Title: Compound Motor

Technical field of the invention

This invention relates to a motor drive suited for high speed precision movement.

Background to the invention

The applicant is aware that driving increasingly heavier loads require larger more powerful motors with increasing inherent rotational inertia of the motor. The inherent rotational inertia of the motor increases the spin-up time for the motor to reach its working speed and the spin-down time needed to come to a stop. Larger motors also have a larger time constant. It is an object of this invention to provide a motor drive wherein the effect of the inherent inertia and time constant is reduced to enable faster positioning of the drive. It is an object of this invention to provide a drive with an improved rotational dynamic response with a short time required to move a load from start to stop for a given angular movement.

General description of the invention

According to a first aspect of the invention there is provided a motor drive, which drive includes: at least two motors which input energies are synchronised; and a mechanical directly proportional link for linking the motors.

Motors of the same specification will not need additional gearing to be directly proportionally linked, and it is preferred to have all the motors of the same relevant specification.

In the case of electrical motors, the stators and rotors are also electrically phase aligned. For applications where the drive needs to be able

to come to a stop in any position, the preferred motor is a brushless servo motor, preferably a 3 phase AC motor. For applications where the drive comes to a stop at predetermined positions, such as in assembly lines, a stepper motor can be used.

One of the motors of the motor drive may include a position sensor, which motor is configured to be the reference motor for controlling all the motors of the drive. The position sensor may preferably be an angular position sensor. The sensor and/ or motor may also be synchronised with an action by a payload moved by the drive, in use, and/ or a braking system for bringing the drive to a stop in a specific position.

The motor with the position sensor may be configured to control a current for synchronised driving of all the other drives.

The position sensor can also be used to provide commutation current between phases to drive the motor to an angular position between phases.

The position sensor can also be configured to provide a signal or feedback signal for actuating a braking system or an action by a payload such as firing a round as a countermeasure against an incoming rocket or missile or the like.

The mechanical directly proportional link may be selected from gears such as spur gears, helical gears, planetary gears, rack and pinion and worm and wheel configurations. The preferred mechanical link is a ring and pinion gear configuration, which provides high stiffness for quick and accurate response times. The pinion gear may be inside or outside the ring gear.

The mechanical directly proportional link may preferably be a single circular gear connected to each of the motors in electrical phase alignment. It will be appreciated that this preferred embodiment provides maximum gear stiffness.

Alternatively, the mechanical directly proportional link may be selected from a chain drive, cable drive, or steel belt drive.

The position sensor my include any one or more of the devices selected from a mechanical encoder, an optical encoder, a magnetic pulse resolver, inductive position sensor, hall effect sensors and the like rotary or linear position sensors. Absolute encoders are preferred where the memory of the position without requiring movement of the motor is needed.

The motor drive may also include a braking system. The braking system may include a disc and a plate configured to engage frictionally. The braking system may include a hydraulic actuator for urging the disc and plate together. The hydraulic actuator may in turn be actuated by an electrical drive. The hydraulic actuator may include a plurality of slave cylinders driven by a master cylinder. The master cylinder may in turn be driven by an electrical linear motor.

The motor drive may include a control system for controlling the drive.

The control system may include a processor which may be configured to provide or withhold energy to the drive in response to a signal from the position sensor. The processor may be configured to provide energy to a braking system of the drive in response to a signal from the position sensor.

The processor may be configured to actuate an action by a load carried by the drive in response to a signal from the position sensor.

Detailed description of the invention

The invention is now described by way of example with reference to the accompanying drawings.

In the drawings:

Figure 1 shows schematically a perspective view of a motor drive, in accordance with the invention; Figure 2 shows schematically a plan view of the motor drive; and

Figure 3 shows schematically a sectional side view of the motor drive.

Referring now to the drawings, the motor drive, in accordance with the invention, is generally indicated by reference numeral 10.

In the embodiment shown, the motor drive 10 includes 8 identical electrical AC servo motors 12 operating from a 565 Volt DC bus. The stators and rotors of each motor are electrically phase aligned. The input energies are synchronised by means of one angular sensor in the form of an encoder 14 fitted to one of the motors 12.1. The motor 21.1 is configured to be the reference motor for controlling all the motors of the drive. The current for the rest of the motors 12 are commutated from the motor 12.1.

The motor drive 10 further includes a mechanical directly proportional link for linking the motors in the form of a circular ring gear 16 which axis defines the axis of the motor drive 10. The circular gear is connected to each motor 12 by means of the pinion drive gears 18 connected to the drive shaft of each motor 12. The motors 12 are fixed in position.

The motor drive includes a braking system 20. The braking system includes a disc 22 and a plate 24 configured to engage frictionally. The braking system includes a hydraulic actuator for urging the disc 22 and plate 24 together. The hydraulic actuator includes a plurality of slave cylinders 26 driven by a master cylinder (not shown). The master cylinder is in turn driven by an ironless linear electrical motor (not shown) with a time constant of less than one millisecond.

The motor drive 10 compared to a single motor, in accordance with the invention, achieves the high dynamic response due to the improved characteristics of a lower effective rotational inertia, lower total motor mass, and shorter electrical time constant. Additionally, the division of the motor drive torque over a number of smaller inputs allows small gears made of a lightweight material such as aluminium compared to a single motor which requires a higher mass and inertial planetary gear drive or similar drive.

Table 1 shows a comparison between a single motor and a motor drive (compound motor) for a similar payload.

Table 1

The motor drive 10 includes a control system (not shown) for controlling the drive. The control system includes a processor which is configured to provide or withhold energy to the drive in response to a signal from the position sensor 14. The processor is configured to provide energy to a braking system 20 of the drive in response to a signal from the position sensor. The processor is configured to actuate a round to be fired by a grenade launcher carried by the drive in response to a signal from the position sensor and other inputs to the processor relating to a countermeasure.

It will be appreciated that the motor drive in accordance with the invention can be used for improved high energy-efficient motors for wheel drives, military applications such as high speed weapon drives, and industrial rotary or linear placement drives.

It shall be understood that the example(s) is/ are provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and are not meant to be construed as unduly limiting the reasonable scope of the invention.