Drive control mechanism

Abstract

A drive control mechanism 100 comprising: a stator assembly 4, the stator assembly comprising windings 5; a rotor 11, the rotor comprising a friction plate 15; and ferromagnetic material; the rotor be

Description

CROSS REFERENCE TO RELATED APPLICATIONS This represents the first application directed towards the subject-matter. FIELD This disclosure relates to drive control mechanisms for rotating shafts. BACKGROUND Rotating drive shafts are used in numerous technologies. It is desirable to produce simpler, more compact mechanisms for controlling the rotation of a driveshaft. SUMMARY The present disclosure provides a drive control mechanism as set out in claim 1. Optional features are included in the dependent claims. According to a first aspect there is provided a drive control mechanism comprising: a stator assembly, the stator assembly comprising a plurality of stator windings; a rotor, the rotor comprising: a friction plate; and ferromagnetic material; the rotor being rotatably secured to a drive shaft such that the friction plate is located in a plane perpendicular to the rotational axis of the drive shaft so as to form part of an electromagnetic clutch system; the electromagnetic clutch system further comprising a clutch plate connected to the drive shaft, and an armature, the armature comprising ferromagnetic material and being connected to the clutch plate and located opposite to, and in a plane parallel to, the friction plate of the rotor, the armature being biased away from the friction plate so as to leave a gap between the armature and friction plate; wherein the stator windings are located proximal to the armature and the rotor such that passing an electric current through the stator windings creates an electromagnetic field that: activates the electromagnetic clutch by pulling the armature of the electromagnetic clutch into contact with the friction plate of the rotor so as to create a friction lock between the armature and the friction plate; and controls the rotational position of the drive shaft; such that the stator windings can only control rotation the drive shaft when the electromagnetic clutch is activated. The rotor of the drive control mechanism may comprise a plurality of poles oriented parallel to the rotational axis of the drive shaft, the poles comprising ferromagnetic material, and stator windings which are oriented such that, when a current is passed through the stator windings, the stator assembly creates radial magnetic fields, having first magnetic poles facing away from the drive shaft, and second magnetic poles facing towards the drive shaft, which can act upon the plurality of poles of the rotor so as to rotate the rotor. The friction plate of the drive control mechanism may comprise a plurality of magnetic poles, with the stator windings being oriented such that, when a current is passed through the stator windings, the stator assembly creates axial magnetic fields, having first magnetic poles facing away from towards the friction plate, and second magnetic poles facing the friction plate, such that the stator windings can control rotation of the rotor via rotation of the friction plate. The armature of the drive control mechanism may comprise a plurality of magnetic poles, with the stator windings being oriented such that, when a current is passed through the stator windings, the stator assembly creates an axial magnetic field, having first magnetic poles facing towards the armature, and second magnetic poles facing away from the armature, such that the stator windings can control rotation of the rotor via rotation of the armature. The drive control mechanism may further comprise a drive shaft position indicator system comprising an indicator sensor and a shaft indicator, the shaft indicator being connected to the drive shaft, and the indicator sensor being positioned proximal the shaft indicator, such that the indicator sensor can detect the rotation of the drive shaft. The position indicator system may comprise a Hall effect sensor. The stator assembly of the drive control mechanism may comprise a cooling jacket, the cooling jacket being located proximal to the stator windings and capable of conveying a fluid medium so as to be capable of absorbing, and transferring heat energy away from, the stator windings. The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and / or combined with any other feature described herein. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments will now be described by way of example only with reference to the accompanying drawings, in which: FIG. 1 shows a sectional schematic view of an example drive control mechanism; FIG. 2 shows a sectional schematic view of the example drive shaft of FIG. 1 in its activated configuration; FIG. 3 shows a sectional schematic view of another example drive control mechanism; and FIG. 4 shows a sectional schematic view of the example drive control mechanism of FIG. 3 in its activated configuration. DETAILED DESCRIPTION FIG. 1 shows a sectional schematic view of an example drive control mechanism 100. The drive control mechanism 100 is connected to a drive shaft 1. The drive control mechanism 100 includes a rotor 11. At least some of the rotor is made using a ferromagnetic material, so as to exhibit magnetic properties when positioned within an electromagnetic field. In the example drive control mechanism of FIG, 1, which uses radial electromagnetic fields, the rotor has four poles 18 (i.e. with two additional poles out of the plain of FIG. 1), formed by sections of the rotor 11 extending parallel to the drive shaft. The rotor is rotatably secured to the drive shaft 1, which is to say that the position of the rotor is fixed with respect to the drive shaft, but the rotor can rotate freely around the drive shaft. In the example drive control mechanism of FIG. 1, an optional position indicator core 3 is shown attached to one end of the drive shaft. In the example drive control mechanism of FIG. 1, the drive control mechanism is fixed in position with respect to the drive shaft by means of several bearings 7, 8, 9, 19 which allow for accurate location and smooth rotational movement of the rotor 11 around the drive shaft 1. Specifically, upper 7 and lower 19 thrust bearings located between the rotor 11 and the stator assembly 4 prevent the rotor from sliding axially along the drive shaft, whilst upper rotor centralising bearings 8 and lower rotor centralising bearings 9 keep the rotational axis of the rotor 11 aligned with the rotational axis of the drive shaft 1. The drive control mechanism also includes an electromagnetic clutch 20 (indicated by dashed-line box in the FIG.s), which comprises a friction plate 15 (part of the rotor 11) and a clutch plate 14 which is connected to the drive shaft. As illustrated in FIG. 1, the friction plate 15 is located at the end of the rotor 11 furthest from the position indicator core 3, in a plane perpendicular to the rotational axis of the drive shaft, so as to be parallel with, and facing towards, the clutch plate. Connected to the clutch plate 14 via at least a clutch spring 16 (see FIG. 2) is an armature 21, which is at least partially constructed using a ferromagnetic material, so as to exhibit magnetic properties when positioned within an electromagnetic field. The armature 21 is located opposite the friction plate 15 of the rotor 11, and oriented parallel to the friction plate 15 of the rotor 11. In the absence of an external force other than the clutch spring 16 acting on the armature 21, the clutch spring will hold the armature 21 at a distance from the friction plate 15 so as to maintain a gap between the friction plate and the armature, as shown in FIG. 1. The skilled person will appreciate that the clutch spring may take the form of any suitable resilient element designed to resist extension, such as one or more plate springs, coil springs, or flat springs. The drive control mechanism further comprises a stator assembly 4, comprising a plurality of stator windings 5. The stator windings are arranged around the rotor 11 - commonly six or eight sets of stator windings 5, although the skilled person will appreciate the exact number can be varied depending on the demands of the system. In the example drive control mechanism of FIG. 1, the stator assembly is configured to interact with the rotor 11 in the style of a radial flux motor. As such, the stator assembly 4 has a hollow interior, and is sized so that the rotor 11 can be inserted through the hollow interior of the stator assembly. In the example drive control mechanism of FIG. 1, the stator assembly 4 is positioned such that the stator windings 5 are proximal to the poles 18 of the rotor 11. The stator windings are arranged to generate radial electromagnetic fields, which is to say that the magnetic axes of the electromagnetic fields generated by the stator windings are aligned with lines radial to the rotational axis of the rotor. This means that when a current is passed through the stator windings, the stator assembly creates radial magnetic fields, having first magnetic poles facing away from the drive shaft, and second magnetic poles facing towards the drive shaft. The relative locations of the rotor 11 and stator windings 5 are such that when a sufficient electric current is passed through the stator windings 5, the radially extending electromagnetic fields generated by the stator windings 5 envelop the poles 18 of the rotor 11, and can be used to produce a motive force acting upon the poles of the rotor 11, as is known for radial flux motors. The stator assembly, specifically the stator windings, are located in a position proximal to both the rotor 11 and the armature 21, so that the electromagnetic fields produced by the stator windings can effectively influence the movement and position of the rotor via the generation and alteration of electromagnetic fields. In the example drive control mechanism of FIG. 1, as the poles 18 of the rotor 11 comprise ferromagnetic material, the electromagnetic fields can act directly upon the poles 18 of the rotor to control the movement and position of the rotor. Having the stator windings 5 within proximity of the armature 21 of the electromagnetic clutch 20 means that, when an electric current is passed through the stator windings 5, the electromagnetic fields which are generated also envelop the armature 21. The armature, being at least partially constructed from a ferromagnetic material, will be attracted towards the stator windings 5, and so will pull against the resistive force of the clutch spring 16, until the armature 21 moves into contact with the friction plate 15 of the rotor 11. The strength of the force of the electromagnetic fields upon the armature is such that it creates a friction lock between the armature 21 and the friction plate 15. Both the armature 21 and the friction plate 15 may incorporate friction-enhancing features, such as roughened surfaces, or interlocking surface features such as teeth and grooves, in order to increase the strength of the friction lock. In FIG. 1, the drive control mechanism 100 is shown in its deactivated state, i.e. where the electromagnetic clutch 20 has been disengaged, such that the clutch spring 16 has pulled the armature 21 out of contact with the friction plate 15 of the rotor 11. As such, the position of the rotor 11 no longer has any effect on the position of the drive shaft 1, as the connection (the friction lock between the armature 21 and the friction plate 15) that links the rotational position of the rotor to the rotational position of the drive shaft has been broken, and the drive shaft will be able to rotate freely of its own accord. FIG. 2 shows a sectional schematic view of the example drive shaft of FIG. 1 in its activated configuration, meaning that an electric current is being passed through the stator windings 5 and an electromagnetic field has been established which envelopes the armature 21, such that the armature has overcome the resistive force of the clutch spring 16, and been pulled into contact with the friction plate 15 to form a friction lock. As the armature is connected to the clutch plate 14, which in turn is connected to the drive shaft 1, once the friction plate of the rotor 11 establishes a friction lock with the armature 21, rotation of the rotor will cause rotation of the drive shaft. Referring to FIG. 1 and FIG. 2, the drive control mechanism operates as follows: starting from the deactivated state shown in FIG. 1, the drive shaft will be freely rotatable. To control and change the rotational position of the drive shaft, an electric current is passed through the stator windings 5 to create electromagnetic fields to activate the electromagnetic clutch 20. The electromagnetic fields pull on the armature 21 of the electromagnetic clutch, bringing the armature towards the friction plate 15 until it engages with the friction plate, creating a friction lock between the armature and the friction plate, as shown in FIG. 2. The flow of current through the stator windings will determine the electromagnetic fields generated by the stator windings, which in turn will determine the rotational force exerted by the electromagnetic fields on the poles 18 of the rotor 11, as is known for radial flux motors. With the electromagnetic clutch engaged (which is to say, with the friction lock between the armature and the friction plate established), rotation of the rotor will cause rotation of the drive shaft. Therefore, by controlling the flow of current through the plurality of stator windings, both the engagement of the electromagnetic clutch, and the rotation of the drive shaft, can be controlled. FIG. 3 shows a sectional schematic view of another example drive control mechanism 100. The drive control mechanism of FIG. 3 shares many design features with the example drive control mechanism of FIG. 1 and FIG. 2. The drive control mechanism of FIG. 3 has a rotor 11 which is rotatably secured to a drive shaft 1, which is to say that the position of the rotor is fixed with respect to the drive shaft, but the rotor can rotate freely around the drive shaft. In the example drive control mechanism of FIG. 3, a position indicator core 3 is attached to one end of the drive shaft. In the example drive control mechanism of FIG. 3, the drive control mechanism is fixed in position with respect to the drive shaft by means of bearings 8 and 19, which allow for accurate location and smooth movement of the rotor 11 around the drive shaft 1. Specifically, the lower thrust bearings 19 located between the rotor 11 and the interior surface of the stator assembly 4 prevent the rotor from sliding axially along the drive shaft, whilst upper rotor centralising bearings 8 keep the rotational axis of the rotor 11 aligned with the rotational axis of the drive shaft 1. The example drive control mechanism of FIG. 3 also includes an electromagnetic clutch 20, which comprises a friction plate 15 (part of the rotor 11) and a clutch plate 14 which is connected to the drive shaft 1. The friction plate 15 is located at the end of the rotor 11 furthest from the position indicator core 3, in a plane perpendicular to the rotational axis of the drive shaft, as illustrated in FIG. 3, so as to be parallel with, and facing towards, the clutch plate. As part of the rotor 11, the friction plate 15 is made using a ferromagnetic material, so as to exhibit magnetic properties when positioned within a magnetic field. Specifically, the friction plate in the example drive control mechanism of FIG. 3 (and FIG. 4) comprises a plurality of permanent magnets so as to provide the friction plate with a number of magnetic poles. Connected to the clutch plate 14 via a clutch spring 16 (see FIG. 4) is an armature 21, which is also made using a ferromagnetic material so as to exhibit magnetic properties when positioned within a magnetic field. The armature 21 is located opposite the friction plate 15 of the rotor 11, and oriented parallel to the friction plate 15 of the rotor 11. In the absence of an external force other than the clutch spring 16 acting on the armature 21, the clutch spring will hold the armature 21 at a distance from the friction plate 15 so as to maintain a gap between the friction plate and the armature, as shown in FIG. 3. The skilled person will appreciate that the clutch spring may take the form of any suitable resilient element designed to resist extension, such as one or more plate springs, coil springs, or flat springs. The drive control mechanism further comprises a stator assembly 4, comprising a plurality of stator windings 5. The stator assembly 4 has a hollow interior, and is sized so that the rotor 11 can be inserted through the hollow interior of the stator assembly. In the example drive control mechanism of FIG. 3, the stator assembly is configured in the style of an axial flux motor, which is to say that the stator windings are oriented such that, when an electric current is passed through them, the electromagnetic fields generated by the stator windings will have magnetic axes aligned with lines parallel to the rotational axis of the rotor. In other words, when a current is passed through the stator windings of the example drive control mechanism 100 of FIG. 3, the stator assembly creates axial magnetic fields having first magnetic poles facing towards the friction plate, and second magnetic poles facing away from the friction plate. The stator windings are arranged such that the electromagnetic fields generated by the stator windings intersect with the friction plate 15 and armature 21 of the electromagnetic clutch 20. Specifically, the stator windings 5 are located close enough to the friction plate 15, and armature 21, such that when a sufficient electric current is passed through the stator windings 5, axially extending electromagnetic fields are generated by the stator windings 5 which envelop the friction plate 15 and armature 21, and which can be used to both draw the armature into contact with the friction plate 15, and to produce motive force acting upon the magnetic poles of the friction plate, as is known for axial flux motors. The stator assembly, and particularly the stator windings, are located in a position proximal to the friction plate, from where they can effectively influence the movement and position of the poles of the friction plate via the generation and alteration of electromagnetic fields. The location of the stator windings 5 is such that they are also close enough to the armature 21 of the electromagnetic clutch 20, such that, when an electric current is passed through the stator windings 5, the electromagnetic fields which are generated also envelop the armature 21. The armature, being at least partially constructed from a ferromagnetic material, will be attracted towards the stator windings 5, and so will pull against the resistive force of the clutch spring 16, until the armature moves into contact with the friction plate 15 of the rotor 11. The strength of the force upon the armature is such that it creates a friction lock between the armature 21 and the friction plate 15. Both the armature 21 and the friction plate 15 may incorporate friction-enhancing features, such as roughened surfaces, or interlocking surface features such as teeth and grooves, in order to increase the strength of the friction lock. In FIG. 3, the drive control mechanism 100 is shown in its deactivated state, i.e. where the electromagnetic clutch 20 has been disengaged, such that the clutch spring 16 has pulled the armature 21 out of contact with the friction plate 15 of the rotor 11. As such, the position of the rotor 11 no longer has any effect on the position of the drive shaft 1, as the connection that links the rotational position of the rotor to the rotational position of the drive shaft (i.e. the friction lock between the armature 21 and the friction plate 15) has been broken, and as a result the drive shaft will be able to rotate freely. FIG. 4 shows a sectional schematic view of the example drive control mechanism of FIG. 3 in its activated configuration, meaning that an electric current is being passed through the stator windings 5 and electromagnetic fields have been established, such that the armature 21 has overcome the resistive force of the clutch spring 16, and been pulled into contact with the friction plate 15 to form a friction lock. As the armature is connected to the clutch plate 14, which in turn is connected to the drive shaft 1, once the friction plate establishes a friction lock with the armature 21 of the rotor 11, rotation of the rotor will cause rotation of the drive shaft. The example drive control mechanism of FIG. 3 and FIG. 4 operates in the same fashion as that of the example drive control mechanism of FIG. 1 and FIG. 2. Starting from the deactivated state shown in FIG. 3, the drive shaft will be freely rotatable due to the electromagnetic clutch being disengaged. To change the rotational position of the drive shaft, an electric current is passed through the stator windings to create electromagnetic fields, which activate the electromagnetic clutch. The electromagnetic fields generated by the stator windings pull on the armature of the electromagnetic clutch, bringing the armature towards the friction plate until the armature engages with the friction plate, creating a friction lock between the armature and the friction plate, as shown in FIG. 4. As with an axial motor, the flow of current through the stator windings will determine the electromagnetic fields generated by the stator windings, which in turn will determine the rotational force exerted on the poles 18 of the rotor 11 (i.e. the permanent magnets on the friction plate in the example drive control mechanism of FIG. 3 and FIG. 4). With the electromagnetic clutch engaged (which is to say, with the friction lock between the armature and the friction plate established), rotation of the rotor will cause rotation of the drive shaft. Therefore, as with the example drive control mechanism of FIG. 1 and FIG. 2, by controlling the flow of current through the stator windings, engagement of the electromagnetic clutch, and the rotation of the drive shaft, can be controlled. The skilled person will appreciate that an alternative axial flux motor configuration is possible, where, instead of the friction plate being fitted with permanent magnets, it is the armature that is fitted with permanent magnets, so that the armature has magnetic poles. The configuration is otherwise the same as that described above for the example drive control mechanism of FIG. 3 and FIG. 4. In this alternative axial flux motor configuration, passing a current through the stator windings 5 will generate axial electromagnetic fields that pass through the ferromagnetic material of the friction plate to reach the magnetic poles of the armature, both attracting the armature towards the friction plate so as to form a friction lock with the friction plate (and thus engage the electromagnetic clutch), and allowing the rotational position of the armature, and thus the rotor it is connected to via the friction plate, to be controlled. Being able to both activate the electromagnetic clutch 20 and control the rotational position of the rotor 11 using a single set of stator windings has advantages over prior art drive control mechanism designs. For example, the parts count for the drive control mechanism is reduced compared to alternative designs having separate mechanisms to control the rotational position of the rotor and the engagement or release mechanism of the drive system, potentially leading to cost savings and improved reliability. Furthermore, the mass and volume may be reduced compared to separate motor and clutch devices. In operation, the stator windings 5 will heat up as a result of the electric current being passed through them. In order to prevent the heat generated by the stator windings leading to damage and performance degradation, a cooling jacket 6 can be located within the stator assembly 4, proximal to the stator windings 5. The cooling jacket may be arranged so as to encircle the stator windings 5, such that the stator windings are located between the cooling jacket 6 and the rotor 11, as shown in FIG. 1, FIG. 2, FIG. 3, and FIG. 4. The cooling jacket may take the form of a fluid jacket or fluid coils through which a fluid medium can be passed, the fluid medium being able to absorb heat energy from the stator windings 5 before transferring the heat energy away from the drive shaft to a separate location where the absorbed heat energy can be removed from the fluid medium. The fluid medium can then be recirculated to the cooling jacket to repeat the process, and thus help keep the stator windings within a tolerable temperature range for long-term functionality. As only a single set of stator windings is required, the amount and complexity of cooling needed to maintain the drive control mechanism within a functionally sustainable temperature range is reduced, compared with prior art drive control mechanism designs. In the example drive control mechanisms of FIG.1, FIG. 2, FIG. 3, and FIG. 4, an optional driveshaft position indicator 2 is shown connected to the stator assembly 4, proximal to the location of the optional position indicator core 3 located at one end of the drive shaft 1. The purpose of the driveshaft position indicator 2 and the position indicator core 3 is to detect the rotational movement of the drive shaft, such that, when the drive shaft is rotated, the driveshaft position indicator 2 can detect the rotation of the position indicator core 3, and therefore track the rotation and rotational position of the drive shaft. The driveshaft position indicator 2 may comprise a Hall effect sensor so as to be capable of determining rotation of the position indicator core without any physical connection being present between the driveshaft position indicator 2 and the position indicator core 3. Various examples have been described, each of which comprise one or more combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. A drive control mechanism comprising:a stator assembly, the stator assembly comprising a plurality of stator windings;a rotor, the rotor comprising:a friction plate; andferromagnetic material;the rotor being rotatably secured to a drive shaft such that the friction plate is located in a plane perpendicular to the rotational axis of the drive shaft so as to form part of an electromagnetic clutch system;the electromagnetic clutch system further comprising a clutch plate connected to the drive shaft, and an armature, the armature comprising ferromagnetic material and being connected to the clutch plate and located opposite to, and in a plane parallel to, the friction plate of the rotor, the armature being biased away from the friction plate so as to leave a gap between the armature and friction plate;wherein the stator windings are located proximal to the armature and the rotor such that passing an electric current through the stator windings creates an electromagnetic field that:activates the electromagnetic clutch by pulling the armature of the electromagnetic clutch into contact with the friction plate of the rotor so as to create a friction lock between the armature and the friction plate; andcontrols the rotational position of the drive shaft;such that the stator windings can only control rotation the drive shaft when the electromagnetic clutch is activated.

2. The drive control mechanism of claim 1, wherein the rotor comprises a plurality of poles oriented parallel to the rotational axis of the drive shaft, the poles comprising ferromagnetic material, and;the stator windings are oriented such that, when a current is passed through the stator windings, the stator assembly creates radial magnetic fields, having first magnetic poles facing away from the drive shaft, and second magnetic poles facing towards the drive shaft, such that the magnetic fields created by the stator windings can act upon the plurality of poles of the rotor so as to control rotation of the rotor.

3. The drive control mechanism of claim 1, wherein the friction plate comprises a plurality of magnetic poles, and the stator windings are oriented such that, when a current is passed through the stator windings, the stator assembly creates axial magnetic fields, having first magnetic poles facing towards the friction plate, and second magnetic poles facing away from the friction plate, and the stator windings control rotation of the rotor via rotation of the friction plate.

4. The drive control mechanism of claim 1, wherein the armature comprises a plurality of magnetic poles, and the stator windings are oriented such that, when a current is passed through the stator windings, the stator assembly creates an axial magnetic field, having first magnetic poles facing towards the armature, and second magnetic poles facing away from the armature, and the stator windings control rotation of the rotor via rotation of the armature.

5. The drive control mechanism of any preceding claim, further comprising a drive shaft position indicator system comprising an indicator sensor and a shaft indicator, the shaft indicator being connected to the drive shaft, and the indicator sensor being positioned proximal the shaft indicator, such that the indicator sensor can detect the rotation of the drive shaft.

6. The drive control mechanism of claim 5, wherein the position indicator system comprises a Hall effect sensor.

7. The drive control mechanism of any preceding claim, wherein the stator assembly further comprises a cooling jacket, the cooling jacket being located proximal to the stator windings and capable of conveying a fluid medium so as to be capable of absorbing, and transferring heat energy away from, the stator windings.A

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