Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to linear motors. In particular, the present disclosure relates to approaches for minimizing hysteresis effect in linear motors.

BACKGROUND
[0002] Generally, in a linear motor, a linear motion may be obtained by virtue of electromagnetic interaction. As would be understood, position control may be a crucial aspect in the operation of linear motors. Various approaches exist in the art to improve the position control in the operation of linear motors. In one example, a LVDT or motion sensor may be used for obtaining position data. In another example, indirect sensing may be used.

SUMMARY
[0003] Embodiments of the present disclosure relate to linear motors. In particular, the present disclosure relates to approaches for minimizing hysteresis effect in linear motors.
[0004] An embodiment of the present disclosure pertains to a system for minimizing hysteresis effect in a linear motor. The system may include a plurality of MOSFETs configured in a H-bridge. A motor driver may be in communication with the plurality of MOSFETs to control the operation of each of the MOSFETs. A controller may be coupled to the motor driver, and the controller may generate a pulse width modulated signal. Based on the generated signal, the controller may cause the motor driver to cause the plurality of MOSFETs to operate in a first combination and alternately in a second combination. The first combination may include powering on the first and fourth MOSFET and powering off the second and the third MOSFET. The second combination may include powering on the second and the third MOSFET and powering off the first and the fourth MOSFET.
[0005] In another aspect, the motor driver may be a H-bridge motor driver IC.
[0006] In yet another aspect, the plurality of MOSFETs is to operate in the second combination for a short duration of time.
[0007] In yet another aspect, the plurality of MOSFETs may be coupled to a linear motor.
[0008] In yet another aspect, the first combination of the plurality of MOSFETs is to cause the linear motor to operate in a forward polarity.
[0009] In yet another aspect, the second combination of the plurality of MOSFETs is to cause the linear motor to operate in a reverse polarity.
[0010] In yet another aspect, the second combination of the plurality of MOSFETs is to cause the linear motor to operate in the reverse polarity for a short duration of time.
[0011] In yet another aspect, the controller is to further cause the motor driver to modify a drive voltage of the linear motor, based on a duty cycle of the generated pulse width modulated signal.
[0012] In yet another aspect, the operation of the linear motor alternately in the forward polarity and the reverse polarity is to remove a residual magnetism induced in a motor winding of the linear motor.
[0013] An embodiment of the present disclosure pertains to a method for minimizing hysteresis effect in a linear motor. The method may include the steps of: causing a plurality of MOSFETs to operate in a first combination, wherein the plurality of MOSFETs includes a first MOSFET, a second MOSFET, a third MOSFET, and a fourth MOSFET configured in a H-bridge, and wherein the first combination includes powering on the first MOSFET and the fourth MOSFET and powering off the second MOSFET and the third MOSFET; and causing the plurality of MOSFETs to operate in a second combination, wherein the second combination includes powering on the second MOSFET and the third MOSFET and powering off the first MOSFET and the fourth MOSFET.
[0014] In another aspect, the plurality of MOSFETs may be in communication with a motor driver. The motor driver, based on a pulse width modulated signal generated from a controller, is to cause the plurality of MOSFETs to operate in the first combination and the second combination.
[0015] In yet another aspect, the plurality of MOSFETs may be coupled to a linear motor. The first combination of the plurality of MOSFETs is to cause the linear motor to operate in a forward polarity, and the second combination of the plurality of MOSFETs is to cause the linear motor to operate in a reverse polarity.
[0016] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0018] FIG. 1 depicts a position vs voltage curve for a linear motor, as per conventional approaches;
[0019] FIG. 2 depicts an operation of a linear motor, as per conventional approaches;
[0020] FIG. 3 illustrates an exemplary environment including a system for minimizing hysteresis effect in a linear motor and a linear motor in communication with the system, as per an implementation of the present subject matter;
[0021] FIGs. 4A-4B depict exemplary illustrations of the operation of linear motor, as per an implementation of the present subject matter;
[0022] FIG. 5 depicts a flowchart of a method for minimizing hysteresis effect in a linear motor, as per an implementation of the present subject matter;
[0023] FIG. 6 depicts an exemplary plotted curve of flow rate vs duty cycle of an exemplary system, as per an implementation of the present subject matter; and
[0024] FIG. 7 depicts a plotted curve of flow rate vs duty cycle of a conventional system.
DETAILED DESCRIPTION
[0025] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosures as defined by the appended claims.
[0026] Embodiments explained herein relate to linear motors. In particular, the present disclosure relates to approaches for minimizing hysteresis effect in linear motors.
[0027] Generally, in a linear motor, a linear motion may be obtained by virtue of electromagnetic interaction. The interaction may happen between a stationary and a rotating magnetic field. Linear motors may have faster response times and may be frequently used in high accuracy areas of application. As would be understood, position control may be a crucial aspect in the operation of linear motors.
[0028] Various approaches exist in the art to improve the position control in the operation of linear motors. In one example, a LVDT or motion sensor may be used for obtaining position data. The position data may then be used in a closed loop control algorithm to determine the exact position of the motor.
[0029] In another example, indirect sensing may be used. In such cases, the effect of linear motion of the motor may be reflected onto some other process which may then be monitored. The changes in such parameters may drive the control loop governing the motion of linear motor. For example, a flow conditioning circuit including a proportional valve may be used. The proportional valve, based on a linear motor, may control the flow in the pneumatic circuit and the flow readings may be used to control the valve. This approach may also be referred to as a closed loop control method.
[0030] However, such conventional and existing approaches for improving the position control in the operation of linear motors may be based on closed loop control approaches. Approaches where open loop control may be used for driving linear motors may not be used, owing to the presence of hysteresis effect. The hysteresis may cause a hindrance in the operation of the linear motor. When the voltage is reduced and the linear motor is caused to switch to reverse polarity from forward polarity, a divergence may appear due to hysteresis. This may result in a position error. This has been depicted in FIGs. 1-2.
[0031] FIG. 1 depicts a position vs voltage curve for a linear motor as per conventional approaches, and FIG. 2 depicts an operational linear motor as per conventional approaches. Both the curves as depicted in FIG. 1 represents the forward polarity region which start from origin i.e. 0 volts to point C i.e. V_c volt. At point C, the voltage is reduced and brought down to 0 volt which follows the red curve. An ideal motor without the effect of hysteresis would follow the white curve in both conditions, however, due to hysteresis effect, the curves diverge. The red curve does not end up at the origin thus there is a position error. If examined at V_a volt, we get 2 points A and B in white and red curves respectively. The corresponding error due to hysteresis at this point is calculated as:
Error in position =
[0032] As a result of this, the open loop of the linear motor may be difficult to implement.
[0033] To this end, approaches for minimizing hysteresis effect in linear motors are described. As would be appreciated, the approaches of the present subject matter may minimize the hysteresis effect in the linear motor, thereby improving the open loop control of the linear motor. The proposed approaches may further reduce the difference in the position in the forward and reverse polarity of the linear motor, thereby further minimizing the error due to hysteresis, and resulting in easier implementation of open loop control of linear motors.
[0034] These and other aspects have been described in further details in conjunction with FIGs. 3-7. It may be noted that these figures are only illustrative, and should not be construed to limit the scope of the subject matter in any manner. It may be further noted that the FIGs. 3-4 have been explained together for describing the proposed approaches for minimizing hysteresis effect in linear motors, and same reference numerals have been used wherever necessary.
[0035] FIG. 3 illustrates an exemplary environment including a system 300, as per an implementation of the present subject matter. The system 300 may be in communication with a linear motor 302, and is to minimize hysteresis effect in the linear motor 302. In one example, as depicted in FIG. 3, the system 300 may be implemented as a circuit. In another example, the system 300 may be implemented as a combination of devices. Any other structural or logical implementation of the system 300 may also be possible, and would be covered within the scope of the present subject matter.
[0036] The system 300, circuit 300 in the present example, may include a plurality of MOSFETs 304-1, 304-2, …., 304-N (collectively and individually referred to as MOSFET 304). In one example, as depicted in FIG. 3, the plurality of MOSFETs 304 may include a first MOSFET 304-1, a second MOSFET 304-2, a third MOSFET 304-3, and a fourth MOSFET 304-4. The four MOSFETs, as depicted in FIG. 3, may be configured in a H-bridge. However, it may be noted that the same is done only for the sake of example and may not be construed to limit the scope of the present subject matter in any manner. Any other combination of MOSFETs may also be possible and would lie within the scope of the present subject matter.
[0037] Continuing further, a motor driver 306 may be in communication with the plurality of MOSFETs 304. In one example, the motor driver 306 may be H-bridge motor driver IC. The motor driver 306 is to control the operation of each of the plurality of MOSFETs 304. In one example, as depicted in FIG. 3, the gate signal of each of the plurality of MOSFETs may be controlled by the motor driver 306. Further, a controller 308 may be coupled to the motor driver. The controller 308 may be understood as any hardware-based or software-based processing device known to a person skilled in the art. In one example, the controller 308 may be a dual way micro-controller. Any other example would also lie within the scope of the present subject matter.
[0038] The controller 308 may generate a pulse width modulated signal 310. Based on the generated signal 310, the controller 308 may cause the motor driver 306 to control the operation of the plurality of MOSFETs 304. The controller 308, through the motor driver 306, may cause the plurality of MOSFETs to operate alternately in forward polarity and reverse polarity.
[0039] In operation, as a first step, the motor driver 306, based on the generated signal 310 from the controller 308, may cause the plurality of MOSFETs to operate in a first combination. The first combination may include powering on the first MOSFET 304-1 and the fourth MOSFET 304-4, while powering off the second MOSFET 304-2 and the third MOSFET 304-3. As described previously, the plurality of MOSFETs may be coupled to the linear motor 302. The first combination of the plurality of MOSFETs is to cause the linear motor 302 to operate in a forward polarity. This has been depicted in FIG. 4A. FIG. 4A depicts exemplary illustration of the operation of linear motor 302 in forward polarity.
[0040] Continuing further, as a second step, the motor driver 306, based on the generated signal 310 from the controller 308, may thereafter cause the plurality of MOSFETs to operate in a second combination. The second combination may include powering on the second MOSFET 304-2 and the third MOSFET 304-3, while powering off the first MOSFET 304-1 and the fourth MOSFET 304-4. The second combination of the plurality of MOSFETs is to cause the linear motor 302 to operate in a reverse polarity. This has been depicted in FIG. 4B. FIG. 4B depicts exemplary illustration of the operation of linear motor 302 in reverse polarity. The plurality of MOSFETs 304 may operate in the second combination for a short duration of time. This may result in the operation of the linear motor 302 to operate in the reverse polarity for a short duration of time.
[0041] As would be further noted, the controller 308, through the motor driver 306, may also be able to modify a drive voltage of the linear motor 302. This may be done based on a duty cycle of the generated pulse width modulated signal 310. For example, the controller 308 may increase the duty cycle of the generated signal 310. This may, in turn, result in increase in the drive voltage of the linear motor 302. Similarly, the controller 308 may also decrease the duty cycle of the generated signal 310. This may, in turn, result in decrease in the drive voltage of the linear motor 302.
[0042] As would be furthermore noted and appreciated, the operation of the linear motor 302 alternately in the forward polarity and the reverse polarity may aid in removing a residual magnetism induced in a motor winding of the linear motor 302. Reversing the polarity of the linear motor 302 may cause the induced magnetic field of the linear motor 302 to polarize in the opposite direction, thereby nullifying the induced residual magnetism. The reverse polarization voltage may depend on the strength of the magnetic field induced and the material of the core.
[0043] FIG. 5 depicts a flowchart of a method 500 for minimizing hysteresis effect in a linear motor, such as linear motor 302, as per an implementation of the present subject matter. The method 500 may be implemented in the system 300 as described in conjunction with FIG. 3.
[0044] At block 502, a plurality of MOSFETs 304 may be caused to operate in a first combination. The plurality of MOSFETs may include a first MOSFET 304-1, a second MOSFET 304-2, a third MOSFET 304-3, and a fourth MOSFET 304-4 configured in a H-bridge. The first combination may include powering on the first MOSFET 304-1 and the fourth MOSFET 304-4, and powering off the second MOSFETE 304-2 and the third MOSFET 304-3.
[0045] At block 504, the plurality of MOSFETs 304 may be caused to operate in a second combination. The second combination may include powering on the second MOSFET 304-2 and the third MOSFET 304-3, and powering off the first MOSFET 304-1 and the fourth MOSFET 304-4.
[0046] The proposed approach for minimizing hysteresis effect in the linear motor 302 was experimentally verified. The proposed approach of control was applied to a linear motor based proportional valve, in a flow conditioning circuit. A flow sensor was used to measure the flow rate of air through the circuit. A control signal was given to the proportional valve in accordance with the proposed approach and the effect was observed by recording the flow rate through the flow sensor. It may be noted that any change in the hysteresis behaviour of the linear motor 302 would then be directly reflected on the flow and then consequently in the flow rate.
[0047] The duty cycle of the pulse width modulated signal 310 was mapped from 0 to 4000, i.e., value 0 is equal to 0% duty cycle and value 4000 is equal to 100% duty cycle. The experiment was conducted by increasing the duty cycle of the signal 310 which drives the proportional valve. This caused the flow to increase. After a certain max duty cycle value, the duty cycle is then reduced gradually, resulting in closing of the valve. The flow rate vs duty cycle relation was plotted. FIG. 6 depicts an exemplary plotted curve of flow rate vs duty cycle of the system 300, as per an implementation of the present subject matter.
[0048] The aforementioned steps were again performed, however, this time, whenever the successive duty cycle is less than the current duty cycle, the direction of drive was reversed, and a duty cycle equal to the current duty was supplied for a duration of 3 milliseconds. After this time interval, the reduced duty was given as required in the original drive direction. The aforementioned performance and the curvature were compared with the conventional flow rate. This has been depicted in FIG. 7. FIG. 7 depicts a plotted curve of flow rate vs duty cycle of a conventional system.
[0049] The difference in the offset values at value 1300 in first scenario was found to be 11.84 lpm, and at the same duty cycle in the second scenario was 6.92 lpm. The improvement in the performance is nearly 41 %.
[0050] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art. , Claims:1. A system to minimize hysteresis effect in a linear motor, the system comprising:
a plurality of MOSFETs, wherein the plurality of MOSFETs comprises a first MOSFET, a second MOSFET, a third MOSFET, and a fourth MOSFET configured in a H-bridge;
a motor driver in communication with the plurality of MOSFETs, wherein the motor driver is to control the operation of each of the plurality MOSFETs; and
a controller coupled to the motor driver, wherein the controller is to generate a pulse width modulated signal, and wherein the controller, based on the generated signal, is to cause the motor driver to:
cause the plurality of MOSFETs to operate in a first combination, wherein the first combination comprises powering on the first MOSFET and the fourth MOSFET and powering off the second MOSFET and the third MOSFET; and
alternately cause the plurality of MOSFETs to operate in a second combination, wherein the second combination comprises powering on the second MOSFET and the third MOSFET and powering off the first MOSFET and the fourth MOSFET.

2. The system as claimed in claim 1, wherein the motor driver is a H-bridge motor driver IC.

3. The system as claimed in claim 1, wherein the plurality of MOSFETs is to operate in the second combination for a short duration of time.

4. The system as claimed in claim 1, wherein the plurality of MOSFETs is coupled to a linear motor.

5. The system as claimed in claim 4, wherein the first combination of the plurality of MOSFETs is to cause the linear motor to operate in a forward polarity.

6. The system as claimed in claim 4, wherein the second combination of the plurality of MOSFETs is to cause the linear motor to operate in a reverse polarity.

7. The system as claimed in claim 6, wherein the second combination of the plurality of MOSFETs is to cause the linear motor to operate in the reverse polarity for a short duration of time.

8. The system as claimed in claim 4, wherein the controller is to further cause the motor driver to modify a drive voltage of the linear motor, based on a duty cycle of the generated pulse width modulated signal.

9. The system as claimed in claim 4, wherein the operation of the linear motor alternately in the forward polarity and the reverse polarity is to remove a residual magnetism induced in a motor winding of the linear motor.

10. A method for minimizing hysteresis effect in a linear motor, the method comprising:
causing a plurality of MOSFETs to operate in a first combination, wherein the plurality of MOSFETs comprises a first MOSFET, a second MOSFET, a third MOSFET, and a fourth MOSFET configured in a H-bridge, and wherein the first combination comprises powering on the first MOSFET and the fourth MOSFET and powering off the second MOSFET and the third MOSFET; and
causing the plurality of MOSFETs to operate in a second combination, wherein the second combination comprises powering on the second MOSFET and the third MOSFET and powering off the first MOSFET and the fourth MOSFET.

11. The method as claimed in claim 10, wherein the plurality of MOSFETs is in communication with a motor driver, and wherein the motor driver, based on a pulse width modulated signal generated from a controller, is to cause the plurality of MOSFETs to operate in the first combination and the second combination.

12. The method as claimed in claim 10, wherein the plurality of MOSFETs is coupled to a linear motor, and wherein:
the first combination of the plurality of MOSFETs is to cause the linear motor to operate in a forward polarity; and
the second combination of the plurality of MOSFETs is to cause the linear motor to operate in a reverse polarity.