FEEDBACK”

FIELD OF THE INVENTION

The present invention provides an improved stepper motor based linear actuator with position feedback. More particularly, the present invention provides stepper motor based linear actuator with position feedback that enables the linear actuator to reach target position and compensate step loss in stepper motor.

BACKGROUND OF THE INVENTION

A linear actuator is a device that develops a force and a motion through a straight line. A stepper motor based linear actuator uses the stepper motor for rotary power. In the stepper motor, there is a threaded precision nut instead of a shaft and the shaft is replaced with a lead screw. With rotation of rotor, linear motion is achieved directly through the nut and threaded screw. The electric pulses are transformed into angular displacement. When a pulse signal is received, the stepper motor rotates a fixed angle performing rotary action according to the direction set for the stepper motor. The rotational velocity and acceleration of motor can be controlled by the pulse frequency to achieve the purpose of speed control. Also, it is brushless, synchronous electric motor that can device a full rotation into an expansive number of steps.

Stepper motor is used widely due to its precision, high torque at startup and low speed, ruggedness, simplicity of construction, low maintenance, and so on. Some of the applications includes intake valve drive used in idling control of two wheelers specially bikes, intake systems, thermal expansion valves, exhaust systems, suspension control and meter display drive etc. The stepper motor as linear actuator is a form of permanent magnet stepper motor consists of two stators and two coils stacked on the top of each other. The rotor consists of a permanent magnet and it has the same number of pole pairs that each stator has. Unlike other rotary motors, steppers are unique in that they move a given amount of rotary motion for every electrical input pulse. This makes steppers a perfect solution for use in positioning applications. Generally, there is no feedback system provided in stepper motor as linear actuator in state of the art to detect the position of the actuator and to compensate the step loss thereof, due to this step loss in stepper motor as linear actuator may happen and may not be detected which may cause loss in precision control.

Commonly, the stepper motor as linear actuator consists of various components including but not limited to a plurality of wire winding coils, a stator, a rotor, an assembly to provide linear movement of the pintle/actuator, terminals to supply electricity, bearing, stator cup, bobbin etc. Increase in load or friction causes step loss in stepper motor which consequently causes step loss in linear actuator.

Patent document US7589445B2 discloses a linear actuator includes a brushless polyphase synchronous electric motor having a stator and a rotor. The rotor acts on a control element via a driver which can transform the rotation movement thereof into a linear movement over several rotations. Preferably, the inventive actuator comprises elastic and/or magnetic return device which can systematically return the control element to a reference position when the power supply to the motor is cut. The motor has a position detection device which, together with an electronic control unit, is used for the automatic control and regulation of the position of the rotor and, therefore, the control element. In this document gear arrangement is used for linear motion which is less precise than stepper motor based linear actuators.

Therefore, there is a need of a technology to provide the feedback and step loss compensation of the actuator in stepper motor as linear actuator to improve efficiency and long working hours of the said stepper motor based linear actuator.

OBJECT OF THE INVENTION

The main object of the present invention is to provide a stepper motor based linear actuator with position feedback that enables reaching target position without step loss. Another object of the present invention is to provide a stepper motor based linear actuator that is able to compensate step loss in stepper motor.

Yet another object of the present invention is to provide a stepper motor based linear actuator with enhanced actuator efficiency. Still another object of the present invention is to provide stepper motor based linear actuator with hall sensor and linear magnet incorporated to control linear position of stepper motor based linear actuator pintle.

SUMMARY OF THE INVENTION

The present invention relates to a stepper motor based linear actuator with actuator position feedback and provides compensation to step loss. More particularly, the present invention provides stepper motor based linear actuator that incorporates a hall sensor and linear magnet and provides position feedback of pintle along with compensating step loss in stepper motor.

In an embodiment of the present invention, a stepper motor based linear actuator is provided comprising of a housing, a printed circuit board (PCB) assembly, a plurality of motor terminals, a plurality of claw plate and respective claw cup, a plurality of coil, a bobbin assembly, a sealing jacket, a plurality of bearings, a rotor assembly, a spring and an actuator sub-assembly. Wherein, said actuator sub-assembly comprises of a pintle and at least one magnet holder fitted with a linear magnet at the distal end of the said pintle. When stepper motor gets electrically energized, the actuator changes its position linearly, which changes the magnetic flux. Further, the PCB assembly comprises of at least one hall sensor attached on the PCB, a plurality of sensor terminals and a potting at the rear side of PCB. Said hall sensor detects the changes in magnetic flux and provides feedback to the driver i.e. electronic control unit, also said hall sensor enables compensation to the step loss generated in the stepper motor based linear actuator.

Hence, the present invention provides a stepper motor based linear actuator with actuator position feedback and compensation to the step loss in stepper motor with reduced complexity.

BRIEF DESCRIPTION OF THE DRAWING

An understanding of the system and method of the present invention may be obtained by reference to the following drawings:

Fig. 1 illustrates a sectional view of stepper motor based linear actuator in accordance with the present invention. Fig. 2 illustrates an exploded view of the stepper motor based linear actuator in accordance with the present invention.

Fig. 3 illustrates assembling magnet holder in the pintle in accordance with the present invention.

Fig. 4(a) illustrates assembling PCB assembly in the housing of the stepper motor based linear actuator in accordance with the present invention.

Fig. 4(b) illustrates assembling the potting at the rear side of the PCB assembly in the housing of the stepper motor based linear actuator in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Many aspects of the invention can be better understood with references made to the drawings below. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating the components of the present invention. Moreover, like reference numerals designate corresponding parts through the several views in the drawings. Before explaining at least one embodiment of the invention, it is to be understood that the embodiments of the invention are not limited in their application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The embodiments of the invention are capable of being practiced and carried out in various ways. In addition, the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

In a most preferred embodiment, the present invention provides a stepper motor based linear actuator with position feedback that enables compensation of step loss in stepper motor. Said stepper motor based linear actuator comprises of a housing, a stepper motor, a PCB assembly, a plurality of motor terminals, a plurality of claw plate and respective claw cup, a plurality of coil, a bobbin assembly, a sealing jacket, a plurality of bearings, a rotor assembly, a spring and an actuator sub-assembly. Said bobbin assembly comprises a plurality of bobbin stacked one over other. Said actuator sub-assembly comprises of a pintle and at least one magnet holder fitted with a linear magnet at the distal end of the said pintle. When stepper motor gets electrically energized, the actuator changes its position linearly, which changes the magnetic flux. Further, the PCB assembly comprises of at least one hall sensor attached on the PCB, a plurality of sensor terminals and a potting at the rear side of PCB. Said hall sensor detects the changes in magnetic flux by the linear magnet and provides feedback to the driver i.e. electronic control unit. On receiving the position feedback, the driver controls the linear position change in pintle. The position feedback taken helps to compensate the step loss in stepper motor.

Here, the magnet holder is made of a material that does not alter the magnetic flux and includes but is not limited to plastic of uniform thickness. Said sealing jacket is provided to separate stator i.e. bobbin assembly from the rotor assembly. The linear magnet is assembled into the magnet holder by a method including but not limited to snap fitting, interference fitting, press fitting, overmolding etc. Further, the magnet holder is assembled with the pintle by a method including but not limited to snap fitting, interference fitting, press fitting, overmolding, screw joint etc.

Fig. 1 shows a sectional view of the stepper motor based linear actuator (50) as per the present invention. Said stepper motor based linear actuator (50) comprises of a housing (1), a plurality of sensor terminal (14), a bobbin assembly comprising a plurality of bobbins (21), plurality of coils (22), a plurality of bearing (31), a sealing jacket (2), a pintle (41), at least one spring (44), a plurality of motor terminal (25), a rotor assembly (32), a magnet holder (42), at least one linear magnet (43), a PCB assembly. Wherein said magnet holder (42) is made of material including but not limited to plastic, non magnetic material or like and is provided with a hollow area, and said linear magnet (43) is assembled in the said hollow area. Further, said bobbins (21) are stacked. The sealing jacket (2) separates the rotor assembly from the stator i.e. the bobbin assembly and is preferably made of a waterproof material including but not limited to steel or thermoplastic of uniform thickness lying in the range of 0.1mm to 1mm. The pintle (41) has a top end (41a) and a bottom end (41b).

Fig. 2 shows an exploded view of the stepper motor based linear actuator (50) in accordance with the present invention. Said stepper motor based linear actuator (50) comprises of a housing (1) that has a provision to attach a PCB (11) incorporated with a hall sensor (12) and a plurality of sensor terminals (14) preferably three sensor terminals that are attached to said PCB (11). A bobbin assembly is provided comprising of a plurality of bobbins (21) stacked one over other having a plurality of motor terminals and wound with a plurality of coils (22) assembled between a plurality of claw plates (23) and respective claw cups (24). A sealing jacket (2) is assembled such that the rotor assembly (32) with a plurality of bearings (31), and an actuator assembly are inserted inside and are separated from the stator i.e. bobbin assembly, coils etc. Said actuator assembly (50) further comprises of a pintle (41), a magnet holder (42), a permanent linear magnet (43) and a spring (44).

Fig. 3 illustrates assembling magnet holder in the pintle in accordance with the present invention. The magnet holder (42) on top end has snap fitting hooks (42a) and below has a hollow area in which a linear magnet (43) gets fitted by a method including but not limited to snap fit, over-molded, screw joint or like. The pintle (41) has a top end (41a) and a bottom end (41b), wherein the bottom end (41b) is provided with a snap-fit design that attaches to the snap fitting hooks (42a) of the magnet holder (42). The pintle (41) and magnet holder (42) are connected by a method including but not limited to press fit, over-molding, screw joint or like. Said pintle has a screw threads in bottom half portion. The length of linear magnet (43) is based on total travel requirement. Total travel requirement is length which the linear magnet has to travel and is based on specification of linear actuator.

Fig. 4(a) illustrates assembling PCB assembly in the housing of the stepper motor based linear actuator in accordance with the present invention. The PCB assembly (11) having a hall sensor (12) and plurality of terminals (14) fused over PCB is inserted into a provision in the housing (1) having connection pins (16) for the plurality of sensor terminals (14). The hall sensor (12) is placed on the PCB (11), such that it is parallel to linear magnet (43). The PCB (11) is assembled outside and then inserted into provision in the housing (1). The sensor terminals (14) connect with the connection pins (16) through snap fit, soldering or like. In an alternate embodiment, the hall sensor (12) is placed perpendicular to the linear magnet (43).

Fig. 4(b) illustrates assembling the potting at the rear side of the PCB assembly in the housing of the stepper motor based linear actuator in accordance with the present invention. After the PCB assembly is inserted in the housing (1), a potting (13) i.e. a low pressure molding or epoxy is done at the rear of the PCB assembly to close the provision in the housing (1). Therefore, the present invention provides a stepper motor based linear actuator with position feedback which enables the pintle to reach target position without step loss. The stepper motor based linear actuator is useful in applications where precise motion is required with force and position feedback. The foregoing description of embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principals of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.