BRIEF DESCRIPTION OF THE DRAWINGS
An example of a preferred embodiment of the dual coil motor system in accordance with the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 is an isometric view of a gantry system that is operable to position an object along an X-Y plane;
FIG. 2 is an isometric view of a linear motor that may be comprised in the gantry system of FIG. 1;
FIG. 3 is an isometric view of a coil bracket of the linear motor comprising multi-phase coils arranged according to the first preferred embodiment of the invention; and
FIG. 4 is an isometric view of a coil bracket of the linear motor comprising multi-phase coils arranged according to the second preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 2 is an isometric view of a linear motor 24 that may be incorporated in at least one of the linear motors 24, 24′ of the gantry system 10 of FIG. 1. The linear motor 24 comprises a magnetic assembly 30 that is preferably stationary, and a movable element, which may be in the form of a coil bracket assembly 32, in which current-carrying coils are mounted onto the movable element. The coils are operative to interact with the magnetic assembly 30 to drive the coil bracket assembly 32 in a direction Y.
In the preferred embodiment, the linear motor is a multi-phase linear motor in which its current-carrying coils are selectively switched over in accordance with the position of the movable coil bracket assembly 32 of the linear motor. This type of linear motor 24 is typically used when long displacement is required, a gantry application being one such example. The magnetic assembly 30 is comprised of portions of high permeability soft iron 34a, 34b and a series of high strength permanent magnets 36a, 36b. The portions of high permeability soft iron 34a, 34b and permanent magnets 36a, 36b are separated by a spacer 38. The spacer 38 can be either a non-magnetic material, such as Aluminum or Stainless steel, or a high permeability soft iron. The spacer 38 is designed such that the coil bracket 32 can be positioned to move freely within the space created between the rows of permanent magnets 36a and 36b.
FIG. 3 is an isometric view of a coil bracket 32 of the linear motor 24 comprising multi-phase coils 40, 42 arranged according to the first preferred embodiment of the invention. It comprises a non-magnetic carrier 44, which is usually made of a low electrical conductivity material such as a fiber reinforced plastic. However, it can also be made from a conductive material such as stainless steel or Aluminum, although this may cause reactionary forces to motion created by eddy currents. The coil bracket assembly 32 further comprises a first coil section 40 and a second coil section 42 wherein the respective coils of the different sections are juxtaposed alongside one another along the same plane. The correct interaction of currents passing through the coil sections 40, 42 with the stationary field assembly 30 will generate a force that is exerted on the coil bracket assembly 32 in the Y direction. The number of coils in the first coil section 40 is a product of the number of electrical phases incorporated in the design and the number of coils per phase required to provide the necessary force. For example, if five coils are required per phase to provide the necessary force and the linear motor 24 has a three-phase topology, then fifteen coils would be used in the first coil section 40.
The first coil section 40 and the magnetic assembly 30 are sufficient for the production of a driving force in the linear motor 24. However, in an application such as the gantry system 10 illustrated in FIG. 1, there exists more than one degree of freedom of motion for the mechanical system. As described above, the gantry system 10 is capable of both linear translation and rotational motion (both produced by the linear motors 24). For optimal control, it would be preferable if the ratio of a moving mass/motor force constant in the linear axis is the same as the moving inertia/torque constant in the rotational axis.
Nevertheless, it is often not possible to obtain such similar moving mass/motor force constant and moving inertia/torque constant ratios mechanically. Hence, the second coil section 42, which has a different motor force constant (or torque constant, when utilized in the rotational axis) as compared to that of the first coil section 40, is mounted next to the first coil section 40 in the same coil bracket assembly 32. Preferably, the second coil section 42 has a lower motor force constant than the first coil section 40. Both coil sections 40, 42 are mounted onto the same coil bracket assembly 32. Thus, the first coil section 40 is operative to substantially drive linear motion of the gantry beam 16 and the second coil section 42 is operative to substantially drive rotary motion of the gantry beam 16.
In the first preferred embodiment shown in FIG. 3, the second coil section 42 has one coil per phase and a total of three phases in the linear motor 24. Hence, there are a total of three coils A2, B2, C2 in the second coil section 42 for driving rotational motion of the gantry beam 16. However, it should be appreciated that it would be feasible to employ any other multi-phase arrangement and any plurality of coils per phase, such that the number of phases in the first coil section is different from the number of phases in the second coil section.
The numbers of individual coil turns in each coil winding of the first and second coil sections 40, 42 are preferably calculated to achieve a similar ratio of moving mass/ force constant and moving inertia/torque constant. The designs of the separate coil sections 40, 42 are also configured to optimize their performance for the same magnetic assembly 30. The coil sections 40, 42 are each energized by a separate power amplifier and are thus independent. During operation of the gantry system driven by the dual coil motors for the application represented in FIG. 1, both coil sections 40, 42 should be operated simultaneously but from two power amplifiers.
FIG. 4 is an isometric view of a coil bracket 32′ of the linear motor 24 comprising multi-phase coils arranged according to the second preferred embodiment of the invention. In this preferred embodiment, the coils of the second coil section 42 are positioned consecutively next to each other, in between the coils of the first coil section 40.
The preferred embodiments of the invention therefore disclose a moving coil arrangement in a linear motor that comprises two groups of coils arranged in one coil bracket, such that when connected to two separate power amplifiers, there are in effect two motors with different force constants. It would be appreciated that, in this way, the described linear motor systems allow for improved motion performance, particularly in the reduction of noise and vibration for systems where it is proposed to use the same motors to control two degrees of freedom in a positioning system.
The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.
Patent Application
20080093936
