Patent Publication Number: US-2018041145-A1

Title: Comminuting machine drive system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/941,247 filed on Nov. 13, 2015 (now U.S. Pat. No. 9,793,832), which is a continuation of U.S. patent application Ser. No. 13/863,815 filed on Apr. 16, 2013 (now U.S. Pat. No. 9,186,684) and is a non-provisional of and claims the benefit of U.S. provisional patent application Ser. No. 61/624,614 filed on Apr. 16, 2012, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The exemplary embodiments generally relate to comminuting machines and, more particularly, to drive systems for comminuting machines. 
       2 . Brief Description of Related Developments 
     Generally comminuting machines, such as those used in the material handling industry, include a feed device for feeding comminuting feed material into, for example, a mill or shredded for breaking the comminuting feed material into smaller pieces. The shredder may have a disc rotor assembly that needs to be started and stopped periodically during operation of the comminuting machine. There is a desire to have starting and stopping of the disc rotor in a controlled fashion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the disclosed embodiment are explained in the following description, taken in connection with the accompanying drawings, wherein: 
         FIGS. 1A-1C  are schematic illustrations of a portion of comminuting machine in accordance with in accordance with aspects of the disclosed embodiment; 
         FIG. 2  is a schematic illustration of a portion of the comminuting machine of  FIGS. 1A-1C  in accordance with an aspect of the disclosed embodiment; 
         FIG. 3  is a schematic illustration of a portion of the comminuting machine of  FIGS. 1A-1C  in accordance with an aspect of the disclosed embodiment; 
         FIGS. 4A and 4B  are schematic illustrations of a portion of the comminuting machine of  FIGS. 1A-1C  in accordance with aspects of the disclosed embodiment; 
         FIG. 5  is a schematic illustration of a disc rotor drive system in accordance with an aspect of the disclosed embodiment; 
         FIG. 6  is a schematic illustration of a disc rotor drive system in accordance with an aspect of the disclosed embodiment; 
         FIG. 7  is a schematic illustration of a drive system in accordance with an aspect of the disclosed embodiment; and 
         FIG. 8  illustrates a flow diagram in accordance with an aspect of the disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT(s) 
       FIGS. 1A and 1B  illustrate portions of a comminuting machine  100  in accordance with the exemplary embodiment. Although the disclosed embodiment will be described with reference to the drawings, it should be understood that the disclosed embodiment can be embodied in many alternate forms. In addition, any suitable size, shape or type of elements or materials could be used. 
     In the exemplary embodiment, the comminuting machine  100  is configured as a hammer mill shredder for exemplary purposes only. It should be understood that the exemplary embodiments described herein may be applied to any suitable comminuting machine without departing from the scope of the exemplary embodiments. In this example, the comminuting machine  100  may be configured for “shredding” or otherwise breaking up any suitable comminuting feed materials such as for material management, reclamation or recycling purposes. For example, machine  100  may have features as described in United States Patent Application having Ser. No. 12/551,138 with filing date Aug. 31, 2009 and entitled “Comminuting Machine Containment System” which is hereby incorporated by reference herein in its entirety. By way of further example, machine  100  may have features as provided by Harris Shredder Division of Harris Corporation, for example, Harris Model HS-80115 Shredder or otherwise. Here the comminuting machine  100  may include a frame  100 F, a feed chute  110  that is fed by an infeed conveyor  1140 , a feed roll  120 , a shredder  130 , an outfeed conveyor  1130 , a containment system  140 C and one or more drive units (referred to generally as “components” of the comminuting machine). It is noted that in alternate aspects of the disclosed embodiment, the comminuting machine  100  may have any suitable configuration and components. The drive units may be configured for driving one or more components of the comminuting machine  100  as will be described in greater detail below. The frame  100 F is configured in any suitable manner for supporting the components of the comminuting machine  100 , such as those described herein. In one example, the frame  100 F may be mounted on, for example, a foundation or other suitable footing  1101  and the components may be mounted to the frame  100 F in any suitable manner, such as on platforms or other suitable mounting features disposed on the frame  100 F. The containment system  140 C is configured to minimize a number of projectiles or particles being ejected from the comminuting machine  100  and passing outside the containment system boundary substantially without interference to feeding and discharge from the comminuting machine  100  as will be described further below. 
     The feed chute  110  includes a base  110 B and side walls  110 S which in this example for a substantially U-shaped channel. The feed chute  110  may be mounted to the frame  100 F at any suitable angle for allowing comminuting feed material to slide down the substantially U-shaped channel of the feed chute  110  by, for example, gravity so that the comminuting feed material substantially contacts the feed roller  120 . In alternate aspects of the disclosed embodiment, the feed chute  110  may include a conveyor or any other suitable material transport for providing comminuting feed material to the feed roller. In still other aspects of the disclosed embodiment, the feed chute  110  may have any suitable shape for conveying comminuting feed material to the feed roller  120 . 
     Referring also to  FIG. 2 , in this exemplary embodiment the feed roller  120  is configured as a double feed roller with, for example, at least one hydraulic drive  240 . In alternate aspects of the disclosed embodiment, the feed roller  120  may be any suitable feed roller having any suitable drive. Here the feed roller  120  includes a frame  200  and feed rolls  210 A,  210 B rotatably mounted to the frame  200 . The frame  200  may comprise a yoke that is pivotally mounted to, for example, the feed chute  110  (or to any suitable location of the frame  100 F of the comminuting machine  100 ) so that the feed rolls  210 A,  210 B can be pivoted up and down (via for example a hydraulic cylinder or other suitable drive) about, for example, axis  101  relative to the feed chute  110  for grabbing comminuting feed material or to help crush the comminuting feed material. Each of the feed rolls  210 A,  210 B may include one or more drive wheels  220  connected to the drive  240  by any suitable transmission. In alternate aspects of the disclosed embodiment, each of the feed rolls  210 A,  210 B may have a respective drive for directly or indirectly (e.g. through a transmission) driving the feed rolls. The feed rolls  210 A,  210 B may be configured with protrusions or teeth that grab the comminuting feed material located on the feed chute  110  so that the comminuting feed material is fed into the shredder  130  as the feed rolls  210 A,  210 B are rotated. 
     Referring to  FIGS. 1A-1C, 3, 4A and 4B  the shredder includes housing  130 H, internal castings  400  and rotor  300 . The housing  130 H may include an upper housing portion  131  and a lower housing portion  132  configured to at least partially house internal castings  400  and rotor  300 . In one example, the upper housing portion  131  may be movable (e.g. pivotally mounted) relative to the lower housing portion  132 . Suitable drives may be connected to the housing  130 H for effecting movement of the upper housing portion  131  relative to the lower housing portion  132  for allowing access to, for example the internal casting  400  and  300 . In one example the housing portions  131 ,  132  may be constructed of welded steel but in alternate embodiments the housing may be constructed of any suitable material(s) and in any suitable manner, such as with fasteners or with a unitary one-piece construction. The housing  130 H includes an inlet  130 A configured to receive comminuting feed material from the feed roller  120  and an outlet  130 B configured to provide comminuted or shredded material (e.g. comminuting discharge material) to, for example, the outfeed conveyor  1130 . 
     The internal castings  400  may be constructed of, for example, any suitable material such as a work hardening material. The internal castings  400  may include circumferential grates  420 , side walls  421  and an anvil  350  that substantially form a drum in which the rotor  300  rotates. The drum includes an inlet  410  and an outlet  435 . The inlet is configured for accepting the comminuting feed material provided by the feed roller  120 . The outlet may include an outlet chute  430 C and a grate  430 . The circumferential grates  420  and outlet grate  430  include apertures of a predetermined size such that as the comminuting feed material is shredded, pieces of material that are smaller than the apertures fall through the circumferential grates  420  (e.g. bottom material discharge) or are discharged out of the grate  430  (e.g. top material discharge) for passage through the housing outlet  130 B. In one example, the internal castings  400  may also include a reject door configured to discharge unshreddable material from the shredder  130  before contacting the rotor  300 . The anvil  450  is configured to provide a cutting edge for the rotor  300  as the comminuting feed material enters the shredder  130 . It is noted that the configuration of the internal castings  400  and the drum formed thereby is exemplary only and in alternate embodiments the internal castings may have any suitable shape and configuration for allowing rotation of the rotor and the shredding of comminuting feed material as described herein. 
     The rotor  300  includes a shaft  340 , rotor discs  330  and hammers  320 . The rotor shaft  340  may be constructed of any suitable material and is suitably mounted to, for example, the shredder housing  130 H in any suitable manner. In one example, the rotor shaft  340  may be supported within the shredder  130  by self-aligning spherical roller bearings. The rotor discs  330  may be keyed to the shaft  340  so that the shaft and the discs  330  substantially rotate as a unit. The rotor discs  330  may be constructed of any suitable material such as, for example, a wear resistant material. Spacers (not shown) separate the rotor discs  330  from each other on the shaft. The rotor discs  330  on the end of the shaft  340  (e.g. the “end discs”) may include suitable wipers  350  for substantially preventing material accumulation between an internal wall of the shredder housing  130 H and the end discs. The hammers  320  may have any suitable shape and size and be constructed of any suitable material. The hammers  320  may be pivotally mounted to the rotor discs  330  such that the hammers  320  are allowed to swing independent of each other and relative to the rotor discs  330 . The rotor  300  may be rotated within the shredder by any suitable drive  360  at any suitable speed. As the rotor  300  is rotated the hammers  320  interact with the anvil  450  for shredding the comminuting feed material fed into the shredder  130 . It is noted that the hammers  320  may also interact with the one or more of the grates  420 ,  430  for shredding the material. As described above, as the comminuting feed material is shredded and reduced in size the grates  420 ,  430  allow the shredded material to pass into and through the outlet  130 B of the shredder  130 . 
     In one aspect of the exemplary embodiment, the containment system may also include a controller  661  which may be common with the controller operating the comminuting machine, or may be a separate controller that may be communicably linked to the machine controller (see for example  FIG. 1C ). The controller may be disposed at any suitable location(s) relative to the comminuting machine. In one example, the controller may be disposed at least partly within the operator station  1150 . In another example, the comminuting machine  1100  may include a remote controller or control stations disposed at other locations on the comminuting machine that work in conjunction with the controller  661  so that the comminuting machine and its components can be operation from any suitable operating position. In one example, the controller  661  may include any suitable programmable logic controller configured to operate the various components of the comminuting machine including but not limited to solenoid valves, proximity sensors and proximity switches. 
     Referring now to  FIG. 5 , there is shown a schematic illustration of a disc rotor drive system. Referring also to  FIG. 6 , there is shown a schematic illustration of a disc rotor drive system. Shredder system  130  has rotor  300  and rotor drive  360  ( FIG. 3 ). Rotor  300  has hammers  320  and discs  330  on shaft  340  and is shown surrounded, for example, by upper and lower grates  420 ,  430  ( FIGS. 4A, 4B, 5 ). Support bearings  710 ,  712  may have bearings within pillow blocks or other suitable bearing support for shaft  340 . One or more brakes  716 ,  718  may be provided where brakes  716 ,  718  may be electrically or hydraulically operated disc brakes or any other suitable friction brake configured to slow, stop or otherwise interrupt rotation of the shaft and rotor  300 . A drive motor  730  is shown coupled to rotor shaft  340  in any suitable manner such as by power transmission  732 . Here power transmission  732  may be any suitable transmission for transferring rotational power from the drive motor  730  to the rotor shaft  340 . In one aspect the power transmission  732  may be a coupling, for example, allowing for misalignment or as a universal drive shaft between the drive  360  and rotor  300 . Alternately, motor  730  may be coupled directly to shaft  340 . Power transmission  732  may further have a multi pinion gear drive or other suitable speed reduction or power transmission. Alternately, power transfer  732  may be an air clutch and gear box to a center drive, a dual pinion gear driven drive, variable speed drive or otherwise. Power transmission  732  may further have an automatic or user operable clutch, torque limiter or fluid or other suitable coupling. Power provided by motor  730  may, by way of example, be from approximately 750 HP to approximately 10,000 HP or otherwise where, for example, a slip-ring/wound rotor type motor or other suitable motor may be utilized. In the disclosed embodiment, a friction-less brake utilizing any suitable fixed or variable loads such as, for example, rheostats may be utilized as described with respect to shredder wound rotor motor drive  360 . Here primary load or rheostat  734  and secondary load or rheostat  736  are shown coupled to motor  730 , such as to a winding of the motor, where motor  730  is driven by power source  740 . The primary and secondary rheostats  734 ,  736  may be any suitable rheostats such as, for example, liquid or braking resistor rheostats. Here, power source  740 , primary  734  and secondary  736  rheostats may be controlled by controller  661 , manually by an operator or otherwise. The secondary rheostat  736  may be an external rheostat in that the secondary rheostat  736  may selectively be connected to motor drive  730 , for example, to be engaged only for braking and bringing the speed of the rotor to 40-50% of the operating speed prior to shut down or otherwise. The secondary rheostat  736  (and/or controls therefor) may be located on a common control panel with the primary rheostat  734  (and/or controls therefor), e.g., within the operator station  1150  ( FIG. 1C ). In other aspects the secondary rheostat  736  (and/or controls therefor) may be located remotely from the primary rheostat  734  such as outside the operator station  1150  at any suitable location of the comminuting machine  100 . The primary and secondary rheostats  734 ,  736  may be used in combination with each other and/or individually (e.g. selectively engaged/activated and/or where an engaged one of the rheostats bypasses a non-engaged/inactive one of the rheostats). Here, by way of example, at any suitable motor operating speed the motor  730  may be turned off and the standard disc brake  716 ,  718  may be engaged for final stop. Here, prior to engaging brakes  716 ,  718 , the combined load of primary rheostat  734  and secondary rheostat  736  may be used to decelerate rotor  300 . In the disclosed embodiment, the primary rheostat may be a liquid rheostat and the secondary rheostat  736  may be a braking resistor rheostat  736 . In one aspect, one or more of the primary and secondary rheostats  734 ,  736  may be a combination of fixed or variable resistors. 
     As can be seen in  FIG. 6 , the secondary rheostat  736  may be placed in line with the primary rheostat  734  such that a bypass contactor  738  allows the secondary rheostat to be bypassed. For example, secondary rheostat  736  may be a bank of three fixed or variable resistors having parallel contactors  738 . The contactors  738  may be closed, for example, during startup when the primary rheostat  734  is being utilized or during normal operation so that the additional resistance provided by the secondary rheostat is not used. During, for example, shutdown (e.g. braking of the motor  730 ) the primary rheostat  734  may be placed in a maximum resistance position and the bypass contactors  738  may be opened allowing the secondary resistance provided by the secondary rheostat  736  to be in line with the resistance provided by the primary rheostat  734 . Alternately, contactors  738  may not be provided, for example, where the secondary rheostat  736  may be a variable resistor that may be decreased to a short. 
     Although drive  360  has been described with respect to slip-ring/wound rotor type motor  730  and primary and secondary rheostats  734 ,  736 , in alternate aspects of the disclosed embodiments, any suitable motor  730  with corresponding primary and secondary loads may be provided where the primary and secondary loads may be electrical, mechanical or otherwise. For example, drive  360  may have a wound rotor motor with liquid rheostat and power factor correction capacitors. By way of further example, drive  360  may have a synchronous motor, for example, with a soft start. By way of further example, drive  360  may have an induction motor with any suitable controller as a soft-start. By way of further example, drive  360  may have a synchronous-induction motor with liquid rheostat and dc field excitation. Alternately, any suitable motor, primary and secondary load may be utilized. Here, drive  360  may utilize a slip ring wound rotor three phase motor  730  and appropriate rheostat  734 ,  736 . Here rheostat  734  may be provided to allow motor  730  to be tolerant of long starts by limiting the starting current and the combination of rheostats  734 ,  736  may be utilized for braking as described where rheostats  734 ,  736  may be liquid resistance rheostats that insert a resistance into the rotor circuit which may be gradually reduced to a short circuit at the end of the starting cycle. Motor  730  and rheostats  734 ,  736  may be as commercially available, for example, from General Electric, MKS, Teco-Westinghouse or otherwise. In alternate embodiments any suitable motor  730 , primary  734  and secondary  736  loads may be provided. 
     Referring now to  FIG. 7 , a portion of a drive system  860  is shown for driving the rotor  300  ( FIGS. 3 and 5 ). The drive system  860  may be substantially similar to that described above with respect to, e.g.,  FIG. 5  however, in this aspect the motor  830  may be controlled in any suitable manner by any suitable controller, such as controller  661 . In this aspect the controller  661  may be connected to the motor through a main circuit breaker  800  and contactor S 1  for selectively providing driving motive force to the motor. Here at least one selectably engageable load, such as rheostat  836 , is placed on the stator circuit  890  rather than providing an additional rheostat to the secondary circuit on the wound motors as described above. The Rheostat  836  may be substantially similar to one or more of rheostats  736 ,  736  described above. It is noted that while only one rheostat  836  is shown any suitable number of rheostats may be provided. Also, in this aspect the motor  830  may be any suitable multi-phase motor such as those described above while in other aspects the motor  830  may be a squirrel cage motor having a high starting torque. 
     Here the motor  830  may be, for example, a three phase motor but in other aspects the motor  830  may have any suitable number of phases. A reverse magnetic field may be created in the motor  830  stator MS and the lines of the three phase motor may be single phased to reduce the current peaks during the transition between phases. In one aspect the reverse field is connected through the rheostat  836  so that the voltage on the motor  830  stator MS circuit is reduced. In other aspects the reverse field may be connected to the motor  830  stator MS circuit in any suitable manner. In one aspect the actual voltage of the motor  830  stator MS may be adjusted by a saline concentration of the rheostat  836 , e.g., where the rheostat is a liquid resistance rheostat. In another aspect the actual voltage of the motor  830  stator MS may be adjusted manually by, for example, adjustment of rheostat electrodes or in any other suitable manner. As may be realized, the voltage on the motor  830  rotor MR may also be reduced. 
     As can be seen in  FIG. 7 , the rheostat  836  may be connected in parallel with the contactor S 1  for selectively providing a stopping resistance to the motor to effect frictionless braking of the comminuting rotor. The branch or phase lines on which the rheostat  836  is located may also include contactor S 2  (or the contactor S 2  may be part of the rheostat  836 ). The contactors S 1 , S 2  are controlled in any suitable manner such as by controller  661 , relays or any other suitable control for sequencing the contactors as will be described below to allow for the selectable engagement of the rheostat  836 . 
     As an example, during normal operation a main breaker  800  of the motor  830  is closed, the contactor S 1  is closed and the contactor S 2  (which is in line with rheostat  836 ) is open so that the rheostat  836  does not affect the motor  830  during normal operation. During braking of the motor  830  one or more phases of the motor  830  may be opened and closed in a predetermined sequence so that the branch lines BL 1 , BL 2 , BL 3  and BL 1 ′, BL 2 ′, BL 3 ′ are single phased as will be described below. In one aspect, contact S 1 A (of the contactor S 1 ) which is located on branch line BL 1  may be opened to single phase the branch lines ( FIG. 8 , Block  900 ) then the other two contacts S 1 B, S 1 C (of the contactor S 1 ) which are disposed respectively on branch lines BL 2 , BL 3  may be opened ( FIG. 8 , Block  910 ). 
     The controller  661  may control the contactor S 2  so that the rheostat  836  is connected between the controller  661  and the motor  830  ( FIG. 8 , Block  920 ). For example, the controller  661  may close contacts S 2 A, S 2 B (of the contactor S 2 ) to single phase the lines BL 3 ′, BL 2 ′, BL 1 ′ to/from the motor  830  so that two phases BL 3 ′, BL 2 ′ of the rheostat  836  at least in part introduce resistance to the motor  830  to provide frictionless braking. The remaining contactor S 2 C (of the contactor S 2 ) which is disposed on branch line BL 1 ′ may be closed so that the rheostat  836  provides frictionless braking forces in the motor  830  ( FIG. 8 , Block  930 ). As may be realized, the sequence of opening and closing the phases of the contactors S 1 , S 2  is exemplary and in other aspects the phases of the contactors S 1 , S 2  may be opened and closed in any suitable sequence. In other aspects the phases S 1 A, S 1 B, S 1 C of contactor S 1  may be opened substantially simultaneously while phases S 2 A, S 2 B, S 2 C of contactor S 2  may be closed substantially simultaneously. At any suitable RPM of the rotor  300  the main circuit breaker  800  may be opened so that the motor  830  and/or rotor  300  are allowed to coast to a stop and/or a friction brake  716 ,  718  ( FIG. 5 ) can be engaged to stop the motor  830  and/or rotor  300 . 
     In accordance with one or more aspects of the disclosed embodiment, a comminuting machine is provided having a frame having a comminuting rotor coupled to the frame. A rotary drive is coupled to the rotor, the rotary drive having a slip-ring motor having a winding. A primary rheostat and a secondary rheostat are coupled to the winding, the primary and secondary rheostat being selectively engaged together providing braking of the slip-ring motor. 
     In accordance with one or more aspects of the disclosed embodiment, the primary rheostat and secondary rheostat are coupled to the winding such that the secondary rheostat is in line with the primary rheostat to provide a compounded resistance to the slip-ring motor. 
     In accordance with one or more aspects of the disclosed embodiment, a bypass contactor couples the primary rheostat to the winding such that the secondary rheostat can be selectively engaged. 
     In accordance with one or more aspects of the disclosed embodiment, the bypass contactor includes one or more contacts that are opened to selectively engage the secondary rheostat for braking of the slip-ring motor. 
     In accordance with one or more aspects of the disclosed embodiment, the bypass contactor includes one or more contacts that are closed to selectively disengage the secondary rheostat during slip-ring motor startup and operation. 
     In accordance with one or more aspects of the disclosed embodiment, one or more of the primary and secondary rheostat comprises a liquid rheostat. 
     In accordance with one or more aspects of the disclosed embodiment, one or more of the primary and secondary rheostat comprises a resistor bank. 
     In accordance with one or more aspects of the disclosed embodiment, a comminuting machine includes a frame, a comminuting rotor coupled to the frame, a rotary drive coupled to the comminuting rotor, the rotary drive having motor, and a rheostat brake connected to the motor, the rheostat brake including a primary rheostat and a secondary rheostat disposed in line with the primary rheostat to provide a compounded resistance to the motor. 
     In accordance with one or more aspects of the disclosed embodiment, the secondary rheostat is selectively engaged to provide the compounded resistance. 
     In accordance with one or more aspects of the disclosed embodiment, a bypass contactor connects the primary rheostat to the motor such that the secondary rheostat can be selectively engaged. 
     In accordance with one or more aspects of the disclosed embodiment, the bypass contactor includes one or more contacts that are opened to selectively engage the secondary rheostat to provide the compounded resistance. 
     In accordance with one or more aspects of the disclosed embodiment, the bypass contactor includes one or more contacts that are closed to selectively disengage the secondary rheostat during motor startup and operation. 
     In accordance with one or more aspects of the disclosed embodiment, one or more of the primary and secondary rheostat comprises a liquid rheostat. 
     In accordance with one or more aspects of the disclosed embodiment, one or more of the primary and secondary rheostat comprises a resistor bank. 
     In accordance with one or more aspects of the disclosed embodiment, a comminuting machine includes a frame, a comminuting rotor coupled to the frame, and a rotary drive coupled to the rotor, the rotary drive including a controller, a multi-phase motor connected to the controller, a set of contactors disposed between the controller and the multi-phase motor for selectively providing driving motive force to the multi-phase motor, and at least one rheostat disposed between the controller and the multi-phase motor, in parallel with the first set of contactors, for selectively providing a stopping resistance to the multi-phase motor to effect frictionless braking of the comminuting rotor, wherein the controller is configured to operate the set of contactors and the at least one rheostat to single phase lines of the multi-phase motor for providing the stopping resistance. 
     In accordance with one or more aspects of the disclosed embodiment, the controller is configured to operate the set of contactors to single phase lines of the multi-phase motor to disengage the driving motive force to the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the controller is configured to operate the at least one rheostat to single phase lines of the multi-phase motor to provide the stopping resistance to the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the controller is configured such that the set of contactors is closed and contactors of the rheostat are open during operation of the comminuting rotor. 
     In accordance with one or more aspects of the disclosed embodiment, the set of contactors includes a contactor for each phase of the multi-phase motor and the controller is configured to control each contactor to open one phase of the multi-phase motor and then open the remaining phases of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one rheostat includes a contactor for each phase of the multi-phase motor and the controller is configured to control each contactor to close two phases of the multi-phase motor and then close a remaining phase of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one rheostat is disposed on a stator circuit of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, a comminuting machine includes a frame, a comminuting rotor coupled to the frame, and a rotary drive coupled to the rotor, the rotary drive including a multi-phase motor, a controller connected to the multi-phase motor, a first set of contactors disposed in the connection between the multi-phase motor and the controller such that each phase of the multi-phase motor includes a respective contactor, a second set of contactors disposed in the connection between the multi-phase motor and the controller in parallel with the first set of contactors such that each phase of the multi-phase motor includes a respective contactor, where the first set of contactors and the second set of contactors are selectably engageable, and a load disposed on each phase of the multi-phase motor in-line with a respective one of the second set of contactors, wherein the controller is configured to open each contactor in the first set of contactors in a first predetermined sequence and close each contactor in the second set of contactors in second predetermined sequence to provide frictionless braking of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the multi-phase motor is a three phase motor, the first predetermined sequence is open a contactor on one phase and then substantially simultaneously open contactors on remaining phases, and the second predetermined sequence is substantially simultaneously close contactors on two phases and then close a contactor on a remaining phase. 
     In accordance with one or more aspects of the disclosed embodiment, the controller is configured to open the first set of contactors prior to closing the second set of contactors to provide the frictionless braking of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the load is at least one rheostat. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one rheostat is disposed on a stator circuit of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, a method for providing frictionless braking of a comminuting rotor of a comminuting machine where the comminuting rotor is driven by a multi-phase motor is provided. The method includes controlling, with a controller of the comminuting machine, a set of contactors disposed between the controller and the multi-phase motor where the set of contactors selectively provide driving motive force to the multi-phase motor, and controlling, with the controller, at least one rheostat disposed between the controller and the multi-phase motor, in parallel with the set of contactors, for selectively providing a stopping resistance to the multi-phase motor to effect frictionless braking of the comminuting rotor, and operating, with the controller, the first and second set of contactors to single phase lines of the multi-phase motor for providing the stopping resistance to effect the frictionless braking of the comminuting rotor. 
     In accordance with one or more aspects of the disclosed embodiment, the set of contactors are operated by the controller to single phase lines of the multi-phase motor to disengage the driving motive force to the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one rheostat is operated by the controller to single phase lines of the multi-phase motor to provide the stopping resistance to the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the set of contactors is closed and contactors of the rheostat are open during comminuting operation of the comminuting rotor. 
     In accordance with one or more aspects of the disclosed embodiment, the set of contactors includes a contactor for each phase of the multi-phase motor and the method further includes controlling each contactor to open one phase of the multi-phase motor and then open the remaining phases of the multi-phase motor. 
     In accordance with one or more aspects of the disclosed embodiment, the at least one rheostat includes a contactor for each phase of the multi-phase motor and the method further includes controlling each contactor to close two phases of the multi-phase motor and then close a remaining phase of the multi-phase motor. 
     It should be understood that the foregoing description is only illustrative of the aspects of the disclosed embodiment. Various alternatives and modifications can be devised by those skilled in the art without departing from the aspects of the disclosed embodiment. Accordingly, the aspects of the disclosed embodiment are intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims. Further, the mere fact that different features are recited in mutually different dependent or independent claims does not indicate that a combination of these features cannot be advantageously used, such a combination remaining within the scope of the aspects of the invention.