Browse Prior Art Database

Linear DC Brushless Motor

IP.com Disclosure Number: IPCOM000042618D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 56K

Publishing Venue

IBM

Related People

Schulz, RA: AUTHOR

Abstract

The usual method of driving printer carriages, x-y plotters, and linear robotic members is to couple a rotary motor to the driven member by a lead screw or belt-pully arrangement which transforms the rotary motion into linear motion. These linkages can be avoided if a linear motor replaces the rotary motor, reducing the cost, weight, backlash, and dynamic complexity, such as belt spring. Linear motors have been known for a long time, but the emphasis has been in the transportation field where the linear induction machine appears to be the most practical. For the kind of mechanisms noted above which have relatively short runs, attaching power and control wires to the moving members is quite possible.

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Linear DC Brushless Motor

The usual method of driving printer carriages, x-y plotters, and linear robotic members is to couple a rotary motor to the driven member by a lead screw or belt-pully arrangement which transforms the rotary motion into linear motion. These linkages can be avoided if a linear motor replaces the rotary motor, reducing the cost, weight, backlash, and dynamic complexity, such as belt spring. Linear motors have been known for a long time, but the emphasis has been in the transportation field where the linear induction machine appears to be the most practical. For the kind of mechanisms noted above which have relatively short runs, attaching power and control wires to the moving members is quite possible. Furthermore, these mechanisms usually need precise position or velocity control, which is obtained much more readily with a DC motor. This can be accompanied by a linear DC brushless motor which is applicable to short run situations where precise velocity or position control is required. A method for constructing a linear DC brushless motor is shown in Fig. 1. The motor consists of two parts: the fixed rod 10 and the moving coils 12. The payload 18 (printhead, recorder pen, etc.) is attached to the moving coils 12. The rod 10 consists of alternating sections of equally spaced permanent magnets 14 and non-magnetic fillers 16. The rod 10 may or may not be the support member of the moving coil 12 assembly. Fundamentally, the motor works like a solenoid or, more accurately, a linear array of solenoids. The payload 18 is propelled by the force between one or more energized coils 12 and the permanent magnet 14 plunger. As a way of explaining this motor, consider only one coil 20 and one permanent magnet 22, as shown in Fig. 2. With the current i flowing in the direction shown in Fig. 2, a force exists between coil 20 and magnet 22, as shown in the accompanying graph. This arrangement will always attempt to pull the coil 20 and magnet 22 into a centered alignment. The coil 20 is equivalent to a permanent magnet which has its north pole on the right and south pole on the left. The situation changes when the coil current i is reversed, as shown in Fig.
3. Now, the coil 20 to magnet 22 force always tries to push the two further apart. The motor works by controlling the polarity and the presence or absence of coil currents in such a way as to cause a continuous motion in the desired direction. Fig. 4 is a diagram showing how the motor is propelled from one magnet 14 to the next. Notice that a coil 12 is always turned off when it is centered over a magnet 14. This is done because here the direction of the forces are critically dependent on position, and they are very large. In this situation, the motor is propelled by the other two coils 12 which are in a well-controlled force region, even though the forces are smaller. In step 1, the middle coil is centered over a permanent magnet 14 so the current through it is turned o...