RU2749581C1 - Apparatus for positioning magnetosensitive elements in external magnetic field - Google Patents

Abstract

FIELD: engineering.SUBSTANCE: invention relates to the area of engineering apparatuses using nuclear magnetic resonance in the magnetic field of the earth, can be used in apparatuses for orientation of magnetically sensitive elements wherein magnetic fields are unacceptable in precision measurements. Substance: the apparatus is made of non-magnetic parts and is comprised of an electric engine the rotor whereof has a common axis with the rotation of the sensor. The sensor is installed on a platform fixed on the axis of the driven gear wheel the driving wheel whereof is fixed on the axis of the electric engine. The electric engine is made in form of two disks, wherein one of the disks is a stator and the other one is a rotor. In the grooves of the stator and the rotor made in form of annular sectors, copper wire windings are located around the axis of rotation. The stator is a support for the platform brake made in form of a ring with a copper wire winding inserted into the annular groove of the stator with an additional copper wire winding around the groove. The ring is pressed to the platform by springs thrust against the bottom of the stator groove.EFFECT: absence of constant magnetic fields, simplicity of design of the engine and fixation of the rotor position with deactivated current powering the apparatus.1 cl, 1 dwg

Description

The invention relates to the field of electrical engineering, in particular, to the field of design of synchronous brushless motors, can be used in devices where magnetic fields are unacceptable for precision measurements, for example, NMR in weak fields. The device allows positioning a magnetically sensitive sensor in space between measurements.

Known industrial NMR device in the earth's magnetic field "Terranova-MRI" from Magritek [1], in which a massive sensor is made in a desktop version. The sensor of the training device "Earth's Field Nuclear Magnetic Resonance" by TeachSpin [2] has a similar design, as well as its version of the sensor with gradient coils "Earth's Field Nuclear Magnetic Resonance Gradient / Field Coil System". In both devices, it is necessary to manually rotate the sensor around the vertical axis until the coil axis is orthogonal with respect to the Earth's magnetic field in order to obtain the maximum signal-to-noise ratio. The claimed invention is able to set the direction of the sensor orthogonal to the earth's magnetic field automatically.

Known Apparatus for orienting a magnetometer US 4600886 A [3], in which the drive for controlling the rotation of the platform with the magnetometer is made in the form of a belt drive to increase the distance between the magnetically sensitive sensor and the device driving the belt drive in order to weaken the influence of the magnetic parts of the drive device on the magnetically sensitive sensor. The claimed invention is free from this drawback, has a more compact design due to the location of the electric drive for rotating the platform in the immediate vicinity of the magnetically sensitive sensor.

Known Non-magnetic servomechanism magnetometer JP 2008116322 A [4], in which a non-magnetic piezoelectric motor driving a platform with a magnetically sensitive sensor in rotation is in close proximity to the sensor. However, piezoelectric motors in the claimed invention will have a number of disadvantages: with a relatively large mass on the shaft (from 2 kg), rather large versions of piezoelectric motors will have to be used, they are sensitive to the ingress of solids, such as sand, high voltages are required to set them in motion (over 100 V) they are relatively expensive due to the required precision in their manufacture. In addition, their main advantage is a very small step and high accuracy in the claimed invention are superfluous.

Known Non-magnetic motor used for servo mechanism of optically pumped magnetometer CN 108418371 A [5], in which a non-magnetic motor driving the platform with a magnetically sensitive sensor in rotation is in close proximity to the sensor. The motor is made of non-magnetic parts and has a similar principle of operation to the motor in the claimed invention, however, it has a complex toroidal design, which does not have the rotor fixation when the motor is powered off.

The technical result of the claimed invention is the absence of permanent magnetic fields, the simplicity of the motor device and the fixation of the rotor position when the current supplying the device is turned off.

The specified technical result is achieved by solving the design of the device. This result is the result of several factors. First, the choice of a synchronous stepper motor circuit, in which the rotating field is created by sequentially supplying electric current to the stator windings, located radially at angles dividing the full rotation of the rotor into equal parts. Secondly, the use of non-ferromagnetic materials in the design of the engine allows precise measurements of magnetic fields when the device is turned off. Third, the mechanical brake holds the rotor when the power is off.

The essence of the claimed invention is illustrated in FIG. 1, which shows a diagram of the device and the arrangement of electrical windings, while FIG. 1 a) shows a front section of the device and in Fig. 1 b) shows a top view of the stator and rotor windings of the motor and the platform brake.

FIG. 1 a) shows a device of the claimed invention made of non-magnetic parts, consisting of a horizontal platform (1) on which an NMR sensor or other magnetically sensitive element is located. The platform is fixed on the axle of the driven gear wheel. The reducer (2) consists of three wheels (gears) (3). The driven wheel is made in the form of a gear with internal gearing. Thus, the axes of the driving and driven wheels coincide, but have different speeds. The intermediate wheel is used to connect the driven and driving wheels. The drive wheel of the reducer is fixed on the axis of the electric motor, made in the form of two disks: the rotor (4) and the stator (5). In both discs, grooves in the form of annular sectors around the axis of rotation are milled or otherwise made. The grooves contain windings made of copper wire (6). The stator is also a support for the platform brake, which is made in the form of a ring (7) with a winding of copper wire (10) inserted into the annular groove of the stator. The stator also has an additional copper wire winding, surrounded by an annular groove (10). When voltage is applied to the brake winding and the winding surrounded by the ring groove of the brake, the magnetic fields of the windings interact so that they are attracted to each other and the ring (7) is pulled into the groove, overcoming the resistance of the spring (9), and frees the platform (1) for turning. At the point of contact of the ring with the platform, a friction coating (11) is glued or applied. When the current in the brake windings is turned off, the spring presses the brake ring (7) to the platform (1), which prevents it from turning.

FIG. 1 b) the top view shows the location of the electrical windings. The rotor winding, which consists of six circular sectors, shown in dark gray, is supplied with direct current. The rotor windings are connected in such a way that alternating magnetic poles are formed around the axis of rotation. The stator windings are two layers of windings, similar to those on the rotor, but the layers are shifted by an angle of half of one winding, the second layer in Fig. 1 b) is shown as translucent. Thus, when alternating the supply of current to two layers of the stator windings and changing the direction of the current, a stepwise rotation of the magnetic field is created, which, interacting with the constant magnetic fields of the rotor, rotates the latter.

Automatic orientation is carried out by an algorithm that analyzes the NMR signal or a signal from another magnetically sensitive element installed on the platform and sends a command to the engine to turn in one direction or another until the maximum signal-to-noise ratio of the NMR sensor or the required output value of the set magnetically sensitive element.

The claimed invention operates as follows. The voltage corresponding to the current position of the rotor is applied to the windings (6) of the stator (5) and rotor (4)

(4), then voltage is applied to the windings (10) of the brake, while the ring (7), overcoming the force of the spring made of non-magnetic metal (9), releases the platform (1), then the current in the stator windings (5) changes so that turn the rotor (4) one or several necessary successive steps, after which the current in the brake windings (10) is turned off and the rotor position is fixed, and the current in all windings (6) is turned off. In this case, the motor is de-energized and the necessary magnetically sensitive measurements can be carried out.

The claimed invention was tested in the laboratory of St. Petersburg State University (at the Faculty of Physics at the Department of Nuclear Physics Research Methods). The operability of the claimed invention and the achievement of the specified technical result were confirmed.

Below is a specific example of the validation results.

A working model of a drive with six coils on a stator made in the form of a disc with a diameter of 100 mm and a rotor in the form of the same disc with 12 coils (all coils are wound with a wire with a diameter of 0.4 mm, each have 200 turns of wire) at a voltage of 12 V to the motor and the gear ratio of the reducer 120 confidently, without missing steps, turned the platform with a sensor with a total weight of 2.5 kg, the brake fixed the platform, withstanding a force of 750 g to rotate the platform in the horizontal plane at the end of the lever arm 200 mm connected to the center of the turntable. The engine was controlled by a microcontroller according to a special algorithm, which analyzed the NMR signal from the sensor and sent commands to the engine in order to find such a horizontal angle of the sensor with respect to the Earth's magnetic field, at which the maximum amplitude of the NMR signal would be recorded. Thus, the sensor was oriented perpendicular to the Earth's magnetic field, which is necessary for the maximum signal-to-noise ratio in NMR experiments in the Earth's field. This process took about 20 registration-rotation cycles, which was about 2 minutes of time.

List of information sources

1.http: //www.magritek.com/wp-content/uploads/2013/12/Magritek-MRI-2011-web.pdf

2.https://www.teachspin.com/earths-field-nmr

3. Apparatus for orienting a magnetometer US 4600886 А

4. Non-magnetic servomechanism magnetometer JP 2008116322 A

5. Non-magnetic motor used for servo mechanism of optically pumped magnetometer CN 108418371 A

Claims (1)

A device for orientation of magnetically sensitive elements in an external magnetic field, made of non-magnetic parts, containing an electric motor, the rotor of which has an axis in common with the rotation of the sensor, characterized in that the sensor is mounted on a platform that is fixed on the axis of the driven gear wheel, the driving wheel of which is fixed on the axis of an electric motor made in the form of two disks, one of which is a stator, and the second is a rotor, in the grooves of the stator and rotor, made in the form of annular sectors, windings made of copper wire are located around the axis of rotation, the stator is a support for the platform brake, which is made in the form of a ring with a copper wire winding inserted into the annular groove of the stator, having an additional copper wire winding around the groove, the ring is pressed against the platform by springs abutting the bottom of the stator groove.

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