationary flank in the rotation path of the rotor along which the damping liquid slides prior to the arrival of the rotor at a stepping position. Construction of this device is made easier if the damping liquid used adheres well to the face of the rotor. In this case, no special sealing measures are necessary.

Preferably the stationary flank projects an increasing amount into the rotation path of the face of the rotor to which the damping liquid adheres. In this way an increasing damping force related to the rotation velocity of the rotor is generated.

In a further preferred form, the damping liquid is a magnetic liquid which adheres to the pole faces of the rotor. In this way, the damping liquid is most effectively kept in the region of maximum magnetic field strength.

In a further preferred embodiment of th present invention, the damping liquid is replaced by a flexible plastics filament projecting from at least one external face of the rotor. The said plastics filament may be made from a plastics material which is abrasion-resistant and has the desired sliding properties.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawing which shows three embodiments of the invention in diagrammatic form and in which: Figure 1 is a section perpendicular to the rotor axis of a stepping motor having a first type of damping system; Figure 2 shows a stepping motor with the damping system of Figure 1, and is a section in the plane of the rotor axis: Figure 3 shows a section perpendicular to the rotor axis through a stepping motor having a second type of damping system; and Figure 4 shows a section as in Figure 3 through a stepping motor with a third type of damping system.

Referring to Figure 1, reference numeral 1 denotes a rotor of a stepping motor. The rotor is shown in a first stepping position relative to the stator winding 2.

Two rotating wings 3 and 4 are rigidly secured to the rotor 1, so as to be opposite each other. The wings 3 and 4 are offset by an angle relative to the stator so that in each stepping position one of the two rotating wings 3 and 4 projects completely out of an oil sump 5.

The oil sump 5 is formed by a trough in the interior of a housing 6. The trough is symmetrical about the plane of the rotor axis. Radial cross-sections through the trough have an approximately V-form shape. With this design of trough, the depth of the soil sump increases from zero to a maximum value and then falls to zero again when a rotation path is made in the direction of the arrow 8.

When the rotor 1, is in the position shown in Figure 1, neither of the rotating wings 3 and 4 is in contact with the oil sump 5 and so that rotor movement is initially undamped. Therefore when the rotor 1 starts to rotate towards the second stepping position, it does so with the maximum possible torque. However, as the rotor approaches the second stepping position, the rotating wings 4 dips into the oil sump so that the rotational movement of the rotor is first of all weakly and then more strongly damped. Shortly before the rotor reaches its second stepping position however, the rotating wing moves out of the lowest position of the sump into the shallower portion thereof, so that the damping force is reduced and finally falls to zero in the second stepping position.

Thus, no damping force is present at the second stepping position to hinder the rotor's approach to that position. In the second stepping position, the rotating wing 4 occupies the position of the rotating wing 3 shown in Figure 1. Figure 1 furthermore shows that free, undamped movement takes place within sections 9 and 11 of the entire rotation path, whereas in sections 10 and 12 the rotational movement is damped.

Referring to Figure 3, end faces 13 and 14 of a rotor 1 each have a coating of viscous magnetic liquid. The coatings are denoted by the numerals 15 and 16. A housing 22 encloses a stator winding 2 and has a substantially circular inner recess 17. Flanks 18 and 19 extend into the sections of the rotation path of the rotor 1 to be damped. The flanks 18 and 19 protrude into the inner chamber of the recess far enough to engage with the viscous liquid, but not with the solid body of the rotor 1. The projection of the flanks into the recess increases during part of the rotation path of the viscous liquid and then decreases to zero before the stepping posi tion of the rotor is reached.

With this arrangement, damping of the rotor movement similar to that in the em bodiment shown in Figure 1 is achieved.

However, just before reaching each of the two possible stepping positions, both of the flanks and their associated magnetic liquid coatings interact simultaneously and so their damping forces are combined in their effect. Additionally, there are the damped, sections in Figure 3, as is quite readily apparent from the geometry of the flanks in Figure 3 by comparison with that of the oil sump in Figure 1.

The damping system shown in Figure 4 - differs from that of Figure 3 only in that instead of the viscous magnetic liquid coat ings 15 and 16 of Figure 3, plastics fila ments 20 and 21 project from the end faces 15 and 16 of the rotor. The plastics fila ments produce a damping of the rotational movement of the rotor 1 similar to that produced by the viscous magnetic liquid.

Differences between the damping produced by the two systems shown in Figures 3 and 4 may arise because the plastics fila ments of Figure 4 may initially have a more clearly defined form than the mag netic liquid quantities in Figure 3, but their shape may change with time. In particular, the filaments may become curved after prolonged operation of the stepping motor.

In contrast to this, the magnetic liquid coatings of Figure 3 may, under the in fluence of the magnetic forces, return into their original shape. If however, any mag netic liquid adheres to the flanks 18 and 19 of the embodiment of Figure 3, the damping effect is not necessarily impaired.

Fundamentally it is immaterial whether the magnetic liquid adheres to the rotating element or to the stationary element. What is important is the effect produced by mag netic liquid between two faces which are displaced relative to one other.

Under some circumstances, it may be advantageous for the damping means to extend in the axial direction of the rotor instead of in the radial direction as shown in all the above embodiments.

WHAT WE CLAIM IS: - 1. A method of damping a stepping motor, the rotor of which rotates from a first stepping position to a second stepping position, wherein the movement of the rotor is damped only during part of its rotation between the two positions.

2. A method of damping a stepping motor according to claim 1, wherein the movement of the rotor is damped in a zone prior to its arrival at a stepping position and is unhindered at the stepping position and in a zone immediately ad jacent thereto.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

motor. The rotor is shown in a first stepping position relative to the stator winding 2.

Two rotating wings 3 and 4 are rigidly secured to the rotor 1, so as to be opposite each other. The wings 3 and 4 are offset by an angle relative to the stator so that in each stepping position one of the two rotating wings 3 and 4 projects completely out of an oil sump 5.

The oil sump 5 is formed by a trough in the interior of a housing 6. The trough is symmetrical about the plane of the rotor axis. Radial cross-sections through the trough have an approximately V-form shape. With this design of trough, the depth of the soil sump increases from zero to a maximum value and then falls to zero again when a rotation path is made in the direction of the arrow 8.

When the rotor 1, is in the position shown in Figure 1, neither of the rotating wings 3 and 4 is in contact with the oil sump 5 and so that rotor movement is initially undamped. Therefore when the rotor 1 starts to rotate towards the second stepping position, it does so with the maximum possible torque. However, as the rotor approaches the second stepping position, the rotating wings 4 dips into the oil sump so that the rotational movement of the rotor is first of all weakly and then more strongly damped. Shortly before the rotor reaches its second stepping position however, the rotating wing moves out of the lowest position of the sump into the shallower portion thereof, so that the damping force is reduced and finally falls to zero in the second stepping position.

Thus, no damping force is present at the second stepping position to hinder the rotor's approach to that position. In the second stepping position, the rotating wing 4 occupies the position of the rotating wing 3 shown in Figure 1. Figure 1 furthermore shows that free, undamped movement takes place within sections 9 and 11 of the entire rotation path, whereas in sections 10 and 12 the rotational movement is damped.

Referring to Figure 3, end faces 13 and 14 of a rotor 1 each have a coating of viscous magnetic liquid. The coatings are denoted by the numerals 15 and 16. A housing 22 encloses a stator winding 2 and has a substantially circular inner recess 17. Flanks 18 and 19 extend into the sections of the rotation path of the rotor 1 to be damped. The flanks 18 and 19 protrude into the inner chamber of the recess far enough to engage with the viscous liquid, but not with the solid body of the rotor 1. The projection of the flanks into the recess increases during part of the rotation path of the viscous liquid and then decreases to zero before the stepping posi tion of the rotor is reached.

With this arrangement, damping of the rotor movement similar to that in the em bodiment shown in Figure 1 is achieved.

However, just before reaching each of the two possible stepping positions, both of the flanks and their associated magnetic liquid coatings interact simultaneously and so their damping forces are combined in their effect. Additionally, there are the damped, sections in Figure 3, as is quite readily apparent from the geometry of the flanks in Figure 3 by comparison with that of the oil sump in Figure 1.

The damping system shown in Figure 4 - differs from that of Figure 3 only in that instead of the viscous magnetic liquid coat ings 15 and 16 of Figure 3, plastics fila ments 20 and 21 project from the end faces

15 and 16 of the rotor. The plastics fila ments produce a damping of the rotational movement of the rotor 1 similar to that produced by the viscous magnetic liquid.

Differences between the damping produced by the two systems shown in Figures 3 and 4 may arise because the plastics fila ments of Figure 4 may initially have a more clearly defined form than the mag netic liquid quantities in Figure 3, but their shape may change with time. In particular, the filaments may become curved after prolonged operation of the stepping motor.

In contrast to this, the magnetic liquid coatings of Figure 3 may, under the in fluence of the magnetic forces, return into their original shape. If however, any mag netic liquid adheres to the flanks 18 and

19 of the embodiment of Figure 3, the damping effect is not necessarily impaired.

Fundamentally it is immaterial whether the magnetic liquid adheres to the rotating element or to the stationary element. What is important is the effect produced by mag netic liquid between two faces which are displaced relative to one other.

Under some circumstances, it may be advantageous for the damping means to extend in the axial direction of the rotor instead of in the radial direction as shown in all the above embodiments.

WHAT WE CLAIM IS: - 1. A method of damping a stepping motor, the rotor of which rotates from a first stepping position to a second stepping position, wherein the movement of the rotor is damped only during part of its rotation between the two positions.
2. A method of damping a stepping motor according to claim 1, wherein the movement of the rotor is damped in a zone prior to its arrival at a stepping position and is unhindered at the stepping position and in a zone immediately ad jacent thereto.
3. The combination of a stepping motor

and a device for damping the stepping motor, said stepping motor having a rotor which rotates from a first stepping position to a second stepping position, said device including: a first damping means attached to the rotor, and a fixed second damping means; wherein the first damping means and the second damping means pass into engagement with each other in a rotational range which is smaller than the rotational path between the two stepping positions.
4. The combination according to claim 3, wherein the first damping means is a rotating wing, and the second damping means is a viscous liquid contained in a trough.
5. The combination according to claim 4, wherein the trough has a rotationallysymmetric cross-section in a plane perpendicular to the rotor axis, and a substantially V-form cross-section in planes extending radially from the rotor axis.
6. The combination according to claim 3, wherein the rotor has stepping positions which are 1800 apart, and in which two rotating wings are attached to the rotor diametrically opposite each other.
7. The combination according to claim 3, wherein the first damping means is a viscous liquid adhering to at least one external face of the rotor, and the second damping means is a stationary flank along which the damping liquid slides before the rotor arrives at the second stepping position.
8. The combination according to claim 7, wherein the viscous liquid is magnetic.
9. The combination according to claim 3, wherein the first damping means is at least one flexible plastics filament.
10. The combination according to any one of claims 3 to 9, wherein the damping means extend in the axial direction of the rotor.
11. The combination of a stepping motor and a device for damping the stepping motor constructed substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2, or Fig. 3, or Fig. 4 of the accompanying drawing.