WO2001052385A1

WO2001052385A1 - Pre-stack mounting ear

Info

Publication number: WO2001052385A1
Application number: PCT/US2001/001069
Authority: WO
Inventors: Bradley A. Trago; Gregory A. Rittmeyer
Original assignee: Pacsci Motion Control, Inc.
Priority date: 2000-01-13
Filing date: 2001-01-12
Publication date: 2001-07-19

Abstract

A lamination stack (52) having mounting bracket integrally formed herewith. The stator lamination stack (52) is formed by compiling an intermediate stack of laminations and then adding to the intermediate stack, a stack of laminations that have mounting ear extension portions. This stacking may be done automatically in the lamination pressing stage by creating interlocking dimples in each lamination to stake the laminations together. The mounting ear extension portions form a mounting ear (82) when stacked together.

Description

PRE-STACK MOUNTING EAR

BACKGROUND ART Machine designers have long known of the necessity of maximizing their designs both in terms of specific output parameters as well as total overall efficiencies. This driving force is especially important in today's competitive environment where excess design cost, weight, and complexity are no longer acceptable. No place has this driving force been more universally accepted than in the design and manufacture of electric motors.

To reduce cost and weight in the design and manufacture of these motors it is important that no unneeded material be included in the motor design to keep down cost and weight. However, it is also important that enough material be included in the rotor and stator design of these motors to fully utilize the flux available from the expensive permanent magnets which are integral to the design of these machines. The reduction in material in the rotor and stator results in an increased heat dissipation density in the material. This increased density requires a good thermal conductivity path between the machine and the mounting surface in order to dissipate the heat and allow the minimum amount of material to be used.

The standard method that is used is to use a metal end-cap on the mounting end of the machine. The metal-end cap, usually aluminum, acts as a mounting flange and provides good thermal transfer between the motor and the mounting surface. However, the metal-end cap increases the length of the machine assembly which results in increased cost and weight of the machine. DISCLOSURE OF THE INVENTION In view of the foregoing, it is a primary aim of the present invention to provide a mounting bracket for a motor that provides a good thermal conductivity path between the motor and the mounting surface while allowing the minimum amount of material to be used.

It is a further object of the present invention to eliminate the need for an aluminum end-cap to thereby reduce motor cost and weight.

To achieve the foregoing and other objects, one aspect of the present invention is to form mounting ears integral with the stator lamination stack. The stator lamination stack is formed by compiling an intermediate stack of laminations and then adding to the intermediate stack a stack of laminations that have mounting ear extension portions. This stacking may be done automatically in the lamination pressing stage by creating interlocking dimples in each lamination to stake the laminations together. The mounting ear extension portions form a mounting ear when stacked together.

Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:

Figure 1 is a perspective view illustrating a completely assembled motor constructed in accordance with one embodiment of the present invention;

Figure 2 is a partially exploded view showing a motor according to the invention with the rotor assembly removed from the stator assembly; Figure 3 is a cross-sectional view showing a motor assembly constructed in accordance with one embodiment of the present invention;

Figure 4a is a view of an individual stator lamination having a mounting ear integral therewith; Figure 4b is a view of an individual stator lamination;

Figure 5 is a perspective view of the front end of a stator lamination stack made up with the laminations of figure 3;

Figure 6 is a side view of the stator lamination stack of figure 5; and Figure 7 is a perspective view of a motor constructed with an end-cap.

BEST MODE OF CARRYING OUT THE INVENTION

Turning now to the drawings, figure 1 shows a perspective view of a brushless permanent magnet servo motor and figure 3 shows a cross-sectional view of the motor. It should be noted, however, that while the invention is described in connection with a brushless servo motor, it is also applicable to other motor types.

Referring to FIGS. 1-3, there is shown a brushless servo motor generally illustrated by reference numeral 20 comprised of a stator assembly 22 and a rotor assembly 24. The rotor assembly 24 is fitted with bearings 26, 28 and are supported by injection molded end caps 30, 32. The method of forming the injection molded end caps 30, 32 is described in U.S. Patent No. 5,806,169, hereby incorporated in its entirety by reference. It should be noted that conventional metal end caps may also be used.

The rotor assembly 24 is secured into the stator assembly by a retaining ring 34 and a wave preload spring washer 36 pressing against the bearing assembly 28 and the end cap 32. An 0-ring 38 may be used to prevent the bearing assembly 28 from rotating. The rotor assembly 24 includes a rotor shaft 40 which supports a rotor section having permanent magnets 42 attached to rotor lamination section 44 (see Fig 3). After the rotor assembly is installed, a position sensing element 46 is installed on the rotor shaft 40 and a control circuit board 48 is connected to the stator assembly 22. Further details on the position sensing element 46 and its associated control can be found in U.S. Patent Application No. 09/223,943, filed December 31, 1998, hereby incorporated in its entirety by reference.

The end cap 30 has a mounting boss 50. In one embodiment, the mounting boss 50 has a precision machined outer diameter (od) and is used to act as a mounting pilot to locate the motor in a mounting bracket (not shown). The end caps 30, 32 sandwich a stator lamination stack 52 that forms stator poles which carry stator windings (not shown in FIGS. 1 and 2).

Turning now to figures 4-6, the stator lamination stack 52 is formed with laminations 60, 62. Each lamination, which can be formed by stamping, has a series of poles 64. A plurality of teeth 66 may be formed on each pole 64. The poles 64 are separated by gaps 68 which provide an area for receiving the stator windings. Lamination 60 has mounting ear extension portions 70. The mounting ear extension portions 70 have mounting holes 72. In one embodiment, the mounting ear extension portions 70 has a ground hole 74.

A plurality of laminations 62 are stacked together to form a lamination stack 80 of a desired length. The laminations are joined by one or more stamped dimples 76 formed on each pole 64 during the stamping process. It should be noted that in other embodiments, a dimple 76 may not be on every pole 64. Alternatively, a stack can be formed by stacking laminations to a desired height and affixed together by means of welds. Laminations 60 are then stacked onto the lamination stack 80 to form the stator lamination stack 52. The mounting ear extensions 70 form a mounting bracket 82 integral with the stator lamination stack 52. A plurality of stacked laminations 60 is chosen to ensure that the width w of the mounting bracket is of sufficient thickness to adequately support the motor 20 in the application conditions of the motor 20.

Once the stator lamination stack 52 is compiled, an intermediate or unfinished stator assembly is formed. A front insulator 84 and a rear insulator 86 are installed and joined together to provide dielectric isolation between the stator (or coil) windings 88 and the stator lamination stack 52. The coil is wound over the insulators and the coil winding connections are brought out and secured in the rear insulator 86 in predetermined locations for mounting a printed circuit board 48 thereto.

The intermediate stator assembly is then placed into a mold, and molten plastic is injected under pressure into the mold to form the finished stator assembly 22 as described in U.S. Patent No. 6,020,661, hereby incorporated in its entirety by reference. The molten plastic is forced into and fills interior voids in the intermediate stator assembly. Next, a bore is machined through the center of the molded stator assembly to produce a concentric bore for housing the rotor assembly 24; the concentric bore includes mounting surfaces for the rotor assembly bearings 26, 28.

After the molding step is completed, the rotor assembly 24 is installed. This step includes inserting a wave washer 36 to load the bearings in one direction prior to inserting the rotor assembly 24. An 0-ring may be inserted over the bearing 28 to ensure that the bearing 28 does not move. The retaining clip

34 is put into place, completing the installation of the rotor assembly 24. The position sensing element 46 and control circuit board 48 are then installed. The finished servo motor 22 then appears as suggested in figure 1.

It should be noted that the molded plastic material completely covers all of the pole teeth and forms the end caps 30, 32. The molded plastic material also fills all of the voids around the windings. The molded plastic material is selected to have a thermal heat conductivity which is substantially better than that of air, and the motor is thus able to more efficiently conduct heat generated in the stator to ambient.

A motor having a stator lamination stack 52 with integral mounting ear 82 provides a number of advantages over a motor 100 (See Fig. 7) having an end cap 102 with mounting holes 104. One advantage is that the thermal impedance between the stator lamination stack 52 and a mounting surface (not shown) is lower than the thermal impedance of a stator lamination stack 106 mounted to a surface with a metal-end cap 102. The reduction in resistance is due to the mounting ear 82 being integral with the stator lamination stack 52. This eliminates one junction between materials. It also reduces the total sum of junction impedances, which reduces the thermal impedance. This allows the motor to run cooler at a given power output. Alternatively, the power density of the motor can be increased if the motor is operated with the same temperature rise as a motor having a metal end cap.

Another advantage is reduced structural stress of the motor when it is mounted. A metal end-cap 102 is generally made from aluminum in order to reduce weight. The laminations 60, 62 are typically made from M-19 electrical steel that has a hardness of 73 Rockwell B. This hardness is approximately an order of magnitude stronger that that of aluminum. The steel laminations can therefore be exposed to much higher stress levels than an aluminum end-cap can be exposed to before failure occurs. Additionally, the mounting ear is formed from a plurality of laminations, which further increases the structural strength.

Reduced cost is another advantage of the instant invention. With a metal end cap 102, an additional piece must be manufactured and stocked. It also requires the step of attaching the end cap 102 to the motor 100 during final assembly. Attaching the end cap 102 involves either welding, press-fitting, or bonding the end cap 102 to the stator lamination stack 106, or using mounting screws to bolt the end cap 102 to the stator lamination stack 106. A motor having a stator lamination stack 52 with the mounting ear 82 is manufactured and stocked as a single piece and is already assembled prior to final assembly. This eliminates the step of attaching an end cap 102 to the motor during final assembly. The costs saved include the cost of stocking end caps and the final assembly end cap attachment cost. A motor 20 having a stator lamination stack 52 with an integral mounting ear 82 is smaller and lighter than a motor 100 having an end cap 102. This results in a higher power density motor in terms of power output per motor volume. In a motor 100 having an end cap 102 , the stator lamination stack, 106 slides into the end cap 102. This results in the axial length of the motor 100 being longer than the axial length of the motor 20 with integral mounting ears 82.

Additionally, the mounting holes 104 of the end cap 102 are located at a location radially longer than the mounting holes 72 of the instant invention.

All of the references cited herein are hereby incorporated in their entireties by reference. The foregoing description of various preferred 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 forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated.

Claims

CLAIMS:

1. A lamination stack for a stator assembly of a motor, the lamination stack comprising: a first stack portion comprising a plurality of first laminations stacked together in series; and a second stack portion connected to the first stack portion, the second stack portion comprising a plurality of second laminations stacked together in series, the second laminations each having at least one mounting ear that when stacked together form at least one mounting bracket.

2. The lamination stack of claim 1, wherein the first and second laminations are substantially identically shaped excepting for the at least one mounting ear of the second laminations.

3. The lamination stack of claim 1 , wherein the first laminations are generally annular in shape, and wherein the second laminations are generally annular in shape, the at least one mounting ear projecting radially outward from the annularly shaped second laminations.

4. The lamination stack of claim 1 , wherein the first laminations include a plurality of poles defining a plurality of gaps therebetween, and wherein the second laminations include substantially identically sized and shaped poles and gaps to correspond with the first laminations.

5. The lamination stack of claim 1, wherein the at least one mounting ears have a mounting hole that align when the second laminations are stacked together to form a mounting hole in the at least one mounting bracket.

6. The lamination stack of claim 5, wherein one of the at least one mounting ear of the second laminations has a ground hole, the ground holes aligning when the second laminations are stacked together to form a ground hole in one of the at least one mounting bracket.

7. The lamination stack of claim 1, wherein each of the first laminations and each of the second laminations include corresponding dimples, the dimple of each lamination receiving the dimple of adjacent laminations to form the lamination stack.

8. The lamination stack of claim 1 , wherein heat generated within the stator assembly of the motor is dissipated through the at least one mounting bracket of the lamination stack.

9. The lamination stack of claim 8, wherein the lamination stack is coated with a molded plastic material having a thermal heat conductivity better than air.

10. The lamination stack of claim 1, wherein the at least one mounting ear comprises two mounting ears that when stacked together form two mounting brackets.

11. A motor comprising; a rotor assembly having a rotor shaft; a stator assembly housing the rotor assembly, the stator assembly including a lamination stack having a mounting bracket integrally provided therein.

12. The motor of claim I 1 , wherein the annular lamination stack houses stator coils, the lamination stack and stator coils separated by an insulator, the lamination stack, stator coils and insulator being injection molded with plastic to fill interior voids and define two endcaps having the lamination stack disposed therebetween.

13. The motor of claim 12, wherein the molded plastic material has a thermal heat conductivity better than air.

14. The motor of claim 11, wherein heat generated within the stator assembly of the motor is dissipated through the mounting bracket of the lamination stack.

15. The motor of claim 11, wherein the rotor shaft includes a position sensing element and the stator assembly includes a control circuit board in communication with the position sensing element.

16. A lamination stack having a mounting bracket integrally formed therewith.

17. The lamination stack of claim 16 further comprising: a first stack portion comprising a plurality of first laminations stacked together in series; and a second stack portion connected to the first stack portion, the second stack portion comprising a plurality of second laminations stacked together in series, the second laminations each having a mounting ear that when stacked together form the mounting bracket.

18. The lamination stack of claim 17, wherein the second laminations further include another mounting ear to form a pair of ears, the second laminations being stacked together to form a pair of mounting brackets.

19. The lamination stack of claim 16, wherein heat generated within the stator assembly of the motor is dissipated through the mounting bracket of the lamination stack.