Abstract:
A fractional boost system including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a fractional boost system and more particularly to such a fractional boost system adapted for operating motors and motor drives especially in mobile robots. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally mobile robots are desired to be as light and inexpensive as permissible. One source of weight and cost are the one or more motors and motor drives that operate the robot. One way to reduce the size and cost of the motors and drives is to use motors with increased voltage and hence lower current ratings. One problem with this is that the higher voltage motors require higher voltage batteries which are less reliable and are more difficult to charge. Further, in many applications the power supply voltages are already standardized at some level e.g. 36 volts. Another approach is to choose higher voltage motors, but utilize field weakening of the motors so that at high speeds they don&#39;t need the high voltages but these controllers are not commercially, freely, available and some classes of motors cannot be sufficiently field weakened to obtain worthwhile results. Further, on failure the voltage can return to high voltage which can damage the electronic controls and battery. Another approach is to simply add a full boost converter to obtain a higher voltage intermediate bus commensurate with the higher voltage rated motor. However, this requires a second power supply or DC/DC converter able to supply the full rated voltage and current which adds substantial size, weight and cost. 
       SUMMARY OF THE INVENTION 
       [0003]    It is therefore an object of this invention to provide an improved motor drive with a fractional boost system. 
         [0004]    It is a further object of this invention to provide such an improved fractional boost system which is smaller, lighter, more efficient and less costly. 
         [0005]    It is a further object of this invention to provide such an improved fractional boost system for use with motors and motor drives. 
         [0006]    It is a further object of this invention to provide such an improved fractional boost system which allows for lower cost, lower size and weight motor and motor drives. 
         [0007]    It is a further object of this invention to provide such an improved fractional boost system which permits high speed operation and low current operation of a motor while preserving high torque operation at low speed. 
         [0008]    It is a further object of this invention to provide such an improved fractional boost system which eliminates the need for high voltage batteries. 
         [0009]    It is a further object of this invention to provide such an improved fractional boost system which adds only the minimum required amount of power conversion. 
         [0010]    It is a further object of this invention to provide such an improved fractional boost system which is fault tolerant, e.g. recovery of mobile robots even if there is a failure in the boost converter. 
         [0011]    It is a further object of this invention to provide such an improved fractional boost system which can provide a continuum of complementary torque/speed (current/voltage) ratios. 
         [0012]    It is a further object of this invention to provide such an improved fractional boost system which can be selectively enabled/disabled to improve efficiency. 
         [0013]    The invention results from the realization that in some cases full power, full voltage and current, are not needed at all times, indeed in some applications high voltage and high current are not needed simultaneously, that is operation at high speed (voltage) with high torque (current) is not a requirement and therefore a fractional boost system with much less size, weight and cost can work well by using a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current in the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. 
         [0014]    The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
         [0015]    This invention features a fractional boost system including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. 
         [0016]    In preferred embodiment the control system may disable the boost function of the boost converter when the current to the boost converter exceeds the predetermined level while enabling the boost converter to apply the power supply base level voltage and supply current exceeding the predetermined level to the load. The control system may limit the current to the boost converter to no more than the predetermined current level while providing additional current to the load from the power supply at the base level voltage. The control system may include a switch device in parallel with the boost converter for enabling current flow from the power supply only when the boost level voltage decreased below the base level voltage. The control system may include a current sensor for sensing the current to the boost converter and a first comparator for determining whether the current to the boost converter exceeds the predetermined level. The control system may include a voltage sensor for sensing the voltage at the load and a second comparator circuit for determining any difference between the voltage at the load and the boost level voltage. The control system may include a proportional integral derivative circuit responsive to the second comparator circuit for providing an output representative of any the difference between the voltage at the load and the boost level voltage. There may be a pulse width modulator responsive to the first and second comparator for setting the duty cycle of the boost converter. The load may include a motor drive. The load may include a number of motor drives. The motor drive(s) may be in a mobile robot. 
         [0017]    This invention also features a fractional boost system for a motor drive including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. 
         [0018]    This invention also features a fractional boost system operating one or more motor drives of a remote controlled mobile robot including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. 
         [0019]    This invention also features a fractional boost system for a motor drive including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. The control system disables the boost function of the boost converter when the current to the boost converter exceeds the predetermined level while enabling the boost converter to apply the power supply base level voltage and supply current exceeding the predetermined level to the load. 
         [0020]    This invention also features a fractional boost system operating one or more motor drives of a remote controlled mobile robot including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load. The control system limits the current to the boost converter to no more than the predetermined current level while providing additional current to the load from the power supply at the base level voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0022]      FIG. 1  is a diagrammatic view of a mobile robot employing a fractional boost system according to this invention to operate one or more motor drives and motors; 
           [0023]      FIG. 2  is a more detailed schematic diagram of the fractional boost system of  FIG. 1 ; 
           [0024]      FIG. 3  illustrates a number of voltage and current waveforms occurring in the fractional boost system of  FIG. 2 ; 
           [0025]      FIG. 4  illustrates speed and torque characteristics during different phases of operation of the motors drives by the fractional boost system of  FIG. 2 ; 
           [0026]      FIG. 5  is a more detailed schematic block diagram of the control system of  FIG. 2 ; 
           [0027]      FIG. 6  is a view similar to  FIG. 2  of another embodiment of a fractional boost system according to this invention; and 
           [0028]      FIG. 7  is a block diagram illustrating the fractional boost system of this invention operating a number of motor drives and motors. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0030]      FIG. 1  shows a mobile, remotely controlled robot  10  driven by tracks  12   a  and ( 12   b  not shown) in accordance with one particular example of a robot in accordance with the subject invention. Robot  10  includes a turret  14  which carries a fractional boost system  15  according to this invention which drives motor drive  16  which in turn drives motor  17 ,  18 ,  19 , and  20 . Turret  14  also includes arm assembly  22  having lower arm  24  and upper arm  26 . Lower arm  24  is able to pitch up and down but it does not turn. Upper arm  26  pitches with respect to lower arm  24  and is driven by a chain drive extending along lower arm  24 . End effector  32  rotates via wrist  34 . Motor  17  operates lower arm  24 ; motor  18  operates upper arm  26 ; motor  19  rotates wrist  34  and motor  20  operates end effector  32 . Operator control unit  40  is used to wirelessly control robot  10  as is known in the art. 
         [0031]    There is shown in  FIG. 2  a fractional boost system  15  according to this invention which includes a boost converter  50  adapted for connection to a power supply  52 , such as a battery, for example, which provides a base level voltage of e.g. 36 volts. Boost converter  50  includes an inductor  54  whose input end  56  is connected to the positive terminal  58  of power supply  52  at voltage V s  e.g. 36 volts. The output  60  of inductor  54  is connected to unidirectional switch  62  which may be simply a diode and also to chopping transistor  64 . Chopping transistor  64  is operated by control system  66 . The output of boost converter  50  is presented at capacitor  68  which provides the output to motor drive  16 . 
         [0032]    Control system  66  includes a current sensor  70  which senses the current to boost converter  50  and feeds that information back on line  72  to control system  66 . Control system  66  also includes a voltage sensor  74  which feeds back the voltage V c  sensed across capacitor  68  in motor drive  16  on line  76  to control system  66 . Boost converter  50  thus responds to the base level voltage e.g. 36 volts of power supply  52  and provides a boost level voltage e.g. 72 volts, V c , to the load or motor drive  16 . Normally at low loads, that is low torque and low current, the system operates in this boost level voltage mode wherein control system  66  selectively turns off transistor  64  allowing the voltage and magnetic field across inductor  54  to build up positive at input  56  negative at output  60 . Then control system  66  turns off transistor  64  ceasing the charging of inductor  54  and causing the magnetic field to collapse and induce a reverse voltage which is positive at output terminal  60  and negative at input terminal  56  to be applied to the anode of diode  62 . This turning on and off or chopping by transistor  64  continues unless the current to the boost converter exceeds a predetermined level as sensed by current sensor  70 . When that happens control system  66  turns off transistor  64  and leaves it off. Power supply  52  is now connected directly through inductor  54 , which is essentially zero impedance to d.c., through diode  62  to capacitor  68  and motor drive  16 . As soon as the voltage on capacitor  68  connected to the cathode of diode  62  drops below the voltage on the anode, which in this case is the power supply voltage plus V s , e.g. 36 volts, current begins to flow from the power supply  52  and can now exceed the current limit imposed by control system  66 , but at 36 volts. Diode  62  is sized approximately for the current of inductor  54 . 
         [0033]    Until the boost converter exceeds the predetermined limit, the system operates with control system  66  alternately turning on and turning off transistor  64 . However, in order to maintain the proper boost level voltage V c  on capacitor  68  in motor drive  16  the voltage sensor  74  feeds back its signal on line  76  to control system  66  to vary the duty cycle of transistor  64 . If that voltage V c  falls below the desired voltage, control system  66  will increase the on time of transistor  64 . If the voltage V c  goes above the boost level voltage, control system  66  will decrease the on time of transistor  64 . Boost converter  50  is shown simply schematically and its particular configuration is not a part of this invention as any boost converter can be used in its place. The combination of the current sensor  70  and feedback line  72  with control system  66  supervising the operation of the boost converter at higher voltage allows lower cost and lower size and weight motors and motor drives to be used. It also permits high speed operation and low current operation of a motor while preserving high torque operation at low speeds and it does this while eliminating the need for higher voltage batteries. It adds only the required amount of power conversion and no more. It is also fault tolerant as can be seen from  FIG. 2 : should control system  66  fail or transistor  64  fail, the battery still has a direct path through inductance  54  and diode  62  to supply capacitor  68  and motor drive  16 . With other boost converter topologies a bypass switch can be used. 
         [0034]    The operation of boost converter  50 ,  FIG. 2 , is demonstrated using the wave forms shown in  FIG. 3 , where the current I 1 ,  80  charges up,  82 , when transistor  64  is turned on and then discharges,  84 , when transistor  64  is turned off. This charging and discharging of inductance  54  is a function of the drive signal to transistor  64  shown at  86  where the positive  88  or on-time of transistor  64  coincides with the charging cycle  82  of inductance  54  and the off-time  90  begins the discharge of inductance  54  which occurs well before the onset of the next on time. The charging and discharging of inductance  54  in this way provides a current through I d ,  92 , through diode  62  in the form of a fast rising leading edge  94  and a more slowing falling lagging edge  96 . It is these pulses that charge capacitor  68  producing the boost level voltage V c , e.g. 72 volts, to motor drive  16 . V c  waveform  98  shows a fairly smooth but somewhat rippled characteristic due to the filtering effects of capacitor  68 . 
         [0035]    The tradeoff of speed for torque is illustrated in  FIG. 4 , where for a first period of time  100 , the end effector is being positioned with no real load on it. The speed  102  can be very high due to the boost level voltage being high while during that same period the torque requirement  104  is quite low. In the next period of time  106 , when the end effector and the arms are moving a heavy load, the torque is very high  108 , but the speed  110  can and should be quite low. Finally, in the third period  112 , after the load has been moved, the end effector is stowed, here again with a no-load or light-load condition the speed can be very high  114  while the torque  116  again will be low. 
         [0036]    Control system  66 ,  FIG. 5 , may include a first comparator  120 , which responds to the current feedback on line  72  and compares it to a preset current limit  122 , for example, 20 amps. When the current feedback on line  72  exceeds that current limit  122 , comparator  120  provides an output to pulse width modulator  124  to shut off transistor  64 . Up until that time the pulse width modulator operates transistor  64  as previously explained. Also up until that limit is reached the boost level voltage, V c , is maintained at the proper level e.g. 72 volts, by comparing the voltage feedback on line  76  with a boost level reference voltage  126  e.g. 72 volts and a second comparator  128  which may simply be a summing circuit as indicated. Any difference between the voltage feedback on line  76  and the boost level reference voltage  126  causes proportional integral derivative circuit  130  to provide a signal on line  132  to increase or decrease accordingly the pulse width of the gating signals provided by pulse width modulator  124  to the gate of transistor  64 . When the voltage feedback is higher than the boost level reference the proportional integral derivative circuit  130  input will be negative and the duty cycle will be decreased. When the voltage feedback signal is lower than the boost level reference the proportional integral derivative  130  circuit will be positive and the duty cycle will be increased. Proportional integral derivative circuits are well known and do not form a part of this invention. For further efficiency, pulse width modulator  124  may be shut down at any time via a user command on line  134  through OR GATE  136 . The actual current limit  122  need not be fixed but can be varied as indicated at  123 . Likewise the boost level reference voltage  126  need not be fixed but may be varied as indicated at  124 . This permits a continuum of complementary torque/speed (curve/voltage) ratios available to the system. 
         [0037]    In another embodiment of the fractional boost system  15   a  according to this invention, the boost converter  50   a ,  FIG. 6 , is not simply on or off. Here boost converter  50   a , which may includes in it control system  66   a , may operate, for example, to provide the boost level voltage, V c , at up to some predetermined current level. When that predetermined current level is exceeded control system  66   a  does not simply turn off boost converter  50   a , rather it leaves it on, still providing its level of current up to but not exceeding the predetermined level. As more and more current is demanded by the motor drive  16  the voltage output from boost converter  50   a  will drop. When it drops below the base level voltage of power supply  52 , then power supply  52  will begin providing additional current as required and its voltage e.g. 36 volts will now be the voltage output to motor drive  16 . This embodiment too is fault tolerant as can be seen by the fact that, even if boost converter  50   a  fails of its own accord or some external problems, power supply  52  would still be available through diode  62   a  to supply motor drive  16 . In practice this diode can be replaced by other components. 
         [0038]    While the fractional boost system  15  of  FIGS. 2 and 6  show but a single motor drive  16  this is not a limitation of the invention, for as shown in  FIG. 7 , fractional boost system  15  may provide a number of motor drives  16   a - d  each of which drives one of a plurality of motors  17 ,  18 ,  19 , and  20  so that the single fractional boost system  15  of  FIG. 1  can actually drive a plurality of motors drives  16  for a plurality of motors  17 ,  18 ,  19 ,  20 , for example. 
         [0039]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
         [0040]    In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
         [0041]    Other embodiments will occur to those skilled in the art and are within the following claims.