Patent Publication Number: US-11638669-B2

Title: Lift control systems for lifting devices and lifting devices comprising the same

Description:
CROSS REFERENCE To RELATED APPLICATIONS 
     The present specification is a continuation of U.S. patent application Ser. No. 16/995,060 entitled “LIFT CONTROL SYSTEMS FOR LIFTING DEVICES AND LIFTING DEVICES COMPRISING THE SAME” filed Aug. 17, 2020 which is a continuation of U.S. patent application Ser. No. 16/395,918 entitled “LIFT CONTROL SYSTEMS FOR LIFTING DEVICES AND LIFTING DEVICES COMPRISING THE SAME” filed Apr. 26, 2019 (now U.S. Pat. No. 10,780,004) which is a continuation of U.S. patent application Ser. No. 15/360,373 entitled “LIFT CONTROL SYSTEMS FOR LIFTING DEVICES AND LIFTING DEVICES COMPRISING THE SAME” filed Nov. 23, 2016 (now U.S. Pat. No. 10,322,046) which is a continuation of U.S. patent application Ser. No. 13/796,100 entitled “LIFT CONTROL SYSTEMS FOR LIFTING DEVICES AND LIFTING DEVICES COMPRISING THE SAME” filed Mar. 12, 2013 (now U.S. Pat. No. 9,527,699) which is a continuation of U.S. patent application Ser. No. 12/717,532 entitled “LIFT CONTROL SYSTEMS FOR LIFTING DEVICES AND LIFTING DEVICES COMPRISING THE SAME” filed Mar. 4, 2010 (now U.S. Pat. No. 8,474,794) which claims priority to U.S. provisional application Ser. No. 61/158,050 filed Mar. 6, 2009 and entitled “CONTROL AND DIAGNOSTIC SYSTEMS FOR LIFTING DEVICES,” each of which is herein incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present specification generally relates to lifting devices and, more specifically, to lift control systems for use in conjunction with lifting devices. 
     BACKGROUND 
     Lifting devices, such as patient lifts used in the health care industry, may generally comprise an actuator, such as an electric motor or similar actuator, which may be coupled to a mechanical lifting arm or cable lifting system. The actuator facilitates actuation of the mechanical lifting arm or cable lifting system thereby raising and/or lowering a load attached to the lifting arm or cable lifting system. For example, when the lifting device is a patient lift, a sling or other support apparatus may be attached to the mechanical lifting arm or cable lifting system. A patient may be positioned in the sling and a lift control system coupled to the actuator may be used by an operator to activate the actuator which, in turn, raises and/or lowers the patient by actuating the mechanical lifting arm or cable lifting system. The electrical current supplied to the actuator by the lift control system may vary depending on the weight of the patient being lifted. For example, lifting a heavier patient may require a relatively greater amount of electrical current be supplied to the actuator to facilitate lifting as compared to a relatively lighter patient. 
     Repeated and prolonged use of the lifting device may result in wear and/or degradation of the performance of the lifting device thus necessitating periodic maintenance. Such maintenance may include verification of the operation of the lifting device and repair or replacement of various components of the lifting device. However, the frequency and type of maintenance required may vary depending on a variety of factors including, but not limited to, the amount and frequency of use of the lifting device and the weight of the loads lifted and/or lowered with the lifting device. Such variations may not be adequately addressed through periodic maintenance. 
     Accordingly, a need exists for alternative lift control systems for use in conjunction with servicing and maintaining lifting devices. 
     SUMMARY 
     According to one embodiment, a lift control system for operating a lifting device comprising a lift actuator coupled to a lift arm includes a control unit comprising a processor with a memory communicatively coupled to the processor and having computer readable and executable instructions. A battery is electrically coupled to the control unit in addition to at least one indicator. The processor executes the computer readable and executable instructions to: determine an accumulated number of initiated battery charging events; determine an accumulated number of incomplete battery charging events; determine an accumulated number of battery replacements; determine at least one operating characteristic of the lifting device and an operating time of the lifting device as the lifting device is actuated; determine an accumulated load-time parameter for the lifting device based on the at least one operating characteristic and the operating time; store the accumulated load-time parameter in the memory of the lift control system; compare the accumulated load-time parameter to a service constant; and provide an indication with the at least one indicator that a lift structural component requires service based on the comparison of the accumulated load-time parameter to the service constant. 
     In another embodiment, a lifting device for raising and lowering a payload coupled to the lifting device includes a lift mast mechanically coupled to a base at a first end of the lift mast and a lift arm pivotally coupled to the lift mast at a second end of the lift mast. A lift actuator is mechanically coupled to the lift mast and the lift arm such that actuation of the actuator raises or lowers the lift arm relative to the base. A lift control system is communicatively coupled to the lift actuator and includes a control unit comprising a processor and a memory having computer readable and executable instructions. At least one indicator may be electrically coupled to the control unit. The processor executes the computer readable and executable instructions to: determine at least one operating characteristic of the lifting device and an operating time of the lifting device as the lifting device is actuated; determine an accumulated load-time parameter for the lifting device based on the at least one operating characteristic and the operating time; store the accumulated load-time parameter in the memory of the lift control system; compare the accumulated load-time parameter to a service constant; and provide an indication with the at least one indicator that a lift structural component requires service based on the comparison of the accumulated load-time parameter to the service constant. 
     In another embodiment, a method for operating a lifting device comprising a lift actuator for raising and lowering a load coupled to the lifting device includes: determining an operating characteristic of the actuator as the actuator is actuated; determining an operating time of the actuator as the actuator is actuated; determining an accumulated load-time parameter for the actuator based on the operating characteristic and the operating time; comparing the accumulated load-time parameter to a service constant indicative of a structural component of the lifting device requiring service; activating an indicator when the accumulated load-time parameter is greater than the service constant; and servicing a structural component of the lifting device when the indicator is activated. 
     These and additional features provided by the embodiments of the present invention will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the inventions defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIGS.  1 A and  1 B  depict a lifting device according to one or more embodiments shown and described herein; 
         FIG.  2    schematically depicts a block diagram of a lift control system for use in conjunction with a lifting device according to one or more embodiments shown and described herein; 
         FIG.  3    depicts a wireless controller for use in conjunction with a lift control system according to one or more embodiments shown and described herein; and 
         FIG.  4    depicts a wireless diagnostic monitor/controller for use in conjunction with a lift control system according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  2    generally depicts a schematic embodiment of a lift control system  200  for use in conjunction with a lifting device. The lift control system  200  may generally comprise a control unit  202  electrically coupled to the lift actuator  204  and base actuator  206  of the lifting device. The control unit  202  may be operable to actuate the base and lifting arm of the lifting device by sending control signals to the base actuator  206  and the lift actuator  204 , respectively. The control unit  202  may also be operable to determine at least one operating characteristic of the lifting device and an operating time of the lifting device and, based on these values, provide an indication of when a structural component of the lifting device requires service. The lifting device and the lift control system  200  and methods of using the same will be described in more detail herein. 
     Still referring to  FIG.  2   , it will be understood that the solid and dashed arrows generally indicate the interconnectivity of various components of the lift control system  200  and lifting device shown and described herein. It should also be understood that the arrows may also be indicative of electrical signals propagated between various components of the lift control system  200  and the lifting device. For example, the arrows may be indicative of a control signal supplied by the control unit  202  to the lift actuator  204  and/or base actuator  206 , or a data signal and/or control signal propagated between the wireless hand control  210  and the control unit  202  and/or the diagnostic monitor/control  208  and the control unit  202 . Further, it will be understood that the solid arrows are indicative of a wired connection between various components while the dashed lines are indicative of a wireless connection between various components. 
     Referring now to  FIGS.  1 A and  1 B , a lifting device  100  according to one or more embodiments of the present invention is schematically illustrated. The lifting device  100  may generally comprise a base  102 , a lift mast  104  and a lift arm  106 . The base may comprise a pair of base legs  108 A, 108 B which are pivotally attached to a cross support  132  at base leg pivots  144 A,  144 B such that the base legs  108 A,  108 B may be pivotally adjusted with respect to the lift mast  104  as indicated by the arrows. The base legs  108 A,  108 B may be pivoted with the base actuator  206  which is mechanically coupled to both base legs  108 A,  108 B with base motor linkages  125 ,  126 . In one embodiment, the base actuator  206  may comprise a linear actuator such as a motor mechanically coupled to telescoping threaded rods connected to the bases motor linkages  125 ,  126  such that, when an armature of the motor is rotated, one of the threaded rods is extended or retracted relative to the other. For example, in the configuration shown in  FIG.  1   , when the rods are extended, the base legs  108 A and  108 B are pivoted towards one another and, when the rods are retracted, the base legs  108 A and  108 B are pivoted away from one another. The base legs  108 A,  108 B may additionally comprise a pair of front castors  130 A,  130 B and a pair of rear castors  128 A,  128 B. The rear castors  128 A,  128 B may comprise castor brakes (not shown). 
     In one embodiment, the base  102  may further comprise a mast support  122  disposed on the cross support  132 . In one embodiment, the mast support  122  may be a rectangular receptacle configured to receive the lift mast  104  of the lifting device. For example, a first end of the lift mast  104  may be adjustably received in the mast support  122  and secured with a pin, threaded fastener, or a similar fastener coupled to the adjustment handle  124 . The pin or threaded fastener extends through the mast support  122  and into a corresponding adjustment hole(s) (not shown) on the lift mast  104 . Accordingly, it will be understood that the position of the lift mast  104  may be adjusted vertically (e.g., in the +/−Z direction on the coordinate axes shown in  FIG.  1 A ) with respect to the base  102  by repositioning the lift mast  104  in the mast support  122 . The lift mast  104  may further comprise at least one handle  118  coupled to the lift mast  104 . The handle  118  may provide an operator with a grip for moving the lifting device  100  on the casters. Accordingly, it will be understood that, in at least one embodiment, the lifting device  100  is mobile. 
     The lifting device  100  may further comprise a lift arm  106  which is pivotally coupled to the lift mast  104  at the lift arm pivot  138  at a second end of the lift mast such that the lift arm  106  may be pivoted (e.g., raised and lowered) with respect to the base  102 .  FIG.  1 A  shows the lift arm  106  in the fully raised position while  FIG.  1 B  shows the lift arm in the fully lowered position. The lift arm  106  may comprise at least one attachment accessory  136  coupled to the lift arm  106  with an attachment coupling  148 . In the embodiment shown in  FIGS.  1 A and  1 B  the attachment coupling  148  is pivotally attached to the lift arm  106  at an end of the lift arm  106  opposite the lift arm pivot  138 . In one embodiment, the attachment coupling  148  is pivotally attached to the lift arm  106  at attachment pivot  142  such that the attachment accessory  136  (a sling bar in the illustrated embodiment) may be pivoted with respect to the lift arm  106 . However, it should be understood that, in other embodiments, the attachment coupling  148  may be fixedly attached to the lift arm  106  or that the attachment accessory  136  may be directly coupled to the lift arm  106  without the use of an attachment coupling  148 . 
     In the embodiments described herein, the lifting device  100  is a mechanized lifting device. Accordingly, raising and lowering the lift arm  106  with respect to the base  102  may be achieved using an actuator such as a lift actuator  204 . In the embodiments shown, the lift actuator  204  is a linear actuator which comprises a motor  110  mechanically coupled to an actuator arm  114 . More specifically, the motor  110  may comprise a rotating armature (not shown) and the actuator arm  114  may comprise one or more threaded rods coupled to the armature such that, when the armature is rotated, the threaded rods are extended or retracted relative to one another and the actuator arm  114  is extended or retracted. In the embodiment shown in  FIG.  1   , the lift actuator  204  further comprises a support tube  116  disposed over the actuator arm  114 . The support tube  116  provides lateral support (e.g., support in the X and/or Y directions) to the actuator arm  114  as the actuator arm  114  is extended. 
     The lift actuator  204  may further comprise one or more limit switches coupled to the actuator arm  114 . For example, the actuator arm  114  may comprise an upper limit switch (not shown) and a lower limit switch (not shown) which are mechanically coupled to the actuator arm  114  and electrically coupled to a control unit  202 . The upper limit switch may provide the control unit  202  of the lifting device  100  with an electrical signal indicating that the actuator arm is fully extended (i.e., at an upper end position) while the lower limit switch may provide the control unit  202  with an electrical signal indicating that the actuator arm  114  is fully retracted (i.e., at a lower end position), as will be described in more detail herein. 
     In the embodiment shown in  FIGS.  1 A and  1 B , the lift actuator  204  is fixedly mounted on the lift mast  104  and pivotally coupled to the lift arm  106 . In particular, the lift mast  104  comprises a bracket  150  to which the motor  110  of the lift actuator  204  is attached while the actuator arm  114  is pivotally coupled to the lift arm  106  at the actuator pivot  140 . Accordingly, it should be understood that, by actuating the lift actuator  204  with the motor  110 , the actuator arm  114  is extended or retracted thereby raising or lowering the lift arm  106  relative to the base  102 . In one embodiment, the lift actuator  204  may further comprise an emergency release  112 . The emergency release facilitates the manual retraction of the actuator arm  114  in the event of a mechanical or electrical malfunction of the lift actuator  204 . 
     Still referring to  FIGS.  1 A and  1 B , the lifting device  100  may further comprise a control unit  202 . The control unit  202  may comprise a battery  146  and may be electrically coupled to the lift actuator  204  and the base actuator  206  and also to the upper limit switch (not shown) and the lower limit switch (not shown). The control unit  202  may be operable to receive an input from an operator via a control device coupled to the control unit  202 . The control device may comprise a wired controller and/or one or more wireless controllers. For example, in one embodiment, the control device may be a wired controller or, alternatively, a controller integrated into the control unit  202 . In another embodiment, the controller may be a wireless controller such as a wireless hand control and/or a wireless diagnostic monitor/control. Based on the input received from the control device, the control unit is programmed to adjust the position of the lift arm  106  and/or the position of the base legs  108 A,  108 B by sending electric control signals to the lift actuator  204  and/or the base actuator  206 . Further, as will be described in more detail herein, the control unit  202  may also be incorporated into a lift control system for the lifting device  100 . The lift control system may be used to monitor lift performance and determine when service on the lifting device is required and when use of the lifting device  100  should be discontinued. 
     It should be understood that, the term “service,” as used herein, refers to the inspection, maintenance or replacement of a structural component of the lifting device or an electrical component of the lifting device. Further, it should also be understood that the phrase “structural component” refers to the mechanical and structural components of the lifting device including, without limitation, the lift arm, the mast support, the lift mast, the base, the cross support, the base leg, the base leg pivot, the front castors, the rear castors, the castor brakes, the lift mast adjustment handle and associated fastener, the lift arm pivot, the actuator pivot, the attachment coupling, the attachment pivot, the bracket of the lift mast and/or combinations thereof. It should also be understood that the phrase “electrical component” refers to the lift actuator, the base actuator, the various components of the lift control system, and/or various components thereof. 
     While the embodiments described herein refer to the lift actuator  204  as comprising a motor  110  and an actuator arm  114 , it will be understood that the actuator may have various other configurations and may include a hydraulic or pneumatic actuator comprising a mechanical pump or compressor or a similar type of actuator. Further, in other embodiments, where the lifting device is a cable-based lift system, the actuator may be a motor which pays out and/or takes-up cable thereby raising and/or lowering an attached load. Accordingly, it will be understood that various other types of actuators may be used to facilitate raising and lowering the lift arm and/or an attached load with respect to the base  102 . 
     Moreover, while  FIGS.  1 A and  1 B  depict the lifting device  100  as a mobile patient lift, it should be understood that the lift control systems described herein may be used in conjunction with other lifting devices having various other configurations including, without limitation, stationary lifting devices and overhead lifting devices. Further, it should also be understood that, while specific embodiments of the lifting device described herein relate to lifting devices used for raising and/or lowering patients, the lift control systems described herein may be used with any lifting device which is operable to raise and lower a load. 
     The lift control system  200  of the lifting device  100  will now be described in more detail with reference to  FIGS.  1 - 4   . 
     Referring now to  FIG.  2   , a block diagram of a lift control system  200  for use in conjunction with the lifting device  100  shown in  FIGS.  1 A and  1 B  is schematically depicted according to one or more embodiments shown and described herein. The lift control system  200  may generally comprise a control unit  202 , and a control device such as, for example, a wired controller  212  and/or a wireless controller, such as a wireless hand control  210  and/or a wireless diagnostic monitor/control  208 . In one embodiment, the lift control system  200  may also include the battery  146  and/or one or more indicators. In the embodiment shown in  FIG.  2   , the lift control system  200  comprises four indicators  203 A- 203 D. 
     The control unit  202  may generally comprise a central processing unit (“CPU”) and associated electrical components, including, without limitation, a processor (not shown) and at least one memory (not shown). The memory includes a set of computer readable and executable instructions which the processor executes to control the lifting device. Utilizing the computer readable and executable instructions, the control unit  202  is operable to output a control signal to the lift actuator  204  and/or the base actuator  206  based on input signals received from the wireless hand control  210 , the wired controller  212 , and/or the diagnostic monitor/control  208 . 
     The one or more indicators provide an operator of the lifting device  100  with an indication of the status of various components and/or systems of the lifting device. In one embodiment, the at least one indicator comprises a visual indicator such as an LED or similar lamp capable of providing an operator with a visual indication. Alternatively, the at least one indicator may comprise an audible indicator, such as a speaker or similar device capable of producing an audible signal. 
     In one embodiment, the first indicator  203 A may be indicative of the control unit communicating with a wireless controller, such as the wireless hand control  210  or the diagnostic monitor/control  208 . When the indicator is activated, the control unit  202  is receiving a signal from the wireless controller and/or sending a signal to the wireless controller. 
     The second indicator  203 B may be indicative of an overload condition in the lift actuator, such as when the load on the lifting device  100  exceeds a pre-programmed load limit, as will be described in more detail herein. 
     The third indicator lamp may be indicative of the lifting device  100  requiring service. As described further herein, the service interval may be based on time and/or usage of the lifting device and constant values may be pre-programmed in the control unit such that, when the lifting device exceeds the pre-programmed limit, the service indicator is activated. 
     The fourth indicator  203 D may be indicative of the Expected Life Time (ELT) of the lifting device. For example, the lifting device  100  may have a predetermined life expectancy based on time and/or usage and, when this value is approached and/or exceeded, the control unit activates the indicator. 
     The control unit  202  may further comprise at least one port for sending and/or receiving signals from other devices in the lift control system  200 . For example, in one embodiment, the control unit  202  comprises at least one transceiver, such as an infrared (IR) transceiver or a radio frequency (RF) transceiver, which may be utilized by the control unit  202  to send data signals to other components in the lift control system  200 . In the embodiments shown and described herein, the control unit  202  of the lift control system  200  comprises an IR transceiver which is operable to send data signals to and receive data signals from the diagnostic monitor/control  208  and/or the wireless hand control  210 . 
     As described herein, the control unit  202  may be coupled to a control device such as wired controller  212 , wireless hand control  210 , and/or diagnostic monitor/control  208 . The wired controller  212  may be integral with the control unit  202  while, in other embodiments, the wired controller  212  may be coupled to the control unit  202  with a cable. In the embodiments shown and described herein, the wired controller  212  is integral with the control unit  202 . The wireless hand control  210  and the diagnostic monitor/control  208  include IR or RF transceivers such that the wireless hand control  210  and/or the diagnostic monitor/control  208  are operable to send signals to, and receive signals from, the control unit  202 . 
     Each of the wired controller  212 , the wireless hand control  210  and the diagnostic monitor/control  208  comprise user input controls located on the control device which may be used to control the lifting device. For example, referring to the wireless hand control  210  depicted in  FIG.  3    and the diagnostic monitor/control  208  depicted in  FIG.  4   , each of the control devices comprise user input controls, such as buttons  218 - 230 , which may be used to operate the lifting device  100 . The user input controls may include buttons  228 ,  230  (designated by large up and down arrows) which may be used to rapidly raise and lower the lift arm  106  of the lifting device  100 , buttons  218 ,  220  (designated by small arrows) which may be used to more slowly raise and lower the lift arm  106  of the lifting device, and buttons  222 ,  224  (with designations resembling a “V” and a “U”) which may be used to pivot the base legs  108 A,  108 B relative to the lift mast  104 . While specific reference has been made herein to the wireless hand control  210  and the diagnostic monitor/control  208 , it should be understood that the wired controller  212  contains similar user input controls. 
     Still referring to  FIG.  2   , the control unit  202  may also comprise one or more ports for communicatively connecting the control unit  202  to an external computer  300  or computer system to facilitate downloading data from the control unit  202 , uploading data to the control unit  202 , and/or reprogramming the control unit  202 . For example, the control unit may comprise a USB port, an RS-232 port, an IR port or a similar port to facilitate directly coupling the control unit  202  to a computer  300  or computer system. In this embodiment, the processor of the control unit  202  executes the computer readable and executable instruction set stored in the memory to upload at least one operating characteristic of the lifting device and/or at least one accumulated operating parameter to the external computer system. The phrase “operating characteristic,” as used herein, includes, without limitation, a load applied to the lift arm, a current supplied to the actuator, an operation time of the lifting device, a current discharged from the battery of the lift control system, a power discharged from a battery of the lift control system or combinations thereof. The phrase “accumulated operating parameter,” as used herein, includes, without limitation, an accumulated number of initiated battery charging events, an accumulated number of incomplete battery charging events, an accumulated number of battery replacements, an accumulated load-time parameter, an accumulated current-time parameter, an accumulated power-time parameter, an accumulated number of upper end positions of the lift actuator, an accumulated number of lower end positions of the lift actuator, an accumulated number of overload stops of the lifting device, an average current consumption of the lifting device, an accumulated operating time of the lifting device, an accumulated operating time of the lifting device, an accumulated number of starts of the lifting device, or combinations thereof. The processor of the control unit  202  also executes the computer readable and executable instruction set stored in the memory to download service constants and/or operational parameters of the lifting device from the external computer system when the lift control system is communicatively coupled to the external computer system. 
     In the embodiments where the control unit comprises a battery  146 , as depicted in  FIG.  2   , the control unit  202  also comprises circuitry to charge the battery when the lifting device, specifically the lift control system  200  of the lifting device, is coupled to a voltage source (i.e., when the lift control system is plugged in to a wall outlet or other source for supplying power to the lift control system). In one embodiment, the memory of the control unit  202  also comprises computer readable and executable instructions for monitoring an accumulated number of initiated battery charging events, an accumulated number of completed battery charging events and an accumulated number of incomplete battery charging events and storing each of these quantities in the memory of the control unit  202 . The control unit  202  also comprises circuitry and the memory of the control unit comprises corresponding computer readable and executable instructions for monitoring when the battery  146  has been replaced and storing the time of replacement and the accumulated number of battery replacements in the memory. 
     In the embodiments described herein, the control unit  202  also comprises circuitry and the memory of the control unit comprises corresponding computer readable and executable instructions for regulating and measuring the current supplied to the lift actuator  204  and the base actuator  206  by the lift control system  200 . For example, the control unit  202  may contain circuitry which functions as an ammeter for monitoring the magnitude of the current supplied to either the lift actuator  204  or the base actuator  206 . The control unit  202  may monitor the magnitude of the current and store the value of the supplied current in the memory of the control unit. In one embodiment, the memory of the control unit comprises computer readable and executable instructions for monitoring the power and/or current discharged by the battery and storing these values in memory. The control unit  202  may also be programmed to determine the average current consumption of the lifting device over a specified interval and store the value in memory. 
     The control unit  202  may also comprise computer readable and executable instructions for monitoring and/or preventing overload conditions during operation of the lift. For example, the control unit  202  may be programmed to monitor the current supplied to the lift actuator  204  when the lifting device is actuated with the control device as described above. The control unit  202  compares the current supplied to the lift actuator  204  to a predetermined current threshold value stored in the memory of the control unit. When the current supplied to the lift actuator  204  exceeds the current threshold value, the control unit  202  discontinues the current supplied to the lift actuator, thereby stopping the lifting device, and provides an indication, such as with indicator  203 B, that the current supplied to the lift actuator has exceeded the current threshold value. The control unit may also be programmed to store the accumulated number of overload stops in the memory of the control unit. 
     The control unit  202  of the lift control system  200  may also comprise computer readable and executable instructions for timing various parameters relating to the operation of the lifting device and storing such parameters in the memory of the control unit  202 . In one embodiment, the control unit  202  may comprise computer readable and executable instructions for storing the number of times the lifting device is started. For example, the control unit  202  logs a starting event each time the lifting device is started and continuously operated for a predetermined time period. The control unit  202  maintains a count of the accumulated number of starts in the memory of the control unit. Similarly, the control unit also maintains the accumulated operating time of the lifting device in the memory of the control unit. In one embodiment, the control unit maintains the total accumulated operating time of the lifting device as accrued over the entire lifetime of the lifting device and/or the periodically accumulated operating time of the lifting device as accrued between consecutive service events. The control unit  202  may also be programmed to monitor the elapsed calendar time between service events in addition to the total number of service events performed. 
     In another embodiment, the control unit  202  is programmed with computer readable and executable instructions for receiving and processing input signals from one or more sensors, such as the upper limit switch  214  and the lower limit switch  216 . When the actuator arm  114  is fully extended (e.g., when the actuator arm has reached its maximum amount of travel), the upper limit switch  214  is triggered which, in turn, sends a signal to the control unit  202  indicating that the actuator arm  114  is fully extended and has reached an upper end position. The control unit  202  tracks each time the upper limit switch  214  is actuated (i.e., the number of upper end positions) and stores the accumulated number of upper end positions in memory. Similarly, when the actuator arm  114  is fully retracted, the lower limit switch  216  is triggered which, in turn, sends a signal to the control unit  202  indicating that the actuator arm  114  is fully retracted has reached a lower end positions. The control unit  202  tracks each time the lower limit switch  216  is actuated and stores the accumulated number of lower end positions in memory. Accordingly, based on the signals provided by the upper limit switch  214  and the lower limit switch  216 , the control unit  202  determines when the actuator arm  114  has reached either extreme of its range of travel (e.g., fully extended or fully retracted). 
     Alternatively or additionally, the control unit  202  is programmed with computer readable and executable instructions for receiving and processing input signals from a load sensor (not shown) mechanically coupled to the lift arm of the lifting device. The load sensor may comprise a load cell, a linear varying displacement transducer (LVDT) or a similar sensor operable to detect a load applied to the lift arm of the lifting device and output an electrical signal indicative of that load to the control unit. The control unit  202  is programmed to determine the load applied to the lift arm based on the signal received from the load sensor and track the time that the load is applied to the lift arm. 
     The computer readable and executable instructions stored in the memory of the control unit  202  of the lift control system  200  may be executed by the processor to determine when a structural component of the lifting device or an electrical component of the lifting device is in need of service. More specifically, the lift control system  200  may be operable to determine when structural components and/or electrical components of the lifting device are in need of inspection and maintenance, when structural components and/or electrical components of the lifting device are in need of replacement, and/or when the lifting device has reached the end of its usable life. The operation of the lifting device  100  and the lift control system  200  of the lifting device for determining when the lifting device is in need of service will be described in more detail with respect to  FIGS.  1 A,  1 B and  2   . 
     Referring to  FIGS.  1 A,  1 B and  2   , when the lifting device  100  is actuated with one of the control devices, the lift control system  200  outputs a control signal from the control unit  202  to the lift actuator  204  which actuates the lift actuator  204  thereby causing the lift arm  106  to be raised or lowered with respect to the base  102 . As the lift arm  106  is raised or lowered, the control unit  202  determines the operating time of the lifting device  100  and stores the operating time of the lifting device  100  in the memory of the control unit  202 . At the same time the control unit  202  also determines at least one operating characteristic of the lifting device  100  while the lift arm  106  is being raised or lowered and stores this operating characteristic in the memory of the control unit  202 . The operating characteristic may include a load applied to the lift arm  106 , a current supplied to the lift actuator  204 , an operation time of the lifting device  100 , a current discharged from the battery  146  of the lift control system  200 , or a power discharged from a battery  146  of the lift control system  200 , as described hereinabove. For example, in one embodiment described herein, the operating characteristic is the current supplied to the lift actuator  204  as the lift arm  106  is raised or lowered, the power discharged by the battery  146  as the lift arm  106  is raised or lowered, or the current discharged by the battery  146  as the lift arm  106  is raised or lowered. More specifically, the current of the control signal varies with the load (i.e., the mass) applied to the lift actuator  204  via the lift arm  106 . For example, when a load is present on the attachment accessory  136 , such as when a sling or other device attached to the attachment accessory  136  contains a patient, the current supplied to the lift actuator  204  to raise the lift arm  106  may be greater than when no load is present on the lift arm  106 . Accordingly, it will be understood that the current supplied to the lift actuator  204  may be in direct proportion to the weight or load that the lift arm  106  and lifting device  100  are subjected to and, as such, the current supplied to the lift actuator  204  may be used as an indicator of the weight or load on the lifting device  100 . The current supplied to the lift actuator  204  may be determined based on the current supplied to the lift actuator  204  during actuation of the lifting device  100 , the power discharged in the battery  146  during actuation of the lifting device  100 , or the current discharged by the battery  146  during actuation of the lifting device  100 . The current and/or power may be stored in the memory of the control unit  202 . 
     In an alternative embodiment, the at least one operating characteristic is the load applied to the lift arm  106  as measured by the load sensor mechanically coupled to the lift arm  106 . In this embodiment, the load sensor outputs a signal indicative of the load applied to the control unit  202  which stores the value in memory. 
     After the at least one operating characteristic and the operating time have been determined and stored in the memory of the lifting device  100 , the control unit  202  determines an accumulated operating time for the lifting device by adding the determined valued for the operating time to the previously accumulated operating time of the lifting device and storing the accumulated operating time of the lifting device in the memory of the control unit. The accumulated operating time may be the operating time accumulated since the last service event (i.e., a periodically accumulated operating time) and/or the operating time accumulated over the entire life of the lifting device (i.e., a total accumulated operating time). 
     An accumulated load-time parameter of the lifting device is also determined based on the at least one operating characteristic and the operating time of the lifting device. For example, the determined operating characteristic may be the load applied to the lift arm  106  and the load-time parameter is determined by multiplying the load by the time of operation of the lifting device and adding the product to a previously determined accumulated load-time parameter stored in the memory of the control unit. Alternatively, the operating characteristic may be the current supplied to the lift actuator  204  as the lift arm  106  is raised or lowered, the power discharged by the battery  146  as the lift arm  106  is raised or lowered, or the current discharged by the battery  146  as the lift arm is raised or lowered. In this embodiment, the accumulated load-time parameter is determined by multiplying the current or power by the operating time of the lifting device and adding the product to a previously determined accumulated load-time parameter stored in the memory of the control unit. The newly determined accumulated load-time parameter is then stored in the memory of the control unit. The accumulated load-time parameter may be a periodically accumulated load-time parameter (i.e., the load-time parameter accrued since the last service event) and/or the accumulated load-time parameter (i.e., the load-time parameter accrued over the entire life of the lifting device). 
     In one embodiment, after the accumulated operating parameter is determined, the lift control system compares the accumulated operating parameter to a predetermined service constant stored in the memory of the lifting device to determine if a structural component of the lifting device is in need of service. In one embodiment, the comparison between the accumulated operating parameter and the service constant is utilized to determine if a structural component of the lifting device requires inspection or maintenance. In this embodiment, the accumulated operating parameter is a periodically accumulated operating parameter and the service constant is a service load-time interval. For example, the service load-time interval may be a predetermined load-time value which is indicative of when structural components of the lifting device need service. If the service load-time interval is greater than the periodically accumulated operating parameter, no inspection or maintenance is needed. However, if the service-load time interval is less than or equal to the periodically accumulated operating parameter, inspection and maintenance of at least one structural component of the lifting device is required and the control unit  202  activates the third indicator lamp  203 C (i.e., the maintenance indicator) thereby indicating to a user that the lift is in need of inspection and/or maintenance. 
     The comparison between the accumulated operating parameter and the service constant may also be utilized to determine if a structural component of the lifting device needs to be replaced. In this embodiment, the accumulated operating parameter is a total accumulated load-time interval and the service constant is indicative of a replacement load-time interval of at least one structural component of the lifting device. For example, each structural component of the lifting device may have an associated replacement load-time interval which generally corresponds to a predetermined percentage of the useable service life of the structural component. If the replacement load-time interval is greater than the total accumulated operating parameter, none of the structural components of the lifting device need to be replaced. However, if the replacement load-time interval is less than or equal to the total accumulated operating parameter of the lifting device at least one structural component of the lifting device requires replacement and the control unit  202  activates the third indicator  203 C (i.e., the maintenance indicator) thereby indicating to a user that at least one structural component of the lifting device is in need of inspection and/or maintenance. To differentiate from the embodiment described above wherein illumination of the maintenance indicator lamp indicates the need for inspection and maintenance of a structural component of the lifting device, the control unit may activate the indicator differently for each set of circumstances. For instance, where the indicator is an LED, the indicator may be activated to flash when a structural component of the lifting device is in need of service or maintenance and the indicator may be constantly illuminated when one or more structural components of the lifting device are in need of service. 
     The comparison between the accumulated operating parameter and the service constant may also be utilized to determine if the lifting device has reached the end of its usable service life. In this embodiment, the accumulated operating parameter is a total accumulated load-time interval and the service constant is indicative of a usable service life of the lifting device. For example, the lifting device  100  may have a predetermined service life and the usable service life may be indicative of a predetermined percentage of the service life. If the usable service life is greater than the total accumulated operating parameter, the lifting device  100  may remain in operation. However, when the total accumulated operating parameter reaches a predetermined percentage of the usable service life, the lift control system  200  of the lifting device may activate the fourth indicator  203 D. For example, when the fourth indicator is an LED, the lift control system  200  may cause the fourth indicator to flash indicating that the total accumulated operating parameter has reached a predetermined percentage of the usable service life of the lifting device  100 . When the total accumulated operating parameter is greater than or equal to the usable service life, the lift control system  200  of the lifting device activates the fourth indicator  203 D. For example, when the fourth indicator is an LED, the lift control system  200  causes the fourth indicator  403  to remain illuminated indicating that the total accumulated operating parameter has reached and/or exceeded the usable service life of the lifting device  100  and that use of the lifting device should be discontinued. Additionally, when the total accumulated operating parameter is greater than or equal to the usable service life, the lift control system  200  of the lifting device may prevent further operation of the control device. 
     While specific embodiments described herein relate to the inspection, maintenance and/or replacement of lift structural components, it should be understood that similar procedures may be used in conjunction with service constants related to the use of electrical components of the lift to determine when the electrical components of the lift require inspection, maintenance and/or replacement. 
     In addition to comparing the accumulated operating parameter to the service constant to determine when the lifting device is in need of service, the lift control system also compares the periodically accumulated operating time of the lifting device to an operating time service constant. The operating time service constant is indicative of a maximum time period between service intervals. If the periodically accumulated operating time of the lifting device is greater than or equal to the operating time service constant, the lifting device is in need of service and the lift control system  200  illuminates the third indicator  203 C. Where the third indicator  203 C is an LED, as described above, the third indicator  203 C may be made to flash in a particular pattern to indicate that the periodically accumulated operating time has exceeded the operating time service constant. 
     When the third indicator  203 C is activated, the lifting device  100  may be serviced by a technician who performs the required inspection, maintenance and/or replacement of structural components as needed. Where the fourth indicator  203 D is activated, the lifting device  100  may also be serviced. However, when the fourth indicator  203 D is activated, the service may be more extensive and may include a complete overhaul or refurbishment of the lifting device. Regardless of the type of service performed, the date of the service event may be entered into the memory of the control unit and the control unit may update the total accumulated number of service events that have been performed on the lifting device. Additionally, the type of service performed as well as an indication of any structural components that have been repaired and/or replaced may also be saved in the memory of the control unit. Accordingly, it should be understood that a service record may be saved in the memory of the lift control system of the lifting device and that service record accompanies the lifting device throughout its lifetime. 
     As described hereinabove, the lift control system  200  of the lifting device  100  may comprise a wireless diagnostic monitor/control  208 . In addition to providing user inputs to control the functionality of the lifting device, the diagnostic monitor/control  208  may comprise a processor and a memory having computer readable and executable instructions which enable the diagnostic monitor/control to be utilized as a diagnostic tool for servicing and maintaining the lifting device  100 . In one embodiment the diagnostic monitor/control  208  is programmed to send data to and receive data from the control unit  202 . For example, the data sent to the control unit comprises at least one operational parameter (i.e., the current threshold limit or a similar parameter) and/or at least one service constant such as, for example, the service time interval, the replacement interval of at least one structural component and/or the usable service life of the lifting device. The operational parameters and/or service constant may be stored in a memory operatively associated with the control unit  202 . The data received by the diagnostic monitor/controller from the control unit  202  comprises at least one operating characteristic and/or an accumulated operating parameter of the lifting device. The operating characteristic and/or accumulated operating parameter is stored in a memory operatively associated with the diagnostic monitor/control  208 . An operator or service technician may retrieve the at least one operating characteristic and/or accumulated operating parameter from the diagnostic monitor/control  208  and/or otherwise review the at least one operating parameter and/or accumulated operating parameter on the display  234  of the diagnostic monitor/control  208 . 
     Further, the computer readable and executable instruction set stored in the diagnostic monitor/control  208  may be executed by the processor of the diagnostic monitor/control  208  to reset various service and/or life parameters stored in the controller. For example, when the service indicator (i.e., the third indicator described above) is illuminated, thereby indicating that the lifting device  100  requires service, the diagnostic monitor/control  208  may be used to reset the service lamp and restart the service interval. Further, when the ELT indicator (i.e., the fourth indicator described above) is illuminated, thereby indicating that the lifting device  100  has reached or is approaching the predetermined service life expectancy, the diagnostic monitor/control  208  may be operable to reset the service ELT indicator and restart the ELT counter following refurbishment of the lifting device. Accordingly, it will be understood that the diagnostic monitor/control  208  may be used reset various parameters associated with the operation and maintenance of the lifting device. 
     In another embodiment, the computer readable and executable instruction set stored in the memory of the control unit  202  and/or in the diagnostic monitor/control  208  may be executed to upload at least one accumulated operating parameter and/or the operating characteristic to a computer  300 , network, or other, similar data storage device, where the at least one accumulated operating parameter and/or the operational characteristic are stored in a history file unique to the specific lifting device  100 . For example, in one embodiment, the history file is correlated to the serial number of the lifting device and/or the identification number of the controller which is stored in the memory of the control unit  202 . In one embodiment, the history file may be accessed remotely, such as over an internet or similar network connection, and an operator or technician may utilize the data stored in the history file to perform diagnostics on the particular lifting device  100 . For example, the at least one accumulated operating parameter and/or the operational characteristic may be analyzed to determined if the lifting equipment is suitable for the conditions of use (e.g., loads, height of lifts, total power consumption, etc.) under which the lift is being used. For example, if the history file of the lifting device indicates that the number of upper end positions is abnormally high, the lifting device may not have the desired vertical range of motion. Accordingly, the lift mast  104  of the lifting device  100  may need to be raised. Similarly, if the number of overload stops is high, the lifting device  100  may not be suitable for the loads being applied to the lifting device  100  and an alternative lifting device and/or actuator may be recommended. Further, the history file may be utilized to determine if the lifting device  100  is being properly used by reviewing the number of overloads, the charging history, the number of batteries used, the total number of starts and actuator drive time as well as the total actuator drive time and calendar time since the last reset. The history file may also be utilized to track the lift through service records which may be associated with the serial number of the lifting device  100 . In addition, the history file may also be used to determine if either the structural components or the electrical components are in need of service and/or replacement. 
     In addition to functioning as a controller for the lifting device  100  and/or a diagnostic tool for maintaining the lifting device  100 , the diagnostic monitor/control may also be used to instantaneously access operating data stored in the control unit  202  of the lifting device. For example, the diagnostic monitor/control  208  may also be operable to accumulated operating parameters stored in the memory of the control unit. Such information may be instantaneously available to a technician or salesperson to determine if the lifting device is in need of service, requires spare or replacement parts, or if a different model of lifting device may be more suitable for the operator&#39;s needs. 
     It should now be understood that the lift control system shown and described herein may be used in conjunction with a lifting device to assess the suitability of the equipment for use in conjunction with the specific operational conditions as well as to determine the proper maintenance and repair intervals for the lifting device. Further, the lift control system shown and described herein provides a system by which operating and service parameters may be easily and readily accessed and tracked throughout the life of the lifting device. 
     It should also be understood that the use of a periodically accumulated load-time parameter facilitates servicing the lifting device according to usage rather than servicing the lifting device according to time. For example, lifting devices which are used more frequently will be serviced more often than lifting devices that are used less frequently. Accordingly, use of the periodically accumulated load-time parameter to determine when the lifting device needs to be serviced permits flexibility in servicing the lifting device and allows the lifting device to be serviced as needed rather than according to a rigid maintenance schedule. This may result in reduced device down time due to preventative maintenance in cases where the lifting device is frequently used and reduced maintenance costs where devices are used less frequently. 
     While the specific embodiments described herein relate to a mobile lifting device comprising an actuator and a lift arm, it should be understood that the basic principle of operation of the lift control system may be applied to lifting devices having various other configurations. 
     While particular embodiments and aspects of the present invention have been illustrated and described herein, various other changes and modifications can be made without departing from the spirit and scope of the invention. Moreover, although various inventive aspects have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of this invention.