Abstract:
A surface maintenance vehicle with a compact cleaning head lift mechanism and suspension. The cleaning head lift mechanism and suspension adjust a scrub head to an operational mode and a transport mode, yet remain compact such that they are confined to specific areas of the surface maintenance vehicle.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to co-pending U.S. Provisional Patent Application Ser. No. 61/599,776 filed Feb. 16, 2012, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to surface cleaning machines having a cleaning head with a compact lift mechanism and suspension. 
       BACKGROUND OF THE INVENTION 
       [0003]    Floor cleaning in public, commercial, institutional and industrial buildings have led to the development of various specialized floor cleaning machines, such as hard and soft floor cleaning machines. These cleaning machines generally utilize a cleaning head that includes one or more cleaning tools configured to perform the desired cleaning operation on the floor surface. These cleaning machines include dedicated floor sweeping machines, dedicated floor scrubbing machines and combination floor sweeping and scrubbing machines. 
         [0004]    An example of a dedicated hard floor sweeping and scrubbing machine is described in U.S. Pat. No. 5,901,407, which is assigned to Tennant Company of Minneapolis, Minn. and which is hereby incorporated by reference in its entirety. The machine uses a cleaning head having two cleaning tools in the form of cylindrical brushes. The cleaning tools counter-rotate in the directions indicated by the arrows shown. Water and detergent are sprayed on the floor ahead of the brushes so the brushes can scour the floor at the same time they are sweeping debris from the floor. A vacuum squeegee removes liquid waste from the floor during the wet scrubbing and sweeping operations. The cleaning tools engage each other such that debris on the floor is swept between the two cleaning tools and is directed into a waste hopper by a deflector. 
         [0005]    An example of a dedicated floor sweeper is described in U.S. Pat. No. 4,571,771, which is assigned to Tennant Company of Minneapolis, Minn. and is hereby incorporated by reference in its entirety. The floor sweeper includes a cleaning head comprised of a rotating cylindrical brush that contacts the floor and throws loose debris into a hopper which is periodically emptied either manually or through a motorized lift. Combination floor sweeping and scrubbing machines were developed to avoid the necessity of having two machines. Some floor sweeping and scrubbing machines were created by mounting sweeping components to the front end of a dedicated scrubbing machine to making one large, multi-function machine. 
         [0006]    Scrubbing systems are well known in the art. Scrubbing systems commonly include a driver assembly and a cleaning head that is a rotatable scrubber in the form of a brush, pad, or the like. A control device may be utilized for controlling the degree of scrubbing (typically a function of down-force applied through the scrubber) applied to a floor surface depending upon the type and/or condition of floor surface intended to be scrubbed. The scrubber driver assemblies for scrubbing systems are well known in the art and commonly include one or more rotatable brushes driven by a driver motor affixed to a scrubber head. Scrubber heads of the prior art include a lift mechanism that selectively raises and lowers the scrub heads by an actuator coupled to the driver so as to achieve an intended down force or scrubbing pressure of the scrub pad against a floor surface. 
         [0007]    Some prior art scrub head lift mechanisms and suspensions have included a large number of parts, which can increase the cost and complexity of such mechanisms and suspensions. In addition, some prior art scrub head lift mechanisms and suspensions have a large footprint on the surface maintenance vehicle that can complicate packaging the scrub head lift mechanisms and suspensions within the confines of the vehicle. In addition, the packaging considerations of a relatively large scrub head lift mechanisms and suspensions make it difficult to use the same scrub head lift mechanisms and suspensions designs on different vehicles of different sizes. 
       SUMMARY 
       [0008]    Certain embodiments of the present invention include a floor surface maintenance machine that has a longitudinally extending frame, wheels connected to the frame, a scrub head, and a lift mechanism and suspension. In certain embodiments the scrub head is connected to the frame and includes a housing and a floor-engaging brush. The scrub head is adjustable to an operational mode and a transport mode. The lift mechanism and suspension includes a linear actuator operable to adjust the scrub head to the operational mode and the transport mode. The lift mechanism and suspension includes a main suspension arm pivotally coupled to the scrub head, a bell crank pivotally coupled to the main suspension arm, the linear actuator pivotally coupled to the bell crank, and a biasing linkage that restricts the pivoting between bell crank and main arm. The restricted pivoting permits the scrub head to rise and fall while passing over any undulations in the floor without requiring engagement of the linear actuator. 
         [0009]    Certain embodiments of the present invention include a floor surface maintenance machine that has a longitudinally extending frame, wheels connected to the frame, a scrub head, and a lift mechanism and suspension. The frame defines a lateral width and has a generally planar major top surface. In certain embodiments the scrub head is connected to the frame and includes a housing and a floor-engaging brush. The scrub head is adjustable to an operational mode and a transport mode. The lift mechanism and suspension includes a linear actuator operable to adjust the scrub head to the operational mode and the transport mode. In certain embodiments the entire lift mechanism and suspension is positioned within the lateral width of the frame. In certain embodiments, the entire lift mechanism and suspension is positioned lower than the generally planar major top surface of the frame. 
         [0010]    Certain embodiments of the present invention include a floor surface maintenance machine that has a longitudinally extending frame, wheels connected to the frame, a scrub head, and a lift mechanism and suspension. The frame defines a lateral width and has a generally planar major top surface. In certain embodiments the scrub head is connected to the frame and includes a housing and a floor-engaging brush. The scrub head is adjustable to an operational mode and a transport mode. The lift mechanism and suspension includes a linear actuator operable to adjust the scrub head to the operational mode and the transport mode. The linear actuator is adapted to raise the scrub head into the transport position for the transport mode and is adapted to lower the scrub head into an operating position with the floor for the operational mode. A coupling structure connects the scrub head to the frame. The coupling structure provides for movement of the scrub head between the transport position and the operating position. The linear actuator is connected to the coupling structure and to the scrub head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The following drawings are illustrative of particular embodiments of the invention and therefore do not limit the scope of the invention. The drawings are not necessarily to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
           [0012]      FIG. 1A  is an upper perspective view of an exemplary floor surface cleaning machine employing an embodiment of the compact scrub head lift mechanism and suspension of the present invention; 
           [0013]      FIG. 1B  is a lower perspective view of an exemplary floor surface cleaning machine employing an embodiment of the compact scrub head lift mechanism and suspension of the present invention; 
           [0014]      FIG. 2A  is a right side elevation view of a frame of the machine of  FIG. 1  and a portion of an embodiment of the scrub head and a portion of an embodiment of the compact scrub head lift mechanism and suspension of the present invention; 
           [0015]      FIG. 2B  is a top plan view of the frame and the portion of an embodiment of the scrub head and a portion of an embodiment of the compact scrub head lift mechanism and suspension of  FIG. 2A  with the frame shown in ghost; 
           [0016]      FIG. 3  is a right-side perspective view of a portion of an embodiment of the scrub head and compact scrub head lift mechanism and suspension of the present invention; 
           [0017]      FIG. 4  is an upper right-side perspective view of an embodiment of the compact scrub head lift mechanism and suspension of the present invention; 
           [0018]      FIG. 5  is an upper right-side perspective view of a portion of an embodiment of the compact scrub head lift mechanism and suspension of the present invention; 
           [0019]      FIG. 6  is a rear elevation view of a portion of an embodiment of the compact scrub head lift mechanism and suspension of the present application with some portions shown in ghost; 
           [0020]      FIG. 7  is a left-side elevation view of a portion of an embodiment of the compact scrub head lift mechanism and suspension of the present application; and 
           [0021]      FIG. 8  is a right-side perspective view of a portion of another embodiment of the scrub head and compact scrub head lift mechanism and suspension of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1A-B  are upper and lower perspective views, respectively, of an exemplary floor surface cleaning machine  100 . Embodiments of the machine  100  include components that are supported on a motorized mobile body. The mobile body comprises a frame supported on wheels  102  for travel over a surface, on which a cleaning operation is to be performed. The mobile body includes operator controls and a steering wheel  104 , which is positioned with respect to a seat  106  of machine  100 , so that a seated operator of machine  100  may steer a front center wheel  108  of machine  100 . Machine  100  is preferably powered by one or more batteries that may be contained in a compartment beneath the seat. Alternately, the power source may be an internal combustion engine, powered through an electrical cord, or one or more power cells, may be employed to power machine  100 . 
         [0023]    Cleaning components extend from an underside of the machine  100 . For example, a scrub head  110  is shown located at a middle portion of machine  100 . The scrub head  110  has a housing  112  that encloses two scrub brushes  114 . The brushes  114  are driven by two electric motors. An electric actuator attached between the scrub head  110  and the housing  112  raises the scrub head  110  for transport, lowers it for work, and controls its down pressure on the floor. Additional aspects of the electric actuator and associated mechanical coupling are described in more detail hereinafter. The scrub head  110  uses two disk scrub brushes  114  rotating about parallel vertical axes. Alternatively, scrub heads may be made with only one disk scrub brush, or one or more cylindrical brushes rotating about horizontal axes. While a scrub head  110  is depicted in the drawing figures, any appliance or tool for providing surface maintenance, surface conditioning, and/or surface cleaning to a surface may be coupled to an associated machine or vehicle in accordance with the present invention. 
         [0024]    Vehicle  100  includes a side brush assembly  116  for cleaning a larger floor envelope. Such side brush assemblies make it easier to clean near walls or other obstacles without damaging the machine or the wall while at the same time widening the cleaning path of the machine to increase productivity. The side brush assembly is mounted on the front, right side of machine  100  and swings outwardly away from the machine center and downwardly toward the surface to be cleaned. 
         [0025]    During wet scrubbing operations, water or a cleaning liquid contained in a tank  118  is sprayed to or poured on the surface beneath machine  100 , in proximity to the scrub head  110 . Brushes  114  scrub the surface and the soiled cleaning liquid is then collected by a fluid recovery system and deposited in a waste recovery tank  120 . One embodiment of the fluid recovery system of the machine  100  includes a vacuum squeegee mounted adjacent the rear end of the machine  100 . The vacuum squeegee generally comprises a squeegee  122  that extends across the width of the machine  100  and a frame that supports the squeegee  122 . The vacuum squeegee also includes a vacuum port  124  that is placed in vacuum communication with a vacuum fan. The vacuum fan operates to remove liquid and particle waste collected by the vacuum squeegee  122  for deposit in the waste recovery tank  120 . 
         [0026]    In alternate embodiments, the floor surface maintenance machines  100  may be combination sweeper and scrubber machines. In such embodiments, in addition to the elements describe above, the machines  100  may also include sweeping brushes and a hopper extending from the underside of the machine  100 , with the sweeping brushes designed to direct dirt and debris into the hopper. In still other embodiments, the machine  100  may be a sweeper only. In such embodiments, the machine  100  may include the elements as described above for a sweeper and scrubber machine, but would not include the scrubbing elements such as scrubbers, squeegees and fluid storage tanks (for detergent, recovered fluid and clean water). Alternatively, the machine  100  may be designed for use by an operator that walks behind the machine, or the machine may be configured to be towed behind a vehicle. 
         [0027]      FIG. 2A  is a right side elevation view of the frame  200  of the machine  100  and a portion of the scrub head  110  and its lift mechanism and suspension. Several components of the scrub head  110 , including the brushes  114  and their associated electric motors, have been omitted for clarity.  FIG. 3  is a right-side perspective view of a portion of the scrub head  110  and its suspension and lifting mechanism. Several more components of the scrub head have been omitted for clarity. The scrub head  110  includes a housing  112  that encloses and mounts both the scrub brushes and their associated electrical motors. In embodiments employing one or more disk scrub brushes rotating about vertical axes, the housing  112  is a deck. In embodiments employing one or more cylindrical brushes rotating about horizontal axes, the housing  112  is a wrap. Although the brushes  114  are omitted from  FIG. 2A , mounts  202  for each scrub brush are shown. 
         [0028]    Housing  112  is attached to the frame  200  by a lift mechanism and suspension  126  which allows it to be raised and lowered and allows the brushes  114  to conform to undulations in the floor. The housing  112  is attached to the frame  200  by a lift mechanism and suspension assembly  126  that includes control arms  204 , main arm  206 , bell crank  208 , linear actuator  210 , and associated coupling structures. Coupling structures fixedly attached or formed as part of the frame  200  are considered part of frame  200 , though. Control arms  204  may also be considered idler arms or drag links. One portion of the coupling structure includes lower brackets  212  of housing  112  for securing a lower end of each control arm  204  to housing  112  with pivoted connections and for securing a lower end of linear actuator  210  to housing  112  with pivoted connections. Another portion of the coupling structure includes rear bracket  214  of housing  112  that is for securing a lower end of main arm  206  to housing  112  with a pivoted connection. Lower brackets  212  and rear bracket  214  are bolted or otherwise fixedly secured to housing  112  via any known methods (bolted, welded, integrally formed, etc.), and thus may be considered part of frame  200 . Another portion of the coupling structure includes upper brackets  216  for securing an upper end of each control arm  204  to frame  200  with pivoted connections. Upper brackets  216  are welded to, integral to, or otherwise fixedly secured to frame  200 , and thus may be considered part of frame  200 . 
         [0029]    Frame  200  extends longitudinally and has a cross-section in the shape of an inverted-U. Although other frame elements are bolted, welded, or otherwise connected to frame  200 , frame  200  has a major top surface that is generally planar. As shown in  FIG. 2A , all the components of the lift mechanism and suspension  126  are positioned at a height lower than the dotted line designated at U, the generally horizontal plane that intersects the major top surface of the frame  200 . Accordingly, in certain embodiments, lift mechanism and suspension  126  (e.g., control arms  204 , main arm  206 , bell crank  208 , linear actuator  210 ) is compact in that it does not extend higher than or protrude through the major top surface of the vehicle frame  200 . Past suspension lift mechanisms have protruded up through the frame requiring that other components such as batteries be rearranged or required considerable space on either side of the lift mechanism. 
         [0030]    As shown in  FIG. 2B , vehicle  100  has a longitudinal centerline shown as a dotted line C 200 . In many embodiments of the present invention, the leadscrew of linear actuator  210  is located centrally of the vehicle. In the view shown in  FIG. 2B , longitudinal centerline C 200  runs through the leadscrew of linear actuator  210 . In alternate embodiments, the leadscrew is may extend slightly to the right or the left of the longitudinal centerline, such that it is on either side of the longitudinal centerline C 200  by less an amount less than 10% of the overall frame width. 
         [0031]    Also as shown in  FIG. 2B , the components of the lift mechanism and suspension  126  (e.g., control arms  204 , main arm  206 , bell crank  208 , linear actuator  210 ) remain within the lateral confines of the frame  200 . That is, the components of the lift mechanism and suspension  126  do not extend wider than frame  200 . Frame  200  is internal and may be considered as a spine frame, but it can be formed in many different manners besides with an inverted U-shape. 
         [0032]      FIGS. 5 and 6  illustrate additional aspects of the coupling of main arm  206  to bell crank  208 . In  FIG. 6 , the main arm is shown in ghost for added clarity. Main arm  206  includes a U-shaped bracket  300  that is welded, integral to, or otherwise fixedly secured to an interior slot of main arm  206 . Bell crank  208  has an inverted U-shape and is pivotally secured within U-shaped bracket  300  via pin  302 . That is, both bell crank  208  and U-shaped bracket  300  have apertures that are aligned to receive pin  302 . The pinned connection permits bell crank  208  to pivot relative to U-shaped bracket  300  and, therefore, relative to main arm  206 . 
         [0033]    The otherwise free pivoting of the bell crank  208  relative to the main arm  206  is restricted by a biasing linkage  304  that includes a bolt  306 , washer  308 , and an upper spring  310  and a lower spring  312 . The biasing linkage  304  provides limited pivoting between bell crank  208  and main arm  206  to permit the housing  112  (and therefore the entire scrub head  110 ) to rise and fall while passing over any undulations in the floor without requiring engagement of the linear actuator  210 . As shown best in  FIG. 6 , lower spring  312  is a coil spring the ends of which are sandwiched by the interior, central portions of both U-shaped bracket  300  and inverted U shaped bell crank  208 . Upper spring  310  is a coil spring, the ends of which are sandwiched between the outer, central portion of inverted U shaped bell crank  208  and washer  308 . Bolt  306  extends through both lower spring  312  and upper spring  310  to hold the springs in place and extends through U-shaped bracket  300  and inverted U shaped bell crank  208  through apertures in their central portions. The springs  310 ,  312  bias the bell crank to pivot to a neutral or default position relative to the main arm  206 . 
         [0034]      FIG. 5  illustrates additional aspects of the coupling of linear actuator to bell crank  208 . Linear actuator  210  is used to raise the housing  112  for transport, lower the housing for work in an operational mode, and control the down pressure of the housing  112  on the floor when in the operational mode. Linear actuator  210  preferably is an electric actuator having a leadscrew member. As in known in the art, leadscrew member has a thread set formed therein and has a distal end  314  which is movable in response to leadscrew rotation. Additional linear actuators may include hydraulic or hybrid electro-hydraulic devices (not shown). The distal end  314  of leadscrew member has a pin-receiving aperture  316  formed therein. A pin  318  is inserted through an aperture in one end of bell crank  208  and also inserted through (although shown without such insertion) the pin-receiving aperture  316  of distal end  314  secures distal end  314  to bell crank  208  with a pivoted connection. 
         [0035]    As noted above, linear actuator  210  is used to raise the housing  112  for transport, lower the housing for work in an operational mode, and control the down pressure of the housing  112  on the floor when in the operational mode. In  FIG. 2A , the linear actuator  210  has been actuated to raise the housing  112  upward off of the floor surface for transport. In such a mode, the scrub brushes  114  are also raised off of the floor. Referring to  FIG. 4 , distal end  314  is shown retracted toward the linear actuator  210  to a position T for transport mode.  FIG. 4  also illustrates the distal end  314  extended further away from linear actuator  210  to a position O for the operational mode. It should be noted that while distal end  314  is shown disconnected from linear actuator  210  in position O, this does not happen in reality and is only shown in this manner to illustrate the location of position O relative to position T. As shown in  FIGS. 3-6 , main arm  206  includes a resilient pad  320  that functions to stop further rotation of main arm  206  about pivot  322 . Main arm  206  can rotate until pad  320  abuts the upper wall of frame  200 . This may occur when the scrub head is moved to the transport position. Many prior art scrub heads employ an actuator that mounts to the frame of the vehicle. As may be understood from the embodiments discussed above, the actuator  210  mounts between the housing  112  and the bell crank  208  and does not mount to the frame  200 . Accordingly, the pivotal connections on both ends of the actuator  210  move up or down as the actuator  210  moves the scrub head between the operational and transport positions. Moreover, as noted above, leadscrew of the actuator  210  is generally centered on the vehicle. 
         [0036]    In operation, when in the transport mode, the weight of the scrub head  110  creates a downward force on main link  206 , causing it and its U-shaped bracket  300  to rotate relative to the bell crank  208 , thereby compressing upper spring  310 . As the scrub head is moved into the operational mode, the actuator  210  extends and lowers the housing  112  such that the scrub brushes  114  are lowered onto the underlying floor surface. When the underlying surface supports the weight of the scrub head  110 , the main link  206  and its U-shaped bracket  300  rotate relative to bell crank  208  into a neutral position generally centered between upper spring  310  and the lower spring  312  (assuming the springs are equal). As the actuator  210  extends further when moving into the operational mode, scrub head  110  does not compress much further into the underlying floor surface, thus causing bell crank  208  to rotates relative to main link  206  such that lower spring  312  is compressed. The compression of lower spring  312  increases the downforce of the scrub head  110  onto the underlying floor surface beyond just the weight of the scrub head  110 . 
         [0037]    In scrubbing, if the scrub head  110  encounters undulations in the floor, the biasing linkage  304  permits limited pivoting of the bell crank  208  relative to the main link  206  to permit the scrub head  110  to rise when encountering a high spot and drop and encountering a low spot without having to immediately engage the linear actuator  210 . For instance, as scrub head  110  encounters a high spot, the rising housing  112  causes bell crank  208  to pivot in a manner that further compresses lower spring  312 . As scrub head encounters a low spot, the weight of scrub head  110  and the already compressed lower spring  312  push scrub head  110  downward to remain flush with the dip in the underlying floor surface. If the dip is low enough, main link  206  and bell crank  208  could rotate relative to each other enough that upper spring  310  could be compressed instead of lower spring  312 . 
         [0038]    Referring back again to  FIG. 2A , main arm  206  connects to rear bracket  214  at pivot point  322 . A transverse centerline C 100 , dividing the front and rear of housing  112  in half is shown in phantom. It may be seen that pivot  322  is located to the rear of transverse centerline C 100  of housing  112 . In the embodiment shown, pivot  322  is located at about 75 percent of the distance from the front to the rear of housing  112 , or halfway between the transverse centerline C 100  and the rear of the housing  112 . In certain embodiments the pivot  322  is located between 65 and 85 percent of the distance from the front to the rear of housing  112 . The down force imparted on housing  112  by main arm  206  at pivot  322  is therefore directed towards the rear half of housing  112 . Even though control arms  204  are pivotally connected between frame  200  and housing  112 , the control arms  204  are rigid. Thus, the rigidity of control arms  204  helps prevent the downward force from main arm  206  from tilting housing about pivot  322  to an orientation not parallel to the underlying floor. That is, the combination of control arms  204  and the relatively rearward location of pivot  322  maintains the orientation of housing  112  parallel to the floor throughout the travel of the scrub head  110  between its transport position and operational position and when traversing undulations in the floor. By keeping the scrub head  110  parallel to the floor, the rigidity of control arms  204  also helps distribute the non-centrally located downward force from main arm  206  more evenly such that scrub brushes  114  provide a fairly uniform down force or pressure against the underlying floor. 
         [0039]      FIG. 7  is a left-side elevation view of a portion of an embodiment of the compact scrub head lift mechanism and suspension with some portions shown in ghost. The features (and reference numerals) already described for other drawing figures, also apply to the embodiment of  FIG. 7 . Similar to the embodiment described above, a pin  318  is inserted through an aperture in one end of bell crank  208  and through the distal end of the leadscrew member to form a pivotal connection. Also, bell crank  208  has an inverted U-shape and is pivotally secured within U-shaped bracket (not shown) via pin  302 . The pinned connection at  302  permits bell crank  208  to pivot relative to U-shaped bracket and, therefore, relative to main arm (not shown in  FIG. 7 ). 
         [0040]      FIG. 7  shows a modified embodiment of a biasing linkage  304 . The biasing linkage  304  restricts the otherwise free pivoting of the bell crank  208  relative to the main arm. Similar to  FIGS. 5 and 6 , the biasing linkage in  FIG. 7  includes a bolt  306 , washer  308 , and an upper spring  310  and a lower spring  312 . Lower spring  312  is a coil spring the ends of which are sandwiched by the interior, central portions of both U-shaped bracket  300  and inverted U shaped bell crank  208 . Upper spring  310  is a coil spring, the ends of which are sandwiched between the outer, central portion of inverted U shaped bell crank  208  and washer  308 . Bolt  306  extends through both lower spring  312  and upper spring  310  to hold the springs in place and extends through U-shaped bracket  300  and inverted U shaped bell crank  208  through apertures in their central portions. The springs  310 ,  312  bias the bell crank to pivot to a neutral or default position relative to the main arm  206 . 
         [0041]    In the embodiment in  FIG. 7 , the biasing linkage  304  also includes a sleeve  324  that surrounds bolt  306  and upper spring  310  and is also sandwiched between and retained by the outer, central portion of inverted U shaped bell crank  208  and washer  308 . Sleeve  324  could be of even smaller diameter such that it is positioned radially between the bolt  306  and the inner, radial surface of upper spring  310 . Although sleeve  324  is only shown proximate the upper spring  310 , a sleeve  324  could also be employed proximate the lower spring  312 . Sleeve  324  functions as an upstop that stops further compression of upper spring  310  when the scrub head is moved to the transport position. That is, when in the transport mode or when moving from the operational mode to the transport mode, the weight of the scrub head  110  creates a downward force on main link, causing it and its U-shaped bracket to rotate relative to the bell crank  208 , thereby compressing upper spring  310 . In some designs it is desirable to use a relatively elongated upper spring  310  or an upper spring with a relatively low spring constant. In such designs, it may also be desirable to limit the compression of upper spring  310  via the use of sleeve  324  acting as a stop. Sleeve  324  may be made of any material. However, if sleeve  324  is formed of a resilient material, such as plastic or rubber, sleeve  324  also acts as a bumper to help absorb the force of bell crank  208  forcefully compressing upper spring  310 . 
         [0042]    Referring to  FIG. 8 ,  FIG. 8  is a right-side perspective view of a portion of the scrub head  110  and its suspension and lifting mechanism of an alternative embodiment of the invention, similar to that shown in  FIG. 3 . As in  FIG. 3 , several components of the scrub head have been omitted for clarity. The features (and reference numerals) already described for the embodiment in  FIG. 3  also apply to the embodiment of  FIG. 8 . Like numerals denote like elements. In certain embodiments, such as the one shown in  FIG. 8 , the housing  112  (which is shown as a deck in  FIG. 8 ) is formed of steel. Similar to  FIG. 3 , lower brackets  212  and rear bracket  214  are bolted or otherwise fixedly secured to housing  112  via any known methods (bolted, welded, integrally formed, etc.), and thus may be considered part of frame  200 . However, as shown in  FIG. 8 , lower brackets  212  and rear bracket  214  are joined together for added strength. 
         [0043]    Additional considerations and alternative embodiments with respect to the present invention may include substituting or eliminating certain components and/or subcomponents of the illustrated embodiment. For example, coil springs can be replaced with compliant rubber links or torsion springs, or some other compliant metal link. In addition, alternative pivot join designs may be used, such as spherical bearings, and different bearing styles. Components eliminated (or added) to reduce (or add) adjustability of the position of the scrub head on the machine. To the extent one substitutes a wrap for the scrub deck, cams may be included in the pivot joint between the wrap and the drag links. 
         [0044]    Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details, representative apparatus and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant&#39;s general inventive concept.