Patent Application
20250015654
Aspects of this document relate generally to motors and related methods of manufacture and use. Specific aspects of this document relate to brushless direct current (BLDC) motors using Halbach arrays.
Brushless direct current (BLDC) electric motors are traditionally manufactured primarily from various metals such as steel, copper, and aluminum. While plastic may be used in small quantities for motor components such as insulating barriers, fan blades, and electrical connector housings, they are generally not used for the rotor because a magnetic path is needed for greater efficiency in the magnet circuit. This is generally supplied by what is known in the art as a back-iron. A back-iron is a ferromagnetic ring onto which the magnet structure is attached, typically using industrial adhesives, or a cylinder around the magnets, that forms the return path of flux between adjacent magnets within the rotor. However, back-irons tend to be heavy, increasing the inertial moment of the rotor, and the adhesive process is messy, complex, and prone to misalignment.
BLDC motors generally require external commutation. In particular, a micro-controller is typically used to determine the location of the rotor, and an appropriate magnetic field is generated in the stator to motivate the rotor to spin at the desired speed and direction. Sensored commutation is often accomplished with Hall effect sensors (hereinafter Hall sensors). Typically, three sensors are used, spaced 60 or 120 electrical degrees apart, as is known to one skilled in the art. The sensors measure the magnetic field and digitally trigger when the field passes a threshold. This allows the rotor location to be known to the micro-controller, and thus the stator can be appropriately energized. Sensor-less commutation is done by measuring the counter-electromotive force (counter EMF or back EMF) to determine the location of the rotor magnets relative to the stator. In both cases, slow speed operation of the motor is difficult and imperfect. Sensor-less commutation requires sufficient motor speed to produce measurable back EMF, and thus slow speed operation is difficult to accurately control. Digital Hall sensors only trigger at particular points in the motor's rotation, and so intermediate positions must be interpolated, which limits the accuracy of this control technique at slow speeds, particularly when the force applied by the load changes. In both cases, slow speed control of motors is generally accomplished using external encoders that can more accurately measure the position of the motor, but with added complexity and cost.
Typically, a BLDC motor is controlled using external commutation which requires a separate controller. These controllers must be configured to match the parameters of the motor being controlled, said parameters including motor pole count, motor winding resistance, motor winding inductance, motor rotor inertia, and motor rotational friction. Thus, configuring a BLDC motor for use with a BLDC motor controller is a non-trivial endeavor.
Disclosed herein are motors and related methods for manufacture and use thereof utilizing a polymer rotor (which may by non-limiting example be formed of plastic) to contain the magnet structure without the use of adhesives. A magnetic arrangement known as a Halbach array is used to eliminate the need for a back-iron, and a method for manufacture is introduced that reduces the difficulty in manufacturing a Halbach array.
Further described herein is a means of using two analog Hall sensors to accurately determine the position of the motor. While there exist latching (or digital) Hall sensors, which only have two states, in implementations the motors and related systems and methods herein use analog Hall sensors to accurately track position.
Further described herein is a means of integrating a motor controller and motor driver into the motor itself, allowing a simplified, preconfigured and integrated design to be offered to end users. Additionally, this design reduces the cost of manufacture by eliminating the need for an additional enclosure, connectors, and wires.
Through the use of analog Hall sensors rather than the traditional digital latching Hall sensors typically used in the art, accurate rotation at low speeds becomes possible.
The analog Hall sensors are also used as the basis of an anti-cogging algorithm that feeds forward motor currents based on a knowledge of the rotor position, and with a magnitude such that cogging torque is canceled. The relationship between rotor position and cogging torque is established during motor production, such that the end user is not required to calibrate the motor to enable the anti-cogging capability. This ensures smooth low speed motion.
An integrated fan is utilized to cool both the printed circuit board (PCB) and the motor windings, allowing the motor to operate at higher currents than would ordinarily be possible, even at low speeds.
A through hole is included for simplified wiring and other uses such as routing air for vacuum or cooling and as a means to provide various inserts such as axles and lead screw nuts.
General details of the above-described implementations, and other implementations, are given below in the DESCRIPTION, the DRAWINGS, the CLAIMS and the ABSTRACT.
Implementations will be discussed hereafter using reference to the included drawings, briefly described below, wherein like designations refer to like elements. The drawings are not necessarily drawn to scale.
Implementations/embodiments disclosed herein (including those not expressly discussed in detail) are not limited to the particular components or procedures described herein. Additional or alternative components, assembly procedures, and/or methods of use consistent with the intended motors and related methods of manufacture and use may be utilized in any implementation. This may include any materials, components, sub-components, methods, sub-methods, steps, and so forth.
Referring now to
The stator housing 106 retains a printed circuit board (PCB) assembly 107 and a stator 108 with windings 109 (which are shown in
Referring now to
Referring now to
Referring now to
Referring now to
The rotor may include an alignment mark 306, to provide for manual alignment of the rotor during calibration or for other uses. Cooling fins 307 (which may be hollow) may be utilized to provide airflow to the stator winding while the motor is in motion.
Referring now to
The servos may be programmed to insert an arbitrary number of magnets, in sets of four. Each set of four represents one pole pair. For a rotor with thirteen pole pairs, the following exemplary control sequence could be used: thirteen magnets are inserted into every fourth slot by first inserting the plunger into the slot, removing the plunger, and then rotating the rotor one-thirteenth of a full rotation. This process is repeated thirteen times for each of the thirteen first magnets. The rotor alignment axis is then rotated ninety degrees such that the magnet slots on the rotor are also rotated ninety degrees with respect to the magnets inside the magnet cartridge. The rotor is then advanced one slot, or 1/52th of a full rotation, such that the next thirteen magnets may be inserted, each adjacent to the first thirteen magnets. This process continues until all fifty-two magnets (or thirteen pole pairs) are inserted into the rotor.
An alternative embodiment of the magnet insertion machine is shown in
The rotor inserts into a rotor holder 512 which includes an integrated pulley 513 and is driven by a servo 514 using a toothed pulley 515 and a belt. In this manner, the rotor is made to rotate such that the plunger can insert a magnet into any of the rotor's magnet slots.
The magnets may be inserted in any of four orientations, each ninety degrees apart. Altering the orientation of the magnets by ninety degrees within each adjacent slot is done to construct a Halbach array. These differing orientations are providing using magnet rotation platform 516. The magnet rotation platform is centered about a magnet slot of the rotor. In this way, the magnet rotation slot may be rotated in place while always maintaining linear alignment between the plunger and a magnet slot. Naturally, this works partly because the magnets and the magnet slots each have a square cross-section such that the magnets can be inserted into the slots regardless of the specific rotation. The magnet rotation platform is made to rotate using a stationary toothed belt pulley that is driven by a servo 517 with a toothed drive pulley 518 using a belt.
The magnet cartridge is tall enough to store at least enough magnets to insert all the magnets required to build a complete circular Halbach array. The magnet cartridge can be removed from a cartridge holder 519 to allow easy refilling. Additionally, this allows visual alignment of the plunger with the rotor's magnet slots by sliding the magnet cartridge up and then extending the plunger such that the cartridge then rests upon the upper surface of the plunger. The plunger can then be carefully visually aligned with a particular magnet slot in the rotor, and when the plunger's motion sequence begins, and it initially moves away from the rotor's magnet slot, the cartridge will drop into place, allowing subsequent plunger motion towards the magnet slots to insert magnets. This is due in part to the fact that the cartridge includes a stop that rests atop a cartridge holder, such that when the plunger's motion sequence begins and the plunger retracts, the cartridge (which had been resting atop the plunger) falls by gravity and stops at the appropriate position due to the stop, and the forward plunger motion then inserts a magnet. Note that this alignment may not be needed, in some instances, and in some cases it may be done only for the first magnet (to ensure alignment between the plunger and the first slot), with all remaining magnets being inserted without needing any further alignment—or in some implementations multiple alignment steps may be done. In other implementations the system may be configured for automatic alignment such as using visual or other sensors and alignment motors or the like.
The fan may be always on, or the fan may be activated when more cooling is needed. In the ideal embodiment, a temperature sensor is integrated onto the PCB, and a thermal conductor is placed between the temperature sensor and the stator windings. The temperature sensor communicates with the micro-controller on the PCB to allow the motor controller to determine the temperature of the windings. The temperature sensor may be integrated into the micro-controller itself. The thermal conductor may be an adhesive thermal pad placed on the underside of the PCB (i.e., the side opposite most or all of the PCB's electronic components), such that heat from the windings is substantially routed from the windings, through the thermal pad, through the PCB, and into the micro-controller on the top surface of the PCB (i.e., the surface of the PCB with most or all of the electric components).
The temperature sensor data may be used to control the fan activation or fan speed. The temperature sensor data may also be used to prevent the stator windings from overheating, such as by limiting current flow to the stator windings. Current flow to the windings may also be limited in conjunction with (or after) modeling heat generated by the windings due to instantaneous current flow through the windings (without real-time temperature sensor data) and limiting the current flow based on that model.
This angle is used both to compute the motor's position, and also for the field oriented control (FOC) algorithm that is used to control the voltages that are applied to the motor's three phases.
While the field lines generated by the rotor assembly are roughly sinusoidal, they are not precisely sinusoidal, owing to difference between the strengths of adjacent magnets, spacing between the magnets, and other construction artifacts. In implementations these non-linearities are corrected for programmatically via a calibration step during the manufacturing process. By rotating the motor through a full three-hundred sixty degrees, and comparing the values registered on the Hall sensors to a highly accurate external encoder, deviations from the true linear positions can be determined and compensated for. A mapping from actual 2-argument arctangent (atan 2) output values to corrected (linearized) values can be built by relating the atan 2 output values to the values registered by the accurate external encoder. This information can be used to build a linearization data structure. Specifically, the atan 2 transition from high to low (or low to high) allows the software to determine when the rotor has moved from one pole to the next. An initial alignment step may be used to allow the motor to determine which pole is currently generating the atan 2 output value. For each pole, linearization may be accomplished by means known in the art, or by the method described herein. The method includes fitting a series of linear segments to each atan 2 pole segment. For example, sixty-four linear segments may be fit to the linear segment output for a particular atan 2 pole output. By using a number of linear segments that is a power of 2 (2{circumflex over ( )}n), the first few bits of the atan 2 output value can be used to quickly determine the correct line segment to use to linearize the value returned by the atan 2 result. By storing a slope and offset for each line segment, a mapping can be made from atan 2 values to corrected (linearized) values. In an alternative embodiment, a spline or other non-linear polynomial or other function may be used to map the atan 2 output to a linearized result. In addition to the per-pole linearization data, an overall average of motor poles may be used to linearize the atan 2 output in the event that the current motor pole is not known.
Once a trajectory has been generated, it can be executed (trajectory execution) 902. The trajectory may be broken into a series of target positions, such that each of the series of target positions is sent to the position control loop 903 as a new target position in an evenly time-spaced sequence. For example, a new position from the generated trajectory may be loaded into the position control loop every millisecond. In this way the position control smoothly iterates through all the generated positions, resulting in a smooth and continuous motion profile.
The position control loop 903 may include a proportional-integral-derivative (PID) control loop that attempts to minimize the error between the current target position and the actual position of the motor as measured by the analog Hall sensors. In an alternative embodiment, an external position sensor may be used. This external position sensor may be mounted on the output shaft of a gear reducer as one example, to minimize the error between the measured position and the load being used. The external position sensor may be a dual quadrature encoder, an inductive encoder, or another position sensor type known in the art. The error term calculated by the position control PID loop may be fed to the current control loop 904 as the target torque. In an alternative embodiment, a velocity control loop may be placed between the position control loop and the current control loop, as is known in the art.
The current control loop 904 is a component of the field oriented control algorithm that is used to control the phase winding currents. As is known in the art, the field oriented control method breaks the winding current into two components: the flux current and the torque current. The flux current represents the flux that is perpendicular to the magnets and the phase windings (in other words, the current that does not generate torque). The goal is to minimize the flux current (in other words, keep it at or near zero) and force the torque current towards the target torque. In this way, motor performance can be maximized. This goal is accomplished using two independent proportional-integral (PI) control loops, one for the flux current and the other for the torque current. The inputs to the two control loops are the target torque current, the target flux current (i.e., zero), the actual torque current, and the actual flux current. The actual torque current and the actual flux current may be calculated at a current-sensing step 910 using a process that will be discussed below. The output of the two control loops are the desired flux and torque voltages, which are used as the input to the reverse Park transformation step 905.
The reverse Park transformation 905 takes a desired flux and torque voltage and converts from a rotating reference frame to a stationary reference frame, as is known in the art. These values are then forwarded to the reverse Clarke transformation step 906.
The reverse Clarke transformation step 906 takes the stationary frame flux voltage and stationary frame torque voltage and converts them into the three phase winding voltages, as is known in the art. These three values are then forwarded to the power supply pulse-width modulation (PWM) step 907.
The power supply PWM step 907 takes the rail voltage supplied by the power supply and switches it on-and-off at high speed using the pulse-width modulated technique that is known in the art. Each of the three motor phases is pulse-width modulated to the desired voltage. For example, if the rail voltage is twenty-four volts, and the voltage to the U phase is rapidly switched on and off such that it is on half of the time (50% duty cycle) then the voltage seen by the U phase would be twelve volts. In the preferred embodiment, the PWM step is executed with new target voltages thirteen-thousand times per second. In the preferred embodiment, the PWM “chopping” is at the same frequency, although that is not required. The three chopped phase voltages cause current to flow across the current-sensing resistors (current-sensing step 910) and through the motor phase windings of the stator of the brushless DC motor 911.
The current-sensing step 910 in implementations may begin by sampling three sense resistors. The sense resistors may generate a very small voltage, and so an analog amplification network may be used to boost the gain to levels suitable for sampling by the micro-controller's analog-to-digital converter (ADC). The timing of current sense sampling may be selected to obtain proper low noise readings as is known in the art. One current value may be synthesized by knowledge of the other two through the application of Kirchhoff's voltage law. After acquisition by the micro-controller, the three current values may be sent to the Clarke transformation stage 909.
The Clarke transformation stage 909 takes the three phase current values and converts them into two orthogonal currents representing the stationary reference frame flux current and torque current, as is known in the art. These two currents are then forwarded to the Park transformation stage 908.
The Park transformation stage takes a stationary reference frame flux current and torque current and converts them to a rotating reference frame. This requires knowledge of the rotor's offset as measured between a rotor magnetic pole pair relative to a given motor pole, known as the rotor electrical angle, as is known in the art. In implementations the rotor electrical angle is supplied by the analog Hall sensors, although any other sensor capable of measuring an angular position may be used, such as an optical encoder, inductive encoder, and so forth, as is known in the art. The outputs of the Park transformation are the flux current and torque current values relative to the rotating frame of reference. These values are sent to the current control loop 904, where they close the feedback loop described herein. The properly calculated PWM motor phase currents cause the BLDC motor 911 to spin at the desired torque, jerk, acceleration, velocity, and position.
The analog Hall sensors 912 (which may be the same Hall sensors described previously) may be used to measure the rotor electrical angle and actual position of the motor shaft. In implementations there are two Hall sensors separated by ninety electrical degrees. Data from the two sensors is converted to a position within a pole pair using the inverse tangent (arctan 2) operation, as is known in the art. Other means of calculating electrical angle and rotor position may also be used, as is known in the art. For the actual position, transitions between pole pairs are noted, and the position is incremented appropriately to account for them.
Cogging torque can make smooth low speed motion using a PID loop nearly impossible, as the loop cannot react with sufficient speed to overcome the non-linearity inherent in the cogging. Anti-cogging is a software technique to reduce cogging torque by building a model or map 1001 of the cogging torque imposed by the rotor at different angular positions and feeding a current (and therefore a torque) to the motor for each angular position according to a specification or configuration 1002 such that the feed-forward current cancels the cogging torque for each position. It can be seen how applying the current/torque according to the specification or configuration 1002 acts to neutralize the detected cogging torque illustrated by map 1001. Each peak 1005 that is detected (and is, accordingly, included in the model or map) is neutralized with a counter-peak 1006 in the specification or configuration 1002. The detected troughs 1003 are also echoed by counter-troughs 1004 in the specification or configuration.
Digital Hall sensors do not have sufficient resolution to implement a cogging position map, and so generally an external encoder must be used, at added expense. Additionally, a complex (and error-prone) calibration step must generally be initiated by the end user in order to benefit from anti-cogging capabilities.
By leveraging the high positional resolution of the integrated analog Hall sensing method, or through the use of an external encoder, a high quality cogging map may be built and stored in the motor's micro-controller memory at the time of production or manufacture/assembly, and without requiring a user-initiated calibration step. This allows the end user to benefit from smooth low-speed motion without added expense or complex calibration steps.
Virtual gearing may also be implemented, such that a movement ratio (“gear ratio”) between rotary axes, linear axes, or a combination of rotary and linear axes, is maintained. The movement may key off the goal position or the error position of the master axis, such that all axes stay synchronized in a manner that best suits the application.
More complex relationships such as circular motion, cam action, or wire unspooling, which are known in the art, may also be implemented using the motor network. Raw positional data may also be streamed to multiple axes simultaneously, such that the computing device 1102 can control movement at a fine level of detail, and without use of motor-based motion profile generation. This may be useful, for example, to allow the computing device to translate G-code data into movement data at the motors. This streamed data may be queued (stored in order) by the motors, and kept synchronized by maintaining a common clock time across multiple motors. This moves hard real-time requirements for timing from the computing device to the motors.
The central through-hole may also be designed to accept snap-in or threaded, nut-retained toothed pulleys 1202, axles 1203, and lead screw nuts 1204 of varying sizes, allowing a single motor to easily be customized by either the factory, a reseller, or the end user for use with different axle diameters, different lead screw pitches and diameters, and different uses and configurations. Custom inserts 1205 for particular applications (here a gear) may also be snapped in or retained with a nut. For example, adapters for use with servo horns, custom gears, custom pulleys, or custom bolt patterns may be designed and then three-dimensionally (3D) printed. Other methods of attaching a central axle or other adapter to the motor through-hole may also be used, such as bolts or screws, adhesives, or other attachment methods known in the art or hereafter discovered.
In implementations the control electronics (such as the microcontroller and/or other implementing components used to implement the steps and elements of
Implementations of motors disclosed herein are low-cost, fully integrated, FOC BLDC motors that include external communication and control, motion planning, motion control, and motor power stages. In implementations the motors use low cost polymer (such as plastic) in their design, and are fully integrated to minimize difficulty of use. In implementations a through-hole is included for simplified wiring and other uses such as venting air for vacuum or cooling, and support for various snap-in axles and lead-screws.
Any of the PCBs and PCB assemblies disclosed herein may include multiple components thereon, including a motor controller, a microcontroller, a motor driver, a magnetic rotational position sensor comprising Hall sensors, and so forth. Because the PCB is included/integrated within the motor itself, in implementations in which these components are included in/on the PCB they are, correspondingly, integrated within the motor.
In places where the phrase “one of A and B” is used herein, including in the claims, wherein A and B are elements, the phrase shall have the meaning “A and/or B.” This shall be extrapolated to as many elements as are recited in this manner, for example the phrase “one of A, B, and C” shall mean “A, B, and/or C,” and so forth. To further clarify, the phrase “one of A, B, and C” would include implementations having: A only; B only; C only; A and B but not C; A and C but not B; B and C but not A; and A and B and C.
In places where the description above refers to specific implementations of motors and related methods of manufacture and use, one or more or many modifications may be made without departing from the spirit and scope thereof. Details of any specific implementation/embodiment described herein may, wherever possible, be applied to any other specific implementation/embodiment described herein. The appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this disclosure.
Furthermore, in the claims, if a specific number of an element is intended, such will be explicitly recited, and in the absence of such explicit recitation no such limitation exists. For example, the claims may include phrases such as “at least one” and “one or more” to introduce claim elements. The use of such phrases should not be construed to imply that the introduction of any other claim element by the indefinite article “a” or “an” limits that claim to only one such element, and the same holds true for the use in the claims of definite articles.
Additionally, in places where a claim below uses the term “first” as applied to an element, this does not imply that the claim requires a second (or more) of that element-if the claim does not explicitly recite a “second” of that element, the claim does not require a “second” of that element. Furthermore, in some cases a claim may recite a “second” or “third” or “fourth” (or so on) of an element, and this does not necessarily imply that the claim requires a first (or so on) of that element-if the claim does not explicitly recite a “first” (or so on) of that element (or an element with the same name, such as “a widget” and “a second widget”), then the claim does not require a “first” (or so on) of that element.
As used herein, the term “of” may refer to “coupled with.” For example, in some cases displays are referred to as a display “of” a first computer or computing device, a display “of” a second computer or computing device, and so forth. These terms are meant to be interpreted broadly so that a display “of” a computing device may be a separate display that is, either by wired or a wireless connection, communicatively coupled with the computing device.
The phrase “computing device” as used herein is meant to include any type of device having one or more processors and capable of communicating information using one or more integrated or communicatively-coupled displays, such as a personal computer, a laptop, a tablet, a mobile phone, a smart phone, a personal data assistant (PDA), smart glasses, a tablet, a smart watch, a smart speaker, a robot, any other human interaction device, and so forth.
It is pointed out that the provider of a software application, to be installed on end user computing devices (such as, by non-limiting example, mobile devices) at least partially facilitates an at least intermittent communicative coupling between one or more servers (which host or otherwise facilitate features of the software application) and the end user computing devices. This is so even if the one or more servers are owned and/or operated by a party other than the provider of the software application.
Method steps disclosed anywhere herein, including in the claims, may be performed in any feasible/possible order. Recitation of method steps in any given order in the claims or elsewhere does not imply that the steps must be performed in that order-such claims and descriptions are intended to cover the steps performed in any order except any orders which are technically impossible or not feasible. However, in some implementations method steps may be performed in the order(s) in which the steps are presented herein, including any order(s) presented in the claims.
This document is a bypass continuation application of PCT App. No. PCT/US23/16598, entitled “Motors and Related Methods of Manufacture and Use,” naming as first inventor Roy Sandberg, which was filed on Mar. 28, 2023 and which has an international filing date of Mar. 31, 2022, which PCT application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63/362,309, entitled “Plastic Rotor Halbach Array Motor Machine and Method for Manufacture,” naming as first inventor Roy Sandberg, which was filed on Mar. 31, 2022, the disclosures of which are hereby incorporated entirely herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63362309 | Mar 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US23/16598 | Mar 2023 | WO |
| Child | 18896581 | US |
