Patent Publication Number: US-2010117679-A1

Title: Test apparatus, system, and method having a magnetic feature

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This document is a continuation application that is related to, and claims priority from U.S. patent application Ser. No. 11/549,587, entitled “Test Apparatus, System, and Method With a Magnetic Feature,” and filed on Oct. 13, 2006, which is commonly owned, and which is hereby incorporated by this reference in its entirety. 
    
    
     GOVERNMENT RIGHTS 
     The present invention was made with support of the government under Office of Naval Research, Contract No. N00014-04-C-0618. The Government may have certain rights in the present invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a test apparatus for testing a brush and a brush holder. More specifically, the present invention relates to a test apparatus for testing brushes and brush holders in the presence of a magnetic field. 
     2. Discussion of the Related Art 
     Evaluation of multi-conductor metallic brushes for electric propulsion motors and generators is important in assuring reliable operation of the motors, generators, vehicles, or vessels with which they are utilized. The complex operational environment of a large number of brushes can be simulated by a computer program; however, preferable is that the computer results be validated by laboratory testing. Additionally, brushes can be evaluated after being actually used in a motor; however, these brushes are not easily accessible. Furthermore, in many instances, disassembling the motor during use in order to evaluate the brushes is impractical. Previously, brushes have been evaluated using a test apparatus that includes a motor driven rotor. The brushes are held in contact with the rotor; and the wear on the brushes can be evaluated. However, this type of test apparatus lacks many real world applications. 
     Motors and generators can be subjected to high magnetic field strengths and varying environmental conditions while in use. These high varying magnetic fields and varying environmental conditions, possibly present in electric propulsion motors and generators, create a need for an apparatus to simulate the conditions of the motors and generators. Thus, a need exists for a measurement apparatus that can test brushes and brush holders under varying magnetic fields as well as varying environmental conditions. 
     SUMMARY OF THE INVENTION 
     The present embodiments provide a test apparatus, system, and method for testing many brushes and brush holders under a varying magnetic field as well as a plurality of varying environmental conditions. The present test apparatus for testing a plurality of brushes and brush holders under a varying magnetic field can be used with measurement instruments to evaluate the performance of the brushes and brush holders within controlled operating conditions. 
     One embodiment can be characterized as a test apparatus, comprising a rotor coupled to a drive shaft, wherein the drive shaft is mechanically coupled to a drive system. The apparatus comprises a stator coupled to at least one brush holder and at least one brush held by the at least one brush holder, wherein the at least one brush is held in contact with the rotor. The test apparatus system further comprises a housing for supporting the rotor and the stator as well as a magnet for providing a magnetic field in the vicinity of the at least one brush. 
     The present invention also involves a test system, comprising an apparatus for testing a plurality of brushes and a plurality of brush holders under a varying magnetic field. The test apparatus comprises a stator, at least one brush holder coupled to the stator, at least one brush held by the at least one brush holder, a rotor positioned to contact the at least one brush, a drive shaft coupled to the rotor, and a magnet for supplying a magnetic field, wherein the at least one brush contacts the rotor. The test apparatus system further comprises a drive system coupled to the drive shaft, a power supply for providing power to the at least one brush, and a power supply for providing power to the magnet. 
     Another subsequent embodiment can be characterized as a method of testing at least one brush and at least one brush holder, the method comprising rotating a rotor of a test apparatus, providing power from a brush power supply to at least one brush in contact with the rotor, providing power from a magnet power supply to a magnet, and generating a magnetic field from the magnet in the vicinity of the at least one brush and the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. 
         FIG. 1  is a front perspective diagram of a test apparatus, in accordance with an embodiment of the present invention. 
         FIG. 2  is a rear perspective diagram of the test apparatus, as shown in  FIG. 1 , in accordance with an embodiment of the present invention. 
         FIG. 3  is a front view diagram of the test apparatus, shown in  FIG. 1 , in accordance with an embodiment of the present invention. 
         FIG. 4  is a side cross-sectional diagram of the test apparatus, as shown in  FIG. 1 , in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of a test system, comprising a test apparatus, in accordance with an embodiment of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions, sizing, and/or relative placement of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Also understood is that the terms and expressions used herein have the ordinary meanings as are usually accorded to such terms and expressions by those skilled in the corresponding respective areas of inquiry and study, except where other specific meanings have otherwise been herein set forth. 
     DETAILED DESCRIPTION 
     The following description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the herein appended claims. The present embodiments address the problems described in the background while also addressing other additional problems as will be seen from the following detailed description. 
     The embodiments described herein provide an apparatus for testing brushes in a variety of different conditions. The brushes can be subjected to a magnetic field, such as would be present in real-world applications. Because the brushes of homopolar machines can be the greatest source of failure, the capability of testing various brushes under a variety of different conditions is advantageous. Additionally, some embodiments provide the ability to test and measure the brush performance under many different environmental situations. The long term evaluation of brushes under typical motor operating conditions can be monitored in order to improve wear rate, current density, efficiency, and reliability. Additionally, the interactions between the brushes and the rotor contact surface can be evaluated. 
     Advantageously, in some embodiments, both magnetic field components (B r  and  13   z ) can be adjusted in the vicinity of the brushes and brush holders. In various embodiments, the brushes can be evaluated over a large variation in the disc surface speed. Additionally, the brushes can be evaluated with different additives at the interface between the brush and the rotor. The brushes can also be evaluated for losses due to Ohmic heating resulting from transfer and circulating currents, as well as for mechanical losses resulting from friction. The long term performance of the brushes can be evaluated based upon the azimuthal location of the brush and holder as well as the effect of wear due to particle accumulation in long term performance. 
     Advantageously, the evaluation of the brushes under different ranges of coverage factors can be performed. Additionally, the thermal limits and operational envelope of the brushes and the brush holders can be evaluated. Different brush designs and the evaluation of brushes under different duty cycles can be evaluated. The validation of parameters from both a microscopic analysis and a macroscopic analysis as well as modeling can be performed. Furthermore, the accumulation of data to support statistical analysis for the projection of a lifetime for the brushes can be accomplished for a large number of brushes. Advantageously, the test apparatus, in some embodiments, can be operated unattended, twenty-four hours per day, for extended periods of time. 
     The above features can be accomplished in various embodiments of the apparatus described herein. The following description of a test apparatus, system, and method in accordance with various embodiments will further describe and detail the above features. 
     Referring now to  FIG. 1 , a front perspective diagram illustrates a test apparatus  100 , in accordance with an embodiment of the present invention. Shown is a rotor  102 , a stator  104 , a set of brushes  106 , a brush holder  108 , a machine housing  110 , a support structure  112 , a drive system  114 , a plurality of gas delivery tubes  116 , a plurality of connectors for a data acquisition system  118 , a plurality of power supply connectors  120 , a magnet power supply connector  122 , a cryo-cooler, e.g., a cryo-compressor  124 , an environmental chamber housing  126 , a support ring  128 , and a plurality of attachment clips  130 , by example only. An environmental delivery system supplies gas to the environmental chamber  126 . The plurality of power supply connectors  120  comprises first and second power supply connectors. 
     The brush holder  108  is connected to the stator  104  and holds the brushes  106  in contact with the rotor  102 . The rotor  102  and stator  104  are held in place by the machine housing  110  and the support structure  112 . This embodiment includes only one brush holder  108 ; however, a plurality of brush holders can be connected to the stator  104 . The plurality of gas delivery tubes  116  are coupled to the brush holders and supply gas, e.g., carbon dioxide, that controls the pressure that the brushes  106  exert in contacting the rotor  102 . In this embodiment, the apparatus comprises two brushes  106  and one brush holder  108 ; however, understood is that many brushes and brush holders may be placed around the stator in other embodiments. Additionally, the brushes and brush holders are placed on both an inner side and an outer side of the stator in some embodiments (see  FIG. 4 ). The present test apparatus is capable of testing up to one hundred twenty brushes at one time. In order to hold one hundred twenty brushes, twenty brush holders are disposed on the outside of the stator  104 ; and twenty brush holders are disposed on the inside of the stator  104  (see  FIG. 4 ). Each brush holder can be configured to hold a plurality of brushes. Thus, in the embodiment shown, when the test apparatus  100  is fully loaded,  120  brushes are being tested simultaneously. 
     The plurality of power supply connectors  120  are generally coupled to a power supply (not shown). The power supply supplies power to the test apparatus and controls the current flowing from the stator, through the brushes, and into the rotor. The drive system  114  (shown in more detail in  FIG. 3 ) is used to rotate the rotor  102  as current flows through the brushes  106 . Additionally, a magnetic field is produced by a magnet (shown in  FIG. 4 ) such that the brushes  106  are subjected to a magnetic field. The magnetic field simulates the environment to which the brushes would be subjected in a motor in operation. The magnet, which can produce magnetic fields over a range of strengths, is powered by a magnet power supply. The magnet power supply is coupled to the magnet through the magnet power supply connector  122 . The cryo-cooler, e.g., cryo-compressor  124  cools the magnet. In one embodiment, the magnet is a super-conducting magnet that operates at approximately 4.2 degrees Kelvin. The magnet produces a magnetic field when charged by the power supply. The strength of the field varies depending upon the level of charge of the magnet. In one embodiment, the proportion of the axial and radial portions of the magnetic filed (B z  and B r ) in the brush operating region are controlled by varying the charge of the magnet and by adjusting the axial position of the rotor  102  and brushes  106  relative to the magnet. 
     The environmental chamber housing  126  is attached to the front of the machine housing. The environmental chamber housing  126  encloses the rotor  102 , the stator  104 , and the brushes  106  inside of an environmentally controlled chamber. The environmental chamber housing  126  comprises, in the exemplary embodiment, the support ring  128 , the plurality of attachment clips  130 , and a front plate. The front plate is made from, for example, glass or plastic, and is preferably light transmissive, such that the brushes can be viewed during operation. The environmental chamber housing  126  allows for the brushes to be tested under a variety of different environmental conditions, such as with different temperatures and different gasses. Because the front plate is generally made from a transmissive material, it is not shown in the figure; however, the front plate forms a seal on the inside of the support ring. 
     Referring to  FIG. 2 , a rear perspective diagram illustrates a test apparatus, as shown in  FIG. 1 , in accordance with an embodiment of the present invention. Shown is the machine housing  110 , the support structure  112 , the drive system  114 , the plurality of connectors for the data acquisition system  118 , the plurality of power supply connectors  120 , the magnet power supply connector  122 , the cryo-cooler, e.g., a cryo-compressor  124 , a drive belt  132 , a drive shaft  134 , and a water union  136 . 
     The drive system  114  is coupled to the drive shaft  134  through the drive belt  132 . The drive system  114  rotates the drive shaft  134  of the test apparatus  100  in a controlled manner. The drive system  114 , in one embodiment, is a variable frequency controlled electric motor and drive belt system that can produce a rotor speed of up to 30 m/s. Because the test apparatus  100  includes the drive shaft  134  and, additionally, the magnet, the test apparatus is not a true motor. As described above, the magnets are charged as the rotor  102  is rotated and current is driven through the brushes  106 . This creates torque which must be compensated by the drive system  114 . Thus, a balance exists between the drive system  114  and the magnet that is taken into account when operating the test apparatus  100 . Generally, in a motor, the rotor has many windings that create a large amount of torque; however, the present embodiment of the test apparatus  100  only includes one winding, thereby reducing the generated torque. 
     As described, in one embodiment, the drive system  114  is a variable frequency drive (VFD) that is used to control the speed of the rotor  102 . The VFD controls the speed of the motor that, in turn, drives the rotor  102 . In operation, the VFD will maintain a constant revolutions per minute (RPM) of the rotor. The current passing through the brushes and rotor  102  in the magnetic field generated by the magnet will either add torque or reduce torque on the rotor  102 , i.e., either try to accelerate the rotor or brake the rotor. If the current is trying to accelerate the rotor  102 , the VFD must provide braking torque to maintain a constant RPM of the rotor. If the current is trying to decelerate the rotor, the VFD will provide additional torque to maintain the constant RPM of the rotor. In one embodiment, the VFD is a commercially available unit with an internal chopper to allow dissipation of braking energy. The energy is dissipated into an external, water cooled, braking resistor. The VFD settings may be made at the front panel of the VFD or remotely via an Ethernet port. The Ethernet port also allows for remote monitoring of the status of the VFD. 
     A water cooling system is connected to the water union  136 . The water cooling system is a controllable cooling system for the rotor  102  and stator  104 . This allows the brushes to be tested at varying degrees of operation and also prevents the rotor  102  and the stator  104  from overheating. Water is supplied to the water union  136  through water hoses (not shown). The water union  136  is designed such that the drive shaft  134  can rotate while the water union  136  remains in place. In one embodiment, the water union  136  is a hydraulic rotary union mounted to the end of the drive shaft  134  which passes water down holes in the drive shaft  134  and into the slip rings. Supply and return hoses from the cooling water system connect to the hydraulic rotary union and also to plumbing connected to the stator bus bars. 
     Referring to  FIG. 3 , a front view diagram illustrates the test apparatus, as shown in  FIG. 1 , in accordance with an embodiment of the present invention. Shown are the rotor  102 , the stator  104 , the brushes  106 , the brush holder  108 , the support structure  112 , the plurality of gas delivery tubes  116 , and the environmental chamber housing  126 . 
     The stator  104  is divided into four sections. Each section can hold up to five brush holders. The plurality of gas delivery tubes  116  supply gases to a respective plurality of brush holders, thereby controlling the pressure that the brushes  106  exert on the rotor  102 . In one embodiment, the rotor  102  is an electrically-shorted double slip ring mounted onto a stainless steal wheel and shaft. Each section of the stator  104  comprises two stacked copper bus bars mounted to a back plate (shown in  FIG. 4 ). 
     Referring to  FIG. 4 , a cross-sectional diagram illustrates the test apparatus, as shown in  FIG. 1 , in accordance with an embodiment of the present invention. Shown is the rotor  102 , the stator  104 , a first brush  140 , a second brush  142 , a first brush holder  144 , a second brush holder  146 , a first bus bar  147 , a second bus bar  148 , a back plate  150 , the machine housing  110 , the support structure  112 , the drive system  114 , the drive belt  132 , the plurality of gas delivery tubes  116 , a magnet  152 , a magnet housing  154 , the drive shaft  134 , the water union  136 , a first bearing  155 , a second bearing  156 , a center chamber  158 , a gas delivery attachment  150 , and the environmental chamber housing  126 . 
     The first brush  140  is held by the first brush holder  144 ; and the second brush  142  is held by the second brush holder  146 . The first brush holder  144  is connected to the first bus bar  147  on a front side of the stator  104 ; and the second brush holder is connected to the second bus bar  148  on a back side of the stator  104 . As described above, the brush holders  142 ,  144  can be attached to either the front side or the back side of the stator  104 , thus allowing for greater capacity to test the brushes  106 . 
     The center chamber  158  and the gas delivery attachment  160  allow for the delivery of environmental gases into vicinity of the brushes  106 , the rotor  102 , and the stator  104 . The environmental chamber housing  126  (described above in relation to  FIG. 1 ), disposed on the front of the test apparatus  100 , maintains the gas at the front of the test apparatus  100 . This allows the brushes  106  to be tested while in the presence of different types of environmental gases and varies pressure within the chamber  158 . The environmental chamber housing  126 , in one embodiment, encloses the stator  104 , the rotor  102 , and the brushes  106 . The environmental chamber housing  126  is sealed and various gaseous atmospheres, as delivered by an environmental control system, can be tested. 
     The magnet housing  154 , in one embodiment, is a vacuum-sealed, super-cooling chamber for a superconducting magnet. The superconducting magnet is cooled by the cyro-compressor  124 . The superconducting magnet can generate large magnetic fields in the vicinity of the brushes  106 , thus allowing for the testing of the brushes  106  under conditions that simulate the real operation of motors. 
     The drive shaft  134  is supported by the first bearing  154  and the second bearing  156 . In one embodiment, the first bearing  154  and the second bearing  156  are rolling element bearings. The bearings  154 ,  156  allow the drive shaft  134  to easily rotate. The drive shaft  134  is coupled to the rotor  102 , thus as the drive motor is on the drive belt  132  rotates the drive shaft  134  which in turn rotates the rotor  102 . Additionally, during operation, the magnet  152  generates a magnetic field in the vicinity of the first brush  140  and the second brush  142 . The rotor  102 , the stator  104 , and the brushes can be adjusted in an axial direction of the shaft by adjusting the position of the drive shaft  134 . That is, the relative axial position of the brushes  106  in relation to the magnet  152  is adjustable. This adjustment allows for control over both the axial and radial components of the magnetic field (B z  and B r ) in the vicinity of the brushes  106 , thus allowing for a more controlled environment for testing. 
     The stator  104  is connected to the back plate  150  which is mounted to the machine housing  110 . The first bus bar  147  and the second bus bar  148  can be easily accessed and allow for the relatively simple removal and replacement of the brush holders  144 ,  146  and/or brushes  106 . As described above, in one embodiment, the stator  104  comprises four sections where each section includes two stacked bus bars mounted to the back plate  150 . The bus bars line up with the two rings of the double copper slip ring of the rotor  102 . The brush holders  144 ,  146  are mounted to the bus bars and the brushes  106  are then in contact with the rotor slip rings. The two bus bars are electrically isolated from each other and from the back plate  150 . 
     Referring to  FIG. 5 , a schematic diagram illustrates a test system, in accordance with an embodiment of the present invention. Shown is a test apparatus  500 , a control system  502 , a brush power supply  504 , a cyro-cooler  506 , a cooling system or chiller  508 , a magnet power supply  510 , and a data acquisition system  512 , a gas supply system  514 , an environmental control system  516 , and a drive motor  518 . 
     The control system  502 , in one embodiment, controls the operation of the entire system, including the test apparatus  500 , the magnet power supply  510 , the brush power supply  504 , the chiller  508 , the environmental control system  516 , the cyro-cooler  506 , the gas supply system  514 , and the data acquisition system  512 . In an alternative embodiment, at least one or more of the individual components of the system are operated independently of the control system  502 . For example, the data acquisition system  512  can be operated independently from the control system  502 . The brush power supply  504  is connected to the test apparatus  500  and supplies current to the brushes  106 . the rotor  102 , and the stator  104  during operation. In one embodiment, the brush power supply  504  is a constant-current supply used to provide the current for testing the brushes  106 . The brush power supply  504  is capable of providing up to 6,000 amps dc at up to 5 volts. The brush supply is a low ripple supply (&lt;1% pk-pk of full current) even at low voltage. The brush power supply  504  consists of two commercial supplies, each rated at 3,000 amps, bused together in parallel. “Freewheeling” diodes provide protection for the brush power supply  504  from the back EMF that can be generated by the movement of the rotor  102  in the magnetic field. The brush power supply  504  utilizes a master-slave configuration where the master settings are used to control both supplies. A DC power supply capable of delivering up to 26,000 Amps at 10 Volts may be connected to the stator bus bars. The current path delivered by the brush power supply  504  is through one stator bus bar, through the brush holders  144 ,  146  and brushes  106  into the rotor slip ring, through the rotor  102  into the second slip ring, and out of the second slip ring through brushes  106  and brush holders  144 ,  146  mounted to the second bus bar. 
     The magnet power supply  510  supplies power to the magnet during operation in order to induce a magnetic field in the vicinity of the brushes  106 . The cyro-cooler  506  cools the magnet during operation. As described above, in one embodiment, the magnet is a superconducting magnet that is cooled to 4.2 degrees Kelvin. The gas supply system  514  provides gas to the brush holders  144 ,  146  which, in turn, control the pressure that the brushes  106  exert on the rotor  102 . The chiller  508  provides cooling for the rotor  102  and stator  104  during operation. The drive motor  518  is, for example, a variable frequency motor that is coupled to the shaft through a drive belt. The drive motor  518  turns the shaft which then turns the rotor  102  during operation. 
     The environmental control system  516  supplies environmental gases to the environmental chamber of the test apparatus  500 . This allows the brushes  106  to be tested under different pressure and environmental conditions. The data acquisition system  512  is connected to the test apparatus  500  and collects data about the temperature and pressure, e.g., temperature data and pressure data, within the environmental chamber of the test apparatus  500 . The data acquisition system  512 , in one embodiment, is a standard system including sensors and data logging equipment, such as, a computer system. The data acquisition system  512 , in one embodiment, is connected to sensors designed to measure temperature, voltage drop, brush wear, humidity, oxygen concentration, pressure, speed, and many other parameters at various points. In particular, stator bus bar, brush holder  144 ,  146 , brush  106 , and rotor slip ring temperatures are measured. In one embodiment, up to 175 channels are allocated for instrumentation with the majority of the measurement signals being recorded on by the data acquisition system  512 . 
     Information as herein shown and described in detail is fully capable of attaining the above-described object of the invention, the presently preferred embodiment of the invention, and is, thus, representative of the subject matter which is broadly contemplated by the present invention. The scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and is to be limited, accordingly, by nothing other than the appended claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment and additional embodiments that are known to those of ordinary skill in the art are hereby expressly incorporated by reference and are intended to be encompassed by the present claims. 
     Moreover, no requirement exists for a device or method to address each and every problem sought to be resolved by the present invention, for such to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. However, that various changes and modifications in form, material, and fabrication material detail may be made, without departing from the spirit and scope of the invention as set forth in the appended claims, should be readily apparent to those of ordinary skill in the art.