Abstract:
The automated floor sander includes numerous devices and mechanisms to facilitate the task of the operator of the machine. The machine includes a variable speed drive mechanism, enabling the operator to select the desired travel speed over the surface in order to optimize results. Another feature is the automated sanding drum lifting and lowering mechanism, which automatically raises and lowers the drum if the travel speed of the machine respectively decreases or increases below or above a predetermined point. A manual mechanism for controlling drum height is also provided. Yet another feature is a novel mechanism for automatically centering the sanding belt on its tension roller, which mechanism greatly reduces wear and tear on the belt and friction in the system when the belt reaches one end of the tension roller. These mechanisms may be incorporated separately from one another or in combination in a single machine, as desired.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to powered machines adapted for refinishing floors and similar surfaces. More particularly, the present invention comprises an automated, self propelled drum-type floor sander or refinisher incorporating a variable speed drive, a mechanism for raising and lowering the drum by control of the operator or automatically according to the speed of the machine, and a novel sanding belt centering mechanism. The above features may be incorporated singly or in combination in a floor sanding or refinishing machine, as desired. While the various embodiments of the present invention are directed primarily to a drum type powered sanding machine for use on floors, it will be seen that it is not limited to such use, but may be incorporated in various types of walk behind or ride behind floor or surface refinishing and treatment mechanisms, as desired. 
     2. Description of the Related Art 
     A large number of powered floor sanders and polishers have been developed over the years, in order to facilitate such work. These powered devices universally include either a drum or a disc powered by an electric motor or other prime mover, and some form of controls for an operator of the machine. Many such devices are sufficiently large as to provide seating for the operator, either integrally with the sanding or refinishing mechanism or as ride behind mechanism with controls. 
     One problem with such powered devices is that they are prone to damaging the floor if the movement of the machine is not maintained uniformly and consistently over the surface. If the machine progresses too slowly, the sanding drum or disc will remove too much material in that area, resulting in a low spot in the floor. Various mechanisms have been developed to allow the operator to lift the drum, or at least to reduce its pressure on the underlying surface, but the operator must be sufficiently skilled so as to control the machine precisely to avoid gouging the floor with such manually controlled mechanisms. 
     Another problem with conventional machines is the lack of speed control for the machine. While many powered machines are known which provide propulsion of the machine in addition to power for the sanding drum, such machines generally do not facilitate ready control of the machine&#39;s travel speed over the surface, and may have only a single forward speed, a single reverse speed, and/or a neutral or off configuration. This can lead to the same problem noted above, i.e. excessive sanding of the surface in one spot or area due to the machine being stopped or traveling too slowly, or conversely, too rapid a speed over an area which requires additional work. 
     Yet another problem with conventional machines is the difficulty in keeping the sanding belt centered upon the drum. While various mechanisms are known, they generally rely upon auxiliary rollers near the opposite ends of an idler roller, but misalignment of the belt will often overpower this system. 
     Thus, an automated floor sander solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The automated floor sander incorporates a number of features adapted to facilitate the task of removing the old finish from a flooring surface. The various features or embodiments of the present invention may be incorporated in either walk behind type machines or larger ride on or ride behind machines, as desired. 
     One of the features of the present automated floor sander is its speed control mechanism which allows the operator to vary the travel speed of the machine over the surface, according to the need to spend more or less time in a given area of the floor. 
     The present machine may also incorporate a fully automated drum lifting and lowering control system which automatically raises the drum if the speed of the machine decreases below a predetermined point and which automatically lowers the drum if the speed of the machine increases beyond the predetermined point. The machine may also include a manually actuated mechanism for raising and lowering the drum, as desired. In addition to the above mechanisms, the present machine may also include a novel mechanism for automatically centering the sanding belt. 
     The relatively large and heavy sanding drum drive motor of the present machine may also be quickly and easily removed and reinstalled as desired, without need for specialized tools. This enables the motor and the remainder of the chassis and mechanism to be broken down for carriage up a flight of stairs, ladder, etc., without undue strain upon those persons carrying the device. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a left front perspective view of an automated floor sander according to the present invention, showing its general configuration. 
         FIG. 2  is a left side elevation view in partial section, showing further details thereof. 
         FIG. 3  is an exploded right rear perspective view of the chassis and sanding drum motor assembly of the device, showing details of the motor installation. 
         FIG. 4  is a right side elevation view in partial section, showing details of the drive wheel propulsion and wheel and axle assembly height adjustment mechanism. 
         FIG. 5  is a detailed perspective view of the wheel drive motor and axle assembly, showing its articulation for raising and lowering the wheels on the floor to lower and lift the sanding drum accordingly. 
         FIG. 6  is an exploded perspective view of the linear actuator motor controlling the lifting and lowering of the drive wheels. 
         FIG. 7A  is a rear elevation view in section of the control handle of the device, showing various details thereof. 
         FIG. 7B  is a side elevation view in section of the control handle of  FIG. 7A , showing further details of the mechanism. 
         FIG. 8A  is an electrical schematic drawing of the circuitry for operating the sanding drum drive motor and propulsion motor of the present machine. 
         FIG. 8B  is an electrical schematic drawing of the drive wheel lifting and lowering systems. 
         FIG. 9A  is a schematic view of the switch configuration when the drive wheels are in their lifted position, i.e. with the sanding drum lowered. 
         FIG. 9B  is a schematic view of the switch configuration when the drive wheels are in a neutral or central position, between their lifted and lowered positions. 
         FIG. 9C  is a schematic view of the switch configuration when the drive wheels are in their lowermost position, i.e. for lifting the sanding drum clear of the surface. 
         FIG. 10  is a detailed right rear perspective view in section of the sanding drum and its tensioner and lateral belt guide mechanism, showing details thereof. 
         FIG. 11  is a right side elevation view in section of the sanding belt tensioner and lateral belt guide mechanism, showing further details of its mechanism and operation. 
         FIG. 12  is a top plan view of the sanding belt tensioner, showing its pivotal attachment about the angularly and forwardly offset pivot shaft. 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention comprises an automated floor sander incorporating one or more of a series of features therewith. The floor sander may include a variable speed drive, a mechanism for raising and lowering the drum by control of the operator or automatically according to the speed of the machine, and/or a novel sanding belt centering mechanism. The various features may be incorporated in a walk behind type floor sander, or in ride-on floor sanders or floor sanders having ride-behind attachments. 
       FIG. 1  provides a left front perspective view of an exemplary walk behind type floor sander  10  incorporating the various features of the present invention, with  FIGS. 2 and 4  respectively providing left and right side views and  FIG. 3  illustrating the basic chassis of the device. The floor sander  10  includes a chassis  12 , which may be cast, welded up, or otherwise formed, preferably of aluminum or other relatively lightweight but durable metal material. The chassis  12  provides for the installation of a rotary, cylindrical sanding drum  14  and sanding belt tension roller  16  laterally across the forward end  18  thereof, with an endless sanding belt  20  extending about the sanding drum  14  and tension roller  16 . The sanding drum  14  is driven by a belt  22  ( FIG. 2 ), with the belt  22  in turn being driven by a laterally disposed sanding drum drive motor  24  removably mounted in the upper center of the chassis  12 . A front cover  26 , which may include a handle  28 , and side cover(s)  30  serving to guard the belt  22  and other components, are shown clearly in  FIG. 1 . 
     The sanding drum drive motor  24  is a relatively heavy and bulky component, which when combined with the rest of the floor sander  10  apparatus, results in a heavy and cumbersome piece of equipment. This is necessary in order to provide the weight on the forwardly disposed sanding drum for good abrasive action during operation, but results in the assembled device being very difficult to transport manually. Accordingly, the chassis  12  is configured for quick release of the drum drive motor  24  therefrom, as shown in  FIGS. 2 and 3 . The drum drive motor  24  includes laterally opposed pins  32   a ,  32   b  extending therefrom, which respectively engage a mating slot  34   a  and passage  34   b  in the chassis  12 . The passage  34   b  includes oblong entrance and exit sides, resulting in the passage being sloped upwardly from the outer surface to the opposite inner surface of the chassis wall through which it passes. This allows the motor securing pin  32   b  to be inserted into and removed from the passage  34   b  at an angle, with the opposite pin  32   a  lifting essentially straight upward from the slot  34   a  when removal of the motor  24  is desired. A quick release, over center latch  36 , or alternatively some other securing means (threaded bolt, etc.) wedges the motor  24  upwardly, with the resulting tension on the sanding drum drive belt  22  securing the motor  24  in place against the pressure of the latch  36 . When manual transport of the sander assembly  10  is required, e.g. up a flight of stairs or the like, the heavy motor  24  may be removed from the chassis  12  by releasing the quick release latch  36 , disconnecting the electrical connection, removing the loosened sanding drum drive belt  22  from the motor pulley, and lifting the motor  24  from its installed position in the chassis  12 . This permits the motor  24  and chassis  12  to be carried independently of one another, thereby greatly reducing the work required to transport the device manually. The motor  24  is quickly and easily installed in the chassis  12  by reversing the procedure described above, to ready the sander for use. 
     The chassis  12  further includes an internal duct  38 , which draws sanding dust from the drum  14  at the forward end  18  of the chassis to a chassis outlet  40  by means of a blower or fan  42  (shown in broken lines in  FIGS. 1 and 2 ). The outlet  40  is connected to a generally upwardly extending duct  44  which also serves as a support or attachment for the handle assembly  46 , generally as shown in  FIGS. 1 ,  2 , and  4 . The duct  44  is angled from the chassis outlet  40  at the left rear of the chassis  12  toward the rear center of the chassis and has a downwardly curving distal end, from which a removable dust collection bag or container  48  depends. 
     The sander  10  is supported by a rearwardly disposed castering wheel  50  and left and right side support and drive wheels  52   a  and  52   b . The support and drive wheels  52   a  and  52   b  are disposed upon opposite ends of a laterally disposed axle  54  and support the majority of the weight of the sander  10 , along with the sanding drum  14 .  FIG. 5  illustrates the basic support and drive wheel and axle assembly, comprising wheels  52   a ,  52   b  and axle  54 . The axle  54  includes a driven worm gear  56   a  which is driven by a drive worm gear  56   b , with the drive worm gear  56   b  in turn driven by a propulsion motor  58 . The gear assembly  56   a ,  56   b  is encased within a case or housing  60  (shown in broken lines in  FIG. 5 ) which affixes the motor  58  immovably to the axle  54  (excepting rotation of the axle). The two drive wheels  52   a ,  52   b  preferably include one-way clutches (not shown) within their hubs, in order to provide a differential effect when turning the machine  10 . It should be noted that the propulsion motor  58  drives the axle  54  and wheels  52   a ,  52   b  in a direction opposite the rotation of the sanding drum  14 . This is because the drum  14  provides sufficient friction and traction to propel the machine  10  over the underlying surface, with the motor  58 , axle  54 , and wheels  52   a ,  52   b  acting as a brake to prevent excessively rapid travel across the surface. 
     The propulsion motor  58  is also immovably affixed to an axle and propulsion motor support shaft  62 , which extends laterally across the chassis  12 . The opposite ends of the support shaft  62  are pivotally secured within the chassis  12 . The propulsion motor  58  is laterally offset toward one end or side of the pivoting support shaft  62 , with the opposite end of the support shaft being immovably affixed to an axle carrier  64  which in turn supports the end of the axle  54  adjacent the left side wheel. An axle and propulsion motor support arm  66  extends rearwardly from the propulsion motor  58  and its support shaft  62 , and is immovably affixed to those components. Thus, the entire support and drive axle and wheel assembly, comprising the two wheels  52   a ,  52   b ; the axle  54 ; the propulsion motor  58 ; the pivot shaft  62 ; the axle carrier  64 ; and the support arm  66 , form a rigid assembly which pivots arcuately about the lateral axis defined by the pivot shaft  62 . As the rearward end of the support arm  66  is raised and lowered (by mechanisms described below), the two drive wheels  52   a ,  52   b  are lowered and raised accordingly, thereby lifting and lowering the sanding drum  14  relative to the underlying surface. Lateral adjustment for leveling the sanding drum  14  relative to the underlying surface is provided by a drive wheel leveling mechanism  68 , the left end of which may be seen in  FIGS. 1 and 2 . Briefly, a threaded bolt passes through the left end of the axle and motor support shaft  62 , to adjustably raise or lower that end of the shaft  62  as required. 
     The relative height of the drive wheels  52   a ,  52   b  may be adjusted either manually by a mechanical linkage, or electrically by means of a manually controlled switch or mechanism, or an automatic system. The rearward actuation end  70  of the axle and motor support arm  66  includes attachments for a manually actuated mechanical link  72  and an electric motor driven link  74 . 
     The control for the manually operated mechanical link  72  is illustrated in  FIG. 7A . The distal, upper operator control end  76  of the handle assembly  46  has an articulated handle extension  78  extending therefrom, pivoting on a lateral pivot  80  passing through the operator control end  76  of the handle assembly. A pair of opposed, relatively fixed hand grips  82  extends laterally from the handle extension  78 , with a manual drive wheel positioning lever  84  also extending laterally from the handle extension  78 , adjacent one of the fixed hand grips  82 . This lever  84  is secured to a pivot  86  within the handle extension  78 , with the upper end of the manual link  72  being pivotally attached to the lever  84 . The lever  84  may be moved manually to its raised position, shown in solid lines in  FIG. 7A , during operation of the machine. This raises the rearward actuation end of the axle and motor support lever arm  66 , as shown in  FIG. 5 , thereby pivoting the motor, axle, and drive wheel assembly about the lateral support shaft  62  and causing the axle  54  and drive wheels  52   a ,  52   b  to lower further, thereby lifting the sanding drum  14  clear of the underlying surface. The lever  84  may be unlatched from its raised position by releasing a rearwardly disposed latch button  88  to move a spring loaded catch  90  forwardly out of the plane of a tang  92  attached to the lever  84 , thereby allowing the lever  84  to drop to its lowered position (shown in broken lines in  FIG. 7A ). 
     The wheel assembly shown in  FIG. 5  may also be adjusted upwardly and downwardly by means of an electrically powered system, if so desired. A drive wheel lifting and lowering motor  94  and circuit boards  96  and  122  for the two motors  58  and  94  are installed in a housing  98  on the chassis  10 , adjacent the lower chassis attachment end  100  of the handle assembly  46 . (The lower end  100  of the handle assembly  46  is actually welded to the lower portion of the dust collector tube  44 , which is in turn rigidly secured to the chassis  10 .) The drive wheel lifting and lowering motor  94  is shown in  FIGS. 4 and 6 , with  FIG. 6  providing the greatest detail of the motor  94 , electronic control circuit boards  96 , the linear actuator  102  driven by the motor  94 , and the series of switches  104  through  112  actuated by the linear actuator. 
     The motor  94  rotates a threaded shaft  114 , which passes through the linear actuator  102 . The actuator  102  is restricted from rotation by a conventional keyed element, and thus is restricted to linear travel along the threaded shaft  114  as the motor  94  rotates one way or the other. As the actuator  102  travels along the shaft  114 , it also moves the link  74  to the drive wheel axle and motor support arm  66 , thus adjusting the drive wheels  52   a ,  52   b  upwardly or downwardly and correspondingly adjusting the sanding drum  14  downwardly or upwardly. In practice, the link  74  (and the mechanical link  72 ) are in tension, as the weight of the machine on the wheels tends to push the wheels upwardly, thereby drawing the actuation end  70  of the arm  66  downwardly. A supplementary tension spring  116  ( FIG. 4 ) attaches to the lateral extension  118  ( FIG. 5 ) of the support arm  66 . This spring  116  applies an upward force to the actuation end  70  of the axle and motor support arm  66 , thereby urging the wheels  52   a ,  52   b  downwardly to engage the underlying surface to provide traction when both the manual and powered or automated wheel lifting and lowering systems are lowered to allow the wheels to raise and the sanding drum  14  to lower. The tension of the spring  116  is adjustable to adjust the tractive force provided by the wheels accordingly. 
     The basic electrical operating system for the present machine is shown in  FIGS. 8A and 8B , with  FIG. 8A  illustrating the basic circuitry from the electrical connection (conventional plug, etc.) to the electrical power grid to the sanding drum drive motor  24  and propulsion motor  58 . The drum motor  24  is controlled by a double pole, double toggle switch  25 , with the propulsion motor being controlled by the second switch  125  adjacent to the master switch  124 . These switches are also shown on the side of the control box on the handle  46  in  FIGS. 1 and 2 . Electrical power continues from the circuitry of  FIG. 8A  to provide electrical power to the double pole, double throw master switch  124  shown in schematic of  FIG. 8B , and thence to the wheel lifting and lowering system and drive wheel control system shown generally in  FIG. 8B . 
       FIGS. 9A through 9C  illustrate the operation of the linear actuator  102 . The linear actuator includes a shoulder  120 , which moves along the pin plungers of the switches  104  through  112  as the actuator  102  is moved by the drive wheel lifting and lowering motor  94  to open and close those switches. 
     The first switches  104  and  106 , i.e. the leftmost two switches in  FIGS. 9A through 9C  and the lowermost two switches in  FIG. 6 , comprise the normally closed power switches which control electrical power to the actuator motor  94 . These two switches  104  and  106  may be in the form of one double pole switch having a single contact post, as shown, or two closely adjacent switches. A double pole switch is preferred, as the two switches  104  and  106  preferably act simultaneously to shut off and actuate power to the conventional DC motor control board  122  ( FIG. 8B ), and hence to the drive wheel lifting and lowering motor  94 , which also drives the linear actuator  102 . An on-off master toggle switch  124  is also provided on the control box installed on the handle  46 . This switch  124  is shown in  FIGS. 1 and 2 , and in the electrical schematic of  FIG. 8B . When the master switch  124  is closed, electrical power is provided to the double pole normally closed switch(es)  104  and  106 . Power is supplied from switch(es)  104  and  106  to the control board  122  to power the drive wheel and linear actuator motor  94  as required. 
     The third switch  108  is normally open, and is closed as the shoulder  120  rides over the pin plunger of the switch. This switch  108  controls power between the circuit board  122  and the high speed switching transistor  128  of the speed sensor  130 . The speed sensor  130  is a device which senses the travel speed of the machine  10  over the underlying surface, and automatically raises or lowers the drive wheels  52   a  and  52   b  by means of the linear actuator and wheel lifting and lowering motor  94  when the system is actuated. Speed sensing may be accomplished in various conventional ways, e.g. by sensing the electrical power drawn by the propulsion motor  58 , by a tachometer, by an optical encoder, etc. The manual drum latch switch  126  is located with the drum latch handle or manual wheel position lever  84  and latch assembly  86  through  90  of  FIG. 7A , although it is shown only in the electrical schematic of  FIG. 8B . 
     When the latch handle or lever  84  is lowered, The drum latch switch  126  is moved to complete the circuit to the momentary on contact switch  134  (see below) and thence to the common line of the third contact switch  110  when the contact switch  134  is actuated, thus allowing the drive wheels  52   a ,  52   b  to rise and allowing the sanding drum  14  to drop to the underlying surface (assuming adequate travel speed of the machine). In this configuration, wheel height control is accomplished by means of the previously noted high speed switching transistor  128  and its counterpart low speed switching transistor  132 , via the third through fifth linear actuator contact switches  108  through  112 . 
     When the latch handle or lever  84  is raised to lower the drive wheels  52   a ,  52   b , the drum latch switch  126  is switched to open the third contact switch circuit and close a circuit to a handle mounted pushbutton or momentary on toggle switch  134 . This switch  134  lowers the wheels  52   a ,  52   b , thus raising the sanding drum  14 , when it is pushed to close the circuit between the drum latch switch  126  and the fifth contact switch  112 . The pushbutton or toggle switch  134  normally closes the circuit between the drum latch switch  126  and the center pole of the fourth contact switch  110 , thus permitting automatic operation of the wheel and sanding drum height by means of the high and low speed switching transistors  128  and  132  of the speed sensor unit  130 . 
     As noted above, the present machine  10  includes circuitry which automatically raises and lowers the sanding drum  14  depending upon the travel speed of the machine over the underlying surface. This is accomplished by means of the speed sensor  130  and the low and high speed switching transistors  128  and  132 . When the machine is operating normally, the manual latch handle or wheel position lever  84  is lowered and the toggle or pushbutton switch  134  is released, thus closing the circuit between the third switch  110  and the linear actuator and motor controller  122  to the wheel lifting and lowering motor  94 . However, current draw is sensed by the high and low speed switching transistors  128  and  132  by means of the speed sensor  130 , with these transistors automatically opening and closing the circuits to the third through fifth switches  108  through  112  and thence to the motor controller  122  to control the linear actuator and wheel height control motor  94 . The speeds at which these switching transistors  128  and  132  are actuated may be adjusted as desired. 
     If the speed reaches too low a point, thus allowing the sanding drum to remain in one spot for too long a period, the low speed switching transistor  132  closes the circuit between the upper pole of the fourth switch  110  and the lower pole of the fifth switch  112 , thus actuating the motor  94  to drive the linear actuator from the lowered position shown in  FIG. 9A  to the center or neutral actuator position shown in  FIG. 9B , i.e. lowering the drive wheels  52   a ,  52   b  to raise the sanding drum  14 . 
     When the drive wheels have allowed the travel speed of the machine  10  to increase to a suitable point, the high speed switching transistor  128  senses this from the speed sensor  130  and closes the circuit between the third switch  108  and the center pole of the fourth switch  110 . This results in the linear actuator and wheel height position motor  94  moving the linear actuator  102  from the position shown in  FIG. 9B  back to the position shown in  FIG. 9A , thus raising the wheels  52   a ,  52   b  to lower the sanding drum  14  to the underlying surface. The above is accomplished completely automatically, so long as the master switch  124  is on, the drum latch handle or lever  84  is lowered to position the switch  126  properly, and the toggle or pushbutton switch  134  is released in order to close the appropriate portion of the circuit. 
     It will be realized that the above described mechanical linear actuator and switch series is but one means of accomplishing the switching functions for operating the wheel lifting and lowering mechanism. Other means may be used as well, while still remaining within the bounds of the present invention. For example, an optical system could be provided, with a series of optical detectors detecting the position of the linear actuator and operating the system accordingly. Infrared or magnetic means for detecting the position of the actuator could also be provided, if so desired. 
     A means of controlling the speed of the machine over the surface is provided by the articulating upper handle extension  78 , shown in  FIGS. 1 ,  2 ,  4 ,  7 A, and  7 B.  FIGS. 7A and 7B  illustrate the mechanical arrangement of the components, with the electrical schematic of  FIG. 8A  illustrating the speed control rheostat  136  in the circuit. (A separate rheostat or fixed value resistor  137 , shown in the electrical schematic of  FIG. 8B , is used to control the operating speed of the wheel lifting and lowering actuator motor  94 .) The handle extension  78  pivots forwardly and rearwardly on a pivot  80 , as described further above. A sector gear  138  extends downwardly from the pivot, and swings back and forth with motion of the handle extension  78 . The teeth of the sector gear  138  engage a pinion  140 , which in turn rotates the internal rotating component of the rheostat  136 . When the handle extension  78  is pulled rearwardly, the sector gear  138  swings forwardly, as indicated by the forward angle A 1 , which rotates the rheostat  136  counterclockwise (as shown in  FIG. 7B ) to decrease resistance to the circuit board  96  and increase the torque to the propulsion motor  58  driving the wheels  52   a ,  52   b . This slows the machine  10  due to the reversal of torque to the wheels  52   a ,  52   b  to compensate for the pull of the sanding drum  14  as it engages the underlying surface. When the handle extension  78  is pushed forwardly, the sector gear  138  swings rearwardly to rotate the rheostat  136  clockwise (in  FIG. 7B ), thus reducing resistance and reducing the torque of the propulsion motor  58  to reduce its rearward pull and allow the sanding drum  14  to drag or pull the machine  10  more rapidly over the surface. 
     A centering mechanism, most clearly shown in  FIG. 7B , is provided for the handle extension  78  in order to establish a neutral point for the rheostat  136  and resulting speed of the propulsion motor  58 . A centering arm  142  is affixed (welded, etc.) to the sector gear plate  138 , and terminates in a forked end  144  which fits over a stationary guide rod  146 . The rod  146  includes a larger diameter stop  148  (shown in broken lines within the fork  144 ) at its center. Centering springs  150   a  and  150   b  extend along the guide rod  146 , with stop washers  152   a ,  152   b  at their inboard ends. The springs  150   a ,  150   b  are prevented from extending beyond the center of the guide rod  146  by their stop washers  152   a ,  152   b  contacting the central stop  148 , thus providing a positive centering force for the arm  142  and the sector gear  138 . 
     The present automated floor sander machine  10  further includes a mechanism for automatically centering the sanding belt  20  upon the sanding drum  14  and tension roller  16 , as shown in  FIGS. 10 through 12 . A rigid end support plate  154  extends upwardly from the left end of the drum  14  and chassis of the machine, with an elongate tension roller support strut  156  cantilevered rigidly from the support plate  154  adjacent and substantially parallel to the rotational axis of the sanding drum  14 . The tension roller  16  is held in a cradle  158 , which extends from the strut  156  on a pivot shaft  160  and laterally across the chassis. The sanding drum  14  and generally parallel tension roller  16  (depending upon the limited pivotal motion of the tension roller in accordance with the belt centering system, described further below) define a belt tension plane coincident with the centerline CL between the drum  14  and centered roller  16 . 
     A spring  162  maintains pressure between the support strut  156  and the tension roller cradle  158 . Belt tension may be released by means of a rotary shaft  164 , which extends through the end support plate  154  and parallel to the support strut  156  to a shaft end support plate  166  extending from the inboard end of the support strut  156 . A release handle  168  is provided on the outer end of the tension release shaft  164 , with an actuating fork  170  extending from the shaft  164  and passing around each side of the spring  162  to bear on a transverse pin  172  above the tension roller cradle end of the spring  162 . When the tension release shaft  164  is rotated clockwise in the view of  FIG. 11  by means of its release handle  168 , the fork  170  bears down on the pin  172  to compress the spring  162 , thereby allowing the tension roller cradle  158  to slide toward the drum  14  along the pivot shaft  160  to release the tension on the sanding belt  20 . The lowered position of the tension roller cradle  158  is shown in broken lines in  FIG. 11 . 
     It will be noted in  FIG. 11  that the longitudinal axes of both the spring  162  and tension roller support strut  160  are angularly offset relative to the belt tension plane and centerline CL passing through the centers of rotation of the drum  14  and tension roller  16 , when the roller  16  is at its maximum extension from the drum  14 . The support strut  160  is also displaced forwardly of the belt tension plane and centerline CL, to define a caster offset and angle relative to the belt tension plane and centerline CL. Any laterally offset drag toward one end or the other of the tension roller  16  will result in the tension roller castering slightly about the pivot axis defined by the support strut  160 . 
     This angular offset is identical to the offset angle O between the horizontal axis and the plane P of pivotal rotation of the tension roller  16  and its cradle  158 , as shown in  FIG. 11 . This results in either end of the roller cradle  158  and its tension roller  16  pivoting forwardly and slightly upwardly, i.e. away from the drum  14  along the plane of pivotal rotation of the tension roller, when the tension roller  16  and its cradle  158  pivot away from precisely parallel alignment with the axis of the sanding drum  14 . This is caused when the sanding belt  20  shifts or “walks” toward one end of the roller  16 . 
     Each of the opposed ends  174   a ,  174   b  of the tension roller  16  has an end flange, respectively  176   a ,  176   b , extending therefrom. These flanges  176   a ,  176   b  serve to retain the sanding belt  20  on the tension roller  16 , and thus on the sanding drum  14 . The top plan view of the tension roller  16  shown in  FIG. 12  is used to provide an example of this operation, with the roller  16  being shown in solid lines in its neutral position and in broken lines with its right hand end  174   b  pivoted forwardly. (It will be understood that the pivotal displacement shown in broken lines in  FIG. 12  is exaggerated for clarity in the drawing Fig.) When the belt  20  shifts or “walks” to the end  174   b  of the tension roller  16 , the edge of the belt  20  contacts the corresponding tension roller flange  176   b . When this occurs, the contact of the belt edge with that flange  176   b  pushes that end  174   b  of the tension roller  16  about its caster pivot shaft  160 , causing that end of the tension roller to pivot forwardly. This results in a twisting of the sanding belt  20 , which causes the belt to shift laterally from its offset position at the forwardly pivoted end of the tension roller  16  and back toward the center. The forwardly pivoted end of the tension roller  16 , e.g. the second end  174   b  of the example shown in  FIG. 12 , also moves slightly upwardly due to the non-parallel axis of the pivot shaft  160  relative to the belt tension plane and centerline CL, i.e. away from the sanding drum  14 . This also causes the sanding belt  20  to shift or “walk” back toward the opposite lower end of the tension roller  16 . These two effects result in a continuing process during operation of the machine, with the belt  20  constantly and automatically correcting any minor misalignment errors. The roller  16  is also crowned slightly, i.e. having a slightly larger central diameter than at the ends, to provide further belt centering assistance. 
     It will be appreciated that the above described pivot or castering mechanism is but one of myriad mechanisms which may be used to cause the tension roller to caster or articulate as the sanding belt shifts laterally thereon, to cause the belt to shift back toward the center of the roller. For example, the roller could be cantilevered from the side plate of the chassis of the machine by a pair of parallel links, with their pivotal axes being angularly offset relative to the belt tension plane to cause the tension roller to shift slightly upwardly as it shifts forwardly due to sanding belt lateral movement on the roller. Another means of carrying out the belt centering function would be to provide a pair of non-parallel links to support the tension roller, with the projection of the links resulting in a virtual pivot point ahead of the tension roller about which the roller would seem to pivot. These mechanisms, as well as others, all result in the articulation of the roller as the belt shifts from a central position thereon, which further results in the roller shifting angularly relative to the sanding drum to cause the belt to walk back toward the center of the roller. 
     In conclusion, the present automated floor sanding machine provides numerous improvements over earlier devices of the related art. The mechanical and electronic means of raising and lowering the sanding drum by means of the drive wheels, greatly facilitates the operation of the machine. The speed control of the machine by the operator is also greatly facilitated by means of the articulated handle and its speed or torque control mechanism for the propulsion motor. The additional automated lifting and lowering of the drum by means of the drive wheels in accordance with the travel speed of the machine over the floor or other underlying surface, further facilitates use of the machine and assures that the operator cannot apply excessive sanding pressure to a single spot on the floor, thus assuring that the machine cannot sand or wear low spots in the floor. The forwardly and angularly offset pivotal axis of the tension roller further facilitates use of the device, as the sanding belt automatically remains centered on the tension roller, and thus on the sanding drum, at all times during operation. Yet, removal of the belt for replacement is easily accomplished by means of the pivotal release rod which releases tension on the tension roller. 
     The above noted features are particularly applicable to a “walk behind” type floor sander, as illustrated in the drawings for the present disclosure. However, it will be seen that the various inventive features may also be incorporated in other types of floor sanders, e.g. ride-on and ride behind type machines, as well. Also, it should be noted that while the present disclosure has described the machine as a floor sander, the various features described herein may be applied to virtually any machine operating on similar principles, e.g. drum type buffing and polishing machines, etc. It will also be seen that the various features of the present invention, with the exception of the automated belt centering mechanism, are adaptable to drum sanders wherein no tension roller is provided and the abrasive medium or sanding element extends circumferentially about the drum. Accordingly, the present automated machine will prove to be a most worthwhile piece of equipment to those engaged in the floor maintenance and other similar trades. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.