Abstract:
A control system for estimating the approximate relative position of an electric linear actuator on a surface maintenance machine. The control system includes device for selectively coupling the electric motor of the linear actuator to the electric power source, device for measuring or estimating the current and voltage of the electric motor, device for estimating the motor speed based on the measured values of current and voltage, and storage device for storing values of estimated motor speed and integrating device for determining approximate linear actuator position, wherein the integrating device integrates the motor speed over time to determine the approximate position of the linear actuator position.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to an apparatus and method of use for determining the approximate relative position of an actuator or tool controlled by the actuator and relates generally to surface maintenance or conditioning machines, and more particularly to those machines employing one or more surface maintenance or conditioning appliances or tools that perform one or more tasks including, among others, scrubbing, sweeping, and polishing or burnishing. 
     BACKGROUND OF THE INVENTION 
     Surface maintenance vehicles that perform a single surface maintenance or surface conditioning task are, of course, well known. Surface maintenance vehicles are generally directed to perform work in diverse maintenance, conditioning and cleaning applications such as for flooring surfaces. In this disclosure, the term floor refers to any support surface, such as, among others, floors, pavements, road surfaces, ship decks, and other surfaces to be cleaned and the like. 
     Commonly floor or surface maintenance machines are constructed having a single surface conditioning appliance or system so as to only sweep, others to scrub, while still others only to polish or burnish. It is of course possible to construct a single surface maintenance machine to perform one or more of the aforementioned surface maintenance tasks. One example of a multi-task floor conditioning machine is disclosed in U.S. Pat. No. 3,204,280, entitled “Floor Cleaning &amp; Waxing Machine,” the entire disclosure of which is incorporated by reference herein in its entirety for any and all purposes. Another is disclosed in U.S. Pat. No. 5,483,718, entitled, “Floor Scrubbing Machine Having Impact Energy Absorbtion,” the entire disclosure of which is incorporated be reference herein in its entirety for any and all purposes. Disclosed therein is a forward mounted scrubber assembly that is followed by a squeegee assembly. 
     Scrubbing systems are well known in the art. Scrubbing systems commonly include a driver assembly and 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 have been selectively raised and lowered 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. Examples of the latter are taught in U.S. Pat. Nos. 4,757,566, 4,769,271, 5,481,776, 5,615,437, 5,943,724, and 6,163,915, the entire disclosures of which are incorporated by reference herein in its entirety for any and all purposes. 
     Limit switches have been used to determine the relative position of the actuator tool. Limit switches are mechanical switches and, depending particularly on the operating environment, may be prone to damage or failure. Some limit switches are integrated within the housing of linear actuator to minimize damage or obstruction of the switch contacts. In some applications, a pair of limit switches can be used to determine the end of range positions of the actuator. In such applications, the pair of limit switches are unable to provide information as to actuator tool position within the range of limits. 
     Accordingly, it would be desirable to provide an apparatus and method for determining the position of an actuator or tool controlled by an actuator. Additionally, it would be desirable to eliminate the use of one or more limit switches to determine actuator or tool position. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an efficient structure and method for determining the approximate relative position of an actuator tool, such as a working head in engagement with a surface to be cleaned. The invention further relates to a method of using a control structure to determine the actuator tool position while performing tasks of surface cleaning, surface maintenance, surface conditioning and the like. While the present invention is described and depicted primarily with reference to a cleaning head, the present invention finds diverse application in the art of surface cleaning, maintenance, conditioning and the like. Accordingly, the present invention is readily adaptable to a machine having one or more of the following applications, including without limitation, such cleaning heads designated and adapted to: burnish, polish, scrub, sweep, brush, treat and wipe a surface to be cleaned wherein an ability to determine the position of the working tool is beneficial. Of course, such cleaning head implements or cleaning head appliances may each be provided with an embodiment of the present invention and coupled to a single dedicated surface maintenance vehicle or to more than one such cleaning head coupled to a single vehicle. 
     In one embodiment, the invention is particularly applicable to a floor scrubbing machine having a scrub head mounted in front of the machine chassis. The scrub head includes a scrub brush or pad and a scrub driver. A linear actuator is utilized to raise and lower the scrub head relative to the floor surface. 
     Estimating the position of the actuator is a key element in the control strategy of the present invention The reliability of a motion control system can be greatly enhanced by increasing the accuracy of the linear actuator position estimation according to the present invention. Adding external components (sensors, limit switches, etc.) has a negative impact on machine reliability. By monitoring actuator voltage and current, the impedance of the actuator motor can be mathematically determined (R=V/I). As the load on the motor changes, the relationship between the applied motor voltage and speed diminishes. The impedance of the motor is a more accurate indicator of speed, regardless of motor load. 
     The linear actuator control system of the present invention performs the steps of measuring motor voltage, measuring motor current, using a mathematical formula, or table, or both to estimate motor speed, and integrating the speed over time to determine the approximate position of an actuator or tool controlled by an actuator. While the actuator motor is in operation, the voltage applied to the motor, and the current drawn by the motor are measured. From the measured voltage and current information, the impedance of the motor can be calculated (R=V/I). The impedance of the motor is approximately proportional to the motor speed. By continuously assessing motor speed, the actuator position may be determined via integration of motor speed and time data. 
     The present invention provides several advantages over both prior art and contemporary apparatus for determining relative tool position. The present invention may be implemented without physical limit switches. As a result the present invention is generally lower cost, easier to maintain and less prone to breakage than prior art (and complex contemporary) cleaning head position determining mechanisms and algorithms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a surface maintenance vehicle having a cleaning head coupled to said vehicle and incorporating aspects according to the present invention. 
         FIG. 2  is a perspective view of portions of the surface maintenance vehicle of  FIG. 1  shown in an unassembled, exploded view adjacent the frame of a surface maintenance vehicle and wherein coupling between such parts is shown in ghost. 
         FIG. 3  is a flow chart of steps of the method of estimating linear actuator position according to the present invention. 
         FIG. 4  is a flow chart of steps of another method of estimating linear actuator position according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A floor scrubbing machine which uses the present invention is shown in normal operating position in  FIG. 1 . The scrubbing machine  10  has two front wheels  12  and two rear caster wheels  14 , and a transaxle  16  providing traction drive to the front wheels. The transaxle and rear casters are attached to a frame  18 , which supports a housing  20 . This housing encloses rechargeable batteries  22  which supply energy to power the machine. It also contains a recovery tank to hold soiled scrub water recovered by a vacuum squeegee  24  from a floor  26  being scrubbed. A hinged lid  28  contains a tank for clean scrubbing solution to be dispensed to the floor and a vacuum fan to lift soiled scrub water from the floor via the squeegee  24  and deposit it in the recovery tank. A control console  30  provides necessary controls for an operator who walks behind the scrubber. 
     A scrub head  32  is shown in  FIG. 1  in position to scrub the floor  26 . A housing  34  encloses two scrub brushes  36 . The brushes  36  are driven by two electric motors  38  which are shown in  FIG. 2  (but omitted for clarity in  FIG. 1 ). An electric linear actuator  40  attached between the scrub head  32  and the housing  20  raises the scrub head  32  for transport, lowers it for work, and controls its down pressure on the floor. Linear actuator  40  includes an electric motor  41 . Additional aspects of the electric actuator  40  and associated mechanical coupling are described in more detail hereinafter. 
     The scrub head  32  as illustrated in  FIGS. 1–2  uses two disk scrub brushes  36  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. All of these variations can be applied to this invention. The illustrated scrubber is a relatively small model, controlled by an operator walking behind it. Scrubbers are made in much larger sizes, some of which have the operator riding on them. Again, the invention can be applied to larger machines if the essential elements of the invention are observed. While a scrub head  32  is depicted in  FIGS. 1–2 , any appliance or tool for providing surface maintenance, surface conditioning, and/or surface cleaning to a surface may be controlled in an associated machine or vehicle in accordance with the present invention. 
     The scrub head  32  is attached to the frame  18  by a coupling structure which allows it to be raised and lowered and allows the brushes  36  to conform to undulations in the floor  26 . The scrub head  32  is attached to the frame  18  by lower control arms  42 , a guide linkage  48 ,  50  and electric linear actuator  40  and associated coupling structure, including an upper mount assembly  52  for securing one end of the linear actuator to the housing  20 , and a lower bracket  60  for securing the other end of the linear actuator  40  to the scrub head  32 . Additional aspects of the lower bracket  60  are provided hereinafter. The two lower control arms  42  are attached to the frame  18  and the scrub head housing  34  with pivoted connections at their ends. Two upright arms  70  are also connected to scrub head  32 . Guide  50  is attached to the front wall of the housing  20 . Guide  50  provides a slot  76  within which roller  48  can move up and down. This slot  76  has an arcuate lower portion which is generally vertical and an upper portion which slopes up and toward the rear. During normal operation roller  48  rides more or less midway in the lower portion of slot  76 , where it moves through the same arc as the front pivots of arms  42  to keep the brushes  36  and scrub head  32  parallel to the floor  26  as the scrub head  32  rises and falls while passing over any undulations in the floor. Two springs  78  are attached between the scrub head housing  34  and the arms  70 . Since the arms  70  are constrained at their upper ends by slot  76  and at their lower ends by pivot  74 , the action of springs  78  is to tend to tilt the forward part of the scrub head upward around pivot  74 . Scrub head  20  is caused to tilt when it is raised to ease access to the components thereof by an operator of vehicle  10 . Additional aspects of the scrub head are disclosed in U.S. Pat. No. 5,483,718, incorporated by reference herein. 
     Linear actuator  40  is used to raise the scrub head  32  for transport, lower it for work in a first operational mode, and controls its down pressure on the floor in a second operational mode, such as disclosed in U.S. Pat. No. 6,618,888, incorporated by reference herein. Linear actuator  40  preferably is an electric actuator having a leadscrew member  80 . As in known in the art, leadscrew member  80  has a thread set formed thereupon and has a distal end  82  which is movable in response to leadscrew  80  rotation. The distal end  82  of leadscrew member  80  has a pin-receiving aperture  84  formed therein. A pin received within aperture  84  engages bracket  60  to operatively couple the scrub head  32  to housing  20 /frame  18 . Electric motor  41  of linear actuator  40  is controlled via controller  100 . Electric motor  41  is operatively coupled to the batteries  22  via a controlled switch  102 . Voltage data and current data of electric motor  41  may be presented to controller  100  by voltage sensor  104  and current sensor  106  which are shown in phantom lines in  FIG. 1  as one of ordinary skill in the art would appreciate a variety of sensors which could be used to determine motor  41  voltage and current draw. 
     Estimating the position of the actuator  40  is a key element in the control strategy of machine  10 . The reliability of a motion control system can be greatly enhanced by increasing the accuracy of the linear actuator  40  position estimation. Adding external components (sensors, limit switches, etc.) has a negative impact on machine  10  reliability. By monitoring actuator voltage and current, the impedance of the actuator motor can be mathematically determined (R V/I). As the load on the motor changes, the relationship between the applied motor voltage and speed diminishes. The impedance of the motor is a more accurate indicator of speed, regardless of motor load. 
     The linear actuator control system of the present invention performs the steps of measuring motor voltage, measuring motor current, using a mathematical formula, or table, or both to estimate motor speed, and integrating the speed over time to determine the approximate position of an actuator or tool controlled by an actuator. While the actuator motor is in operation, the voltage applied to the motor, and the current drawn by the motor are measured. From the measured voltage and current information, the impedance of the motor can be calculated (R=V/I). The impedance of the motor is approximately proportional to the motor speed. By continuously assessing motor speed, the actuator position may be determined via integration of motor speed and time data. 
     The linear actuator control system may include software, hardware, or combinations of both. The control system may be implement using a variety of digital and/or analog control devices. Controller  100  performs some of the functions necessary to determine estimated actuator  40  position. In one embodiment, a programmable digital controller may be programmed to implement the methods of the present invention to determine the approximate position of the actuator  40  or tool controlled by actuator  40 . Those of ordinary skill in the art would appreciate that there are many ways to measure the voltage and current in a back-emf circuit. 
       FIG. 3  represents steps of one embodiment of a linear actuator control system according to the present invention. The linear actuator  40  is connected to the source of electrical energy (battery  22 ) in step  112 . Controller  100  receives data representative of actuator current and voltage in step  114 . Controller  100  utilizes the current and voltage data from step  114  to estimate the speed of actuator  40 , as indicated in step  116 . In step  118 , the position of actuator  40  is determined by integrating speed data from step  116  over time. Controller  100  may use or pass position and/or speed data to subsequent devices. Controller  100  may also use the position data from step  118  to control activation of actuator  40 , as indicated in  120 . Those of ordinary skill in the arts would appreciate the various approaches to implementing such a control system utilizing hardware, software or a combination of both. For example, in another embodiment of the present invention the voltage applied across the electric motor of the linear actuator may be estimated (instead of directly sensed) with knowledge of the motor duty cycle.  FIG. 4  represents steps of another embodiment of a linear actuator control system according to the present invention. In step  116 , an approximation of motor voltage can be made by multiplying battery voltage and percent duty cycle by a correction factor, k. For example, motor voltage may be estimated by using the following formula: MV≈battery voltage×% duty cycle×k 
     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.