GB1587772A

GB1587772A - Polarized electromagnetic drive

Info

Publication number: GB1587772A
Application number: GB2991/78A
Authority: GB
Original assignee: ELMEG Elektro Mechanik GmbH
Current assignee: ELMEG Elektro Mechanik GmbH
Priority date: 1977-01-29
Filing date: 1978-01-25
Publication date: 1981-04-08
Also published as: IT7819750A0; IT1091825B; JPS5396410A; FR2379188A1; DE2703788A1; DE2703788C3; DE2703788B2; FR2379188B1

Description

(54) A POLARIZED ELECTROMAGNETIC DRIVE (71) We, ELEKTRO-MECHANIK G.m.b.H., of Wendener-Hutte, Kreis Olpe, Federal Republic of Germany, a German body corporate, 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 invention relates to a polarized electromagnetic drive preferably for actuating a servo rotary valve and comprising two permanent magnets, field iron parts partially encircling the permanent magnets, an armature with the drive shaft and control coils.

By a polarized electromagnetic drive for the above-mentioned purpose is meant an electromechanical transducer, the object of which lies in transducing electrical input signals in the form of electrical currents into proportional mechanical output magnitudes, such as torque, force, rotary angle or path. The polarized electromagnetic drives known as control motors also called torque motors, serve among other things to control servo valves. In general they only fulfil their task over a small rotary angle or path, for example in the rotary angle range up to approximately 2 degrees i.e. in the range of proportional relationship between the output magnitude and the input magnitude.

With a rotary angle larger than approximately 2 degrees, the output magnitude changes exponentially as related to the input magnitude and this is inherent in the system, so that a proportional relationship between the input and output magnitude no longer exists in this range and therefore this range, which makes up more than half of the geometrically possible region, cannot normally be utilized. Increasing the rotary angle range beyond approximately 2 degrees and maintenance proportional relationship at the same time between the input and output magnitudes and maintenance of the same force or torque, can only be achieved in the known electromagnetic drive devices by increasing the total volume of the device.

The invention therefore seeks to create an electromagnetic drive device which has a considerable and relatively large rotary angle range with the same torque and the small overall size and has a proportional relationship between the input and output magnitudes.

According to the invention, there is provided a polarized electromagnetic drive comprising two permanent magnets, field iron parts partially encircling the permanent magnets, an armature arranged on a drive shaft for limited angular movement therewith and control coils, the field iron parts extending between the permanent magnets and the armature in the region of poles of the armature such as to provide large and small air gaps between the field iron parts and the armature, the arrangement being such that the total deflecting force acting on the armature and formed by the sum of the individual components of the large and small air gaps has a greater linearity range with respect to the control circuit than the individual components.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a cross-section of the electromagnetic drive device; Figure 2 shows a cross-section of the spring centring associated with the drive device, and Figure 3 shows a diagram of the deflection torque or rotary angle over the control current.

In Figure 1 the permanent magnets are designated 1 these being partially encircled by two field iron parts 2. The armature 4 is located on the drive shaft 3 which is provided with damping windings 5. The field iron parts 2 are provided with projections 13 between armature 4 and permanent magnets 1, radially opposite the armature poles so that small air gaps 12 as well as large gaps 11 are present between the armature 4 and the field iron parts 2. Control coils 6 are arranged so as to encircle the armature 4 in a transverse direction. The spring centring shown in accordance with Figure 2 comprises a lever arm 7, springs 8, spring accommodating parts 9 and a zero point setting screw 10.

The mode of operation of the drive device in accordance with the invention is as follows: The two permanent magnets 1 bring about a magnetic flux MI in the large air gaps 11 and a magnetic flux M2 in the small air gaps 12. If an electrical current flows through the control coils 6 then magnetic circulation occurs which brings about a magnetic control flux , in the armature 4.

The magnetic control flux , is divided up into the large air gaps 11 and the small air gaps 12 in accordance with their magnetic resistances and is superimposed, in the large air gaps 11, on the magnetic flux M1 and, in the small air gaps 12, on the magnetic flux ( > M2 A deflection force on the armature 4 is formed as a result of these superimpositions of the magnetic fluxes and thus a deflection torque is also formed which sets the armature 4 into rotary motion until the countertorque applied by the spring centring by the lever arm 7 and the springs 8 is of the same magnitude i.e. of opposite direction to the deflection torque and as a result stops the armature 4.The rotary angle of the armature 4 is proportional to the magnitude and direction of the current flowing through the control coils 6 inside the region determined by the geometry of the air gaps 11 and 12.

In the large air gaps 11 the deflection force action on the armature 4 is based on the difference between the attractive forces of the parts lying opposite each other and penetrated by the superimposed magnetic fluxes, which attractive forces act in a rotary direction and in a counter rotary direction, said parts being the field iron parts 2 and the armature poles 14. In the small air gaps 12 the deflection force action on the armature 4 is based on the force action of two magnetic fields perpendicular to each other, in the present case, the magnetic fluxes 4)M7 flowing through the small air gaps 12 and flowing transversely in the armature poles 14 and the control flux (t)s which is dependent on the current direction and in perpendicular manner meets the latter.

The linear relationship between the control current flowing through the control coils 6 and the deflection force on the armature 4, is based on adding the force components (acting in the same direction) of the large and small air gaps 11 and 12 so that the force components of the large and small air gaps 11 and 12 are in a linear relationship to the control current flowing through the control coils 6 in the small deflection range.With larger deflections, however, the force component of the large air gaps 11 increases exponentially because the armature poles 14 approach the field iron parts 2 in a rotary direction and thus the magnetic resistances of the large air gaps 11 decrease in a rotary direction and increase counter to the rotary direction, whereby the superimposed magnetic fluxes increase in the large air gaps 11 in a rotary direction, and armature poles 14 and field iron parts 2 are attracted more strongly accordingly. The force action decreases, however, in the large air gaps 11 in a counter direction to rotation, by increasing the magnetic resistances and thus reducing the superimposed magnetic fluxes and thus increasing the steepness of the exponential rise in force.In contrast, however, the force component of the small air gaps 12 decreases with fairly large deviations (Figure 3), because the effective magnetic resistances of the small air gaps 12 increase owing to saturation phenomena and thus the magnetic fluxes superimposed and effective in the small air gaps 12 decreases. Owing to common force effects of the large and small air gaps 11 and 12 there is a substantially larger linear deflection range of the armature 4 than that of the individual force components (Figure 3).

The moment of inertia of the armature 4 forms a spring-mass system together with the spring centring which is damped sufficiently by the damping turns 5 located on the armature 4. A similar damping effect is achieved, if the damping turns 5 are arranged in the coil area of the field iron parts 2, or if the control coils 6 themselves are directly short-circuited or are shortcircuited via an impedance network. With the aid of the zero point setting screw 10, the zero point of the drive device can be changed.

With the aid of sheets 15, which are arranged over the permanent magnets 1 and thus form a small magnetic shunt, the steepness of the drive device, i.e. the dependence of the armature rotary angle on the control current, can be changed.

WHAT WE CLAIM IS: 1. A polarized electromagnetic drive comprising two permanent magnets, field iron parts partially encircling the permanent magnets, an armature arranged on a drive shaft for limited angular movement therewith and control coils, the field iron parts extending between the permanent magnets and the armature in the region of poles of the armature such as to provide large and small air gaps between the field iron parts

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. iron parts 2 are provided with projections 13 between armature 4 and permanent magnets 1, radially opposite the armature poles so that small air gaps 12 as well as large gaps 11 are present between the armature 4 and the field iron parts 2. Control coils 6 are arranged so as to encircle the armature 4 in a transverse direction. The spring centring shown in accordance with Figure 2 comprises a lever arm 7, springs 8, spring accommodating parts 9 and a zero point setting screw 10. The mode of operation of the drive device in accordance with the invention is as follows: The two permanent magnets 1 bring about a magnetic flux MI in the large air gaps 11 and a magnetic flux M2 in the small air gaps 12. If an electrical current flows through the control coils 6 then magnetic circulation occurs which brings about a magnetic control flux , in the armature 4. The magnetic control flux , is divided up into the large air gaps 11 and the small air gaps 12 in accordance with their magnetic resistances and is superimposed, in the large air gaps 11, on the magnetic flux M1 and, in the small air gaps 12, on the magnetic flux ( > M2 A deflection force on the armature 4 is formed as a result of these superimpositions of the magnetic fluxes and thus a deflection torque is also formed which sets the armature 4 into rotary motion until the countertorque applied by the spring centring by the lever arm 7 and the springs 8 is of the same magnitude i.e. of opposite direction to the deflection torque and as a result stops the armature 4.The rotary angle of the armature 4 is proportional to the magnitude and direction of the current flowing through the control coils 6 inside the region determined by the geometry of the air gaps 11 and 12. In the large air gaps 11 the deflection force action on the armature 4 is based on the difference between the attractive forces of the parts lying opposite each other and penetrated by the superimposed magnetic fluxes, which attractive forces act in a rotary direction and in a counter rotary direction, said parts being the field iron parts 2 and the armature poles 14. In the small air gaps 12 the deflection force action on the armature 4 is based on the force action of two magnetic fields perpendicular to each other, in the present case, the magnetic fluxes 4)M7 flowing through the small air gaps 12 and flowing transversely in the armature poles 14 and the control flux (t)s which is dependent on the current direction and in perpendicular manner meets the latter. The linear relationship between the control current flowing through the control coils 6 and the deflection force on the armature 4, is based on adding the force components (acting in the same direction) of the large and small air gaps 11 and 12 so that the force components of the large and small air gaps 11 and 12 are in a linear relationship to the control current flowing through the control coils 6 in the small deflection range.With larger deflections, however, the force component of the large air gaps 11 increases exponentially because the armature poles 14 approach the field iron parts 2 in a rotary direction and thus the magnetic resistances of the large air gaps 11 decrease in a rotary direction and increase counter to the rotary direction, whereby the superimposed magnetic fluxes increase in the large air gaps 11 in a rotary direction, and armature poles 14 and field iron parts 2 are attracted more strongly accordingly. The force action decreases, however, in the large air gaps 11 in a counter direction to rotation, by increasing the magnetic resistances and thus reducing the superimposed magnetic fluxes and thus increasing the steepness of the exponential rise in force.In contrast, however, the force component of the small air gaps 12 decreases with fairly large deviations (Figure 3), because the effective magnetic resistances of the small air gaps 12 increase owing to saturation phenomena and thus the magnetic fluxes superimposed and effective in the small air gaps 12 decreases. Owing to common force effects of the large and small air gaps 11 and 12 there is a substantially larger linear deflection range of the armature 4 than that of the individual force components (Figure 3). The moment of inertia of the armature 4 forms a spring-mass system together with the spring centring which is damped sufficiently by the damping turns 5 located on the armature 4. A similar damping effect is achieved, if the damping turns 5 are arranged in the coil area of the field iron parts 2, or if the control coils 6 themselves are directly short-circuited or are shortcircuited via an impedance network. With the aid of the zero point setting screw 10, the zero point of the drive device can be changed. With the aid of sheets 15, which are arranged over the permanent magnets 1 and thus form a small magnetic shunt, the steepness of the drive device, i.e. the dependence of the armature rotary angle on the control current, can be changed. WHAT WE CLAIM IS:

1. A polarized electromagnetic drive comprising two permanent magnets, field iron parts partially encircling the permanent magnets, an armature arranged on a drive shaft for limited angular movement therewith and control coils, the field iron parts extending between the permanent magnets and the armature in the region of poles of the armature such as to provide large and small air gaps between the field iron parts

and the armature, the arrangement being such that the total deflecting force acting on the armature and formed by the sum of the individual components of the large and small air gaps has a greater linearity range with respect to the control circuit than the individual components.

2. A polarized electromagnetic drive according to Claim 1, wherein, in order to damp the drive device, damping turns are arranged on the armature.

3. A polarized electromagnetic drive according to Claim 1, wherein, in order to damp the drive device, damping turns are arranged in the coil area of the field iron parts.

4. A polarized electromagnetic drive according to Claim 1, wherein in order to damp the drive device, the control coils are short-circuited directly or via an impedance network.

5. A polarized electromagnetic drive according to Claim 1, 2, 3, or 4, wherein spring centring, comprising springs and lever arm is provided for producing a countertorque.

6. A polarized electromagnetic drive according to Claim 5, wherein the spring centring is provided with a screw for setting the zero point.

7. A polarized electromagnetic drive according to any one of claims 1 to 6 wherein the dependence of the armature rotary angle on the control current can be varied by metal sheets arranged over the magnets.

8. A polarized electromagnetic drive substantially as described herein with reference to the drawings.