Patent Publication Number: US-10315896-B2

Title: Electric winch device

Description:
TECHNICAL FIELD 
     The present invention relates to an electric winch device for use in a crane. 
     BACKGROUND ART 
     Conventionally known as a winch device mounted on a crane for conducting hoisting work (crane work) is an electric winch device driven by an electric motor to raise an object for hoisting work. Then, a known electric winch device is provided with a regeneration function of converting, during the lowering of an object, kinetic energy generated due to the moving-down of the object into electric energy and recovering the same. Patent Literature 1 set forth below discloses one example of an electric winch device provided with such a regeneration function. 
     The electric winch device disclosed in Patent Literature 1 is provided with a motor as an electric motor, and electricity storage means which stores regenerative power generated in the motor during the lowering. The motor is configured to be driven by at least one of electric power supplied from the electricity storage means and electric power supplied from a commercial power source to operate a crane. 
     Some movable cranes use an electric winch device capable of conducting a moving-down of an object, in which the object is lowered in a state close to the free-fall. When such an electric winch device is provided with the regeneration function as described above, at the time of the free-fall of the object, electric power is regenerated by an electric motor and the regenerated electric power is consumed through storage of electricity in an electricity storage device, resulting in generating a braking force in the electric motor. The braking force generated in the electric motor brakes rotation of a winch drum in a lowering direction, resulting in braking the free-fall of the object. 
     However, when a fail such as a short-circuit develops in any part of an electric system leading from the electricity storage device to the electric motor, electric power regenerated by the electric motor is not consumed, so that no braking force is obtained by regeneration. Although an allowable stopping height is set as a height of a lowest position at which the object is required to be stopped by braking operation, at the time of the free-fall of the object, when no braking force is obtained by regeneration as described above, the object might move down to a position at a height lower than the allowable stopping height. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2007-166775 
     SUMMARY OF INVENTION 
     The present invention aims to prevent an object, at the time of a free-fall of the object, from moving down to a position at a height lower than an allowable stopping height even when a fail develops in an electric system leading from a regenerative power consumption unit such as an electricity storage device to an electric motor, in an electric winch device of a crane provided with a regeneration function. 
     An electric winch device according to one aspect of the present invention is an electric winch device provided in a crane for raising and lowering an object, the electric winch device comprising: an electric motor; a winch drum driven by the electric motor to rotate for raising of the object; a braking device which brakes rotation of the winch drum; a braking operation part to be operated for stopping moving-down of the object; a regenerative power consumption unit which consumes at least a part of regenerative power regenerated by the electric motor at the moving-down of the object to cause the electric motor to generate a braking force on the rotation of the winch drum; a setting unit for setting an allowable stopping height which is a height of a lowest position at which the object is required to be stopped at a time of a free-fall of the object; an operational braking force estimation section which estimates an operational braking force which is a braking force according to an operation amount of the braking operation part; a required braking force estimation section which estimates a required braking force which is a braking force required to stop the free-falling object at a position at the allowable stopping height set by the setting unit; a braking force determination section which determines, out of the operational braking force, each of a first braking force to be borne by the braking device and a second braking force to be borne by a braking force which is generated in the electric motor due to consumption of the regenerative power; and a control section which causes the braking device to apply the first braking force, which has been determined by the braking force determination section, to the winch drum, wherein the braking force determination section determines the first braking force to be a braking force equal to or greater than the required braking force when, at a time of stopping of the free-falling object, the operational braking force estimated by the operational braking force estimation section is equal to or greater than the required braking force estimated by the required braking force estimation section. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a configuration of an electric winch device according to one embodiment of the present invention. 
         FIG. 2  is a functional block diagram showing a detailed internal configuration of a controller in the electric winch device shown in  FIG. 1 . 
         FIG. 3  is a diagram showing operation amount-braking force characteristics as a correlation between an operation amount of a brake pedal and a braking force to be applied to a winch drum according to the operation amount. 
         FIG. 4  is a flow chart showing operation of the electric winch device at the time of braking a free-fall of an object. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     In the following, an embodiment of the present invention will be described with reference to the drawings. 
     First, with reference to  FIG. 1  to  FIG. 3 , a configuration of an electric winch device according to one embodiment of the present invention will be described. 
     The electric winch device according to the present embodiment is provided in a crane for use as a winch device for a hoisting load which conducts raising/lowering of a hoisting load  100 . The crane provided with the electric winch device of the present embodiment includes a boom  2  (see  FIG. 1 ) provided in a crane main body not shown so as to be capable of derricking. At a distal end of the boom  2 , a top sheave  3  is provided. From the distal end of the boom  2 , a hook device  6  is suspended via a hoisting rope  4  which is a wire rope. The hook device  6  includes a hook sheave not shown. The hoisting rope  4  is wound around the hook sheave and the top sheave  3  a predetermined number of times. The hoisting load  100  is hung by the hook device  6 . Hereinafter, the hook device  6  and the hoisting load  100  hung therefrom will be integrally referred to as an object  102  to be raised/lowered. The electric winch device is mounted on the crane main body not shown to conduct raising/lowering of the object  102  via the hoisting rope  4 . 
     In the following, a specific configuration of the electric winch device according to the present embodiment will be described. 
     The electric winch device according to the present embodiment is configured to be able to conduct a moving-down of the object  102 , in which the object  102  is lowered in a state close to a free-fall as will be described later. Additionally, the electric winch device according to the present embodiment is provided with a regeneration function of converting kinetic energy caused by the moving-down of the object  102  into electric power and recovering the same. This electric winch device, as shown in  FIG. 1 , includes a drum  12 , an electric motor  14 , a decelerator  16 , an inverter  20 , a regenerative power consumption unit  22 , a braking device  24 , an operation lever device  26 , a brake pedal device  28 , a controller  30 , a load meter  32 , a drum rotation meter  36 , and a setting unit  38 . 
     The drum  12  is a winch drum driven by the electric motor  14  to rotate for raising/lowering of the hook device  6  and the hoisting load  100  hung therefrom. In the following, the hook device  6  and the hoisting load  100  hung therefrom will be integrally referred to as the object  102  to be raised/lowered. The drum  12  takes up the hoisting rope  4  by rotation thereof in a raising direction which is one rotation direction, thereby raising the object  102 . Additionally, the drum  12  draws out the hoisting rope  4  by rotation thereof in a lowering direction which is a rotation direction reverse to the raising direction, thereby lowering the object  102 . At the time of the free-fall of the object  102 , the drum  12  freely rotates in the lowering direction to cause the object  102  to move down. 
     The electric motor  14  is supplied with electric power to operate to rotate the drum  12  in the raising direction. The electric motor  14  functions as a power generator at the time of lowering of the object  102 , i.e. when the drum  12  rotates in the lowering direction. A driving shaft  14   a  of the electric motor  14  is coupled to a rotation shaft  12   a  of the drum  12  via the decelerator  16 . At the time of raising of the object  102 , a driving torque of the electric motor  14  is transmitted from the driving shaft  14   a  to the drum  12  via the decelerator  16  and the rotation shaft  12   a , thereby rotating the drum  12  in the raising direction. At the time of the lowering and the free-fall of the object  102 , rotation of the drum  12  in the lowering direction is transmitted from the rotation shaft  12   a  to the electric motor  14  via the decelerator  16  and the driving shaft  14   a , so that the electric motor  14  generates power. Thus, regeneration is conducted in which kinetic energy caused by the moving-down of the object  102  is converted into electric energy and recovered. The decelerator  16  slows down rotation of the driving shaft  14   a  of the electric motor  14  at a predetermined reduction ratio and transmits the resultant rotation to the rotation shaft  12   a  of the drum  12 . 
     The inverter  20  controls operation of the electric motor  14  in response to a command from the controller  30 . Specifically, the inverter  20  controls the number of rotations and an amount of rotation of the electric motor  14  by changing an amount of current to be supplied to the electric motor  14  according to the command from the controller  30 , thereby controlling a raising speed and a raising amount of the object  102 . 
     The regenerative power consumption unit  22  is electrically connected to the electric motor  14  via the inverter  20 . The regenerative power consumption unit  22  consumes at least a part of regenerative power regenerated by the electric motor  14 . Specifically, the regenerative power consumption unit  22  is a storage battery which consumes regenerative power regenerated by the electric motor  14  by storing the power. As the regenerative power consumption unit  22 , a combination of a storage battery and a regenerative resistor which consumes regenerative power that cannot be stored in the storage battery may be used. The regenerative power consumption unit  22  supplies the stored electric power to the electric motor  14  via the inverter  20 . Consumption, by the regenerative power consumption unit  22 , of the regenerative power regenerated by the electric motor  14  leads to generation of a braking force in the electric motor  14 . Braking the rotation of the drum  12  by thus generated braking force in the electric motor  14  is referred to as regenerative braking. 
     The braking device  24  is a mechanical braking device to conduct operation of braking rotation of the drum  12  in the raising direction and the lowering direction. The braking device  24  brakes the drum  12  in response to a control signal from the controller  30 , as well as applying, to the drum  12 , a braking force designated by the control signal from the controller  30 . As the braking device  24 , a mechanical brake, a hydraulic clutch or the like is used. 
     The operation lever device  26  is used by an operator to instruct raising/lowering operation of the object  102  by the electric winch device. The operation lever device  26  includes a lever  26   a  operated by an operator to instruct rotation of the drum  12  in the raising direction; rotation of the drum  12  in the lowering direction; or stop of the rotation of the drum  12 . The lever  26   a  is operable to a raising side as one side from a neutral position at which an instruction to stop the rotation of the drum  12  is issued and operable to a lowering side as the other side (opposite to the raising side) from the neutral position, the raising side being a side to which an instruction to rotate the drum  12  toward the raising direction of the object  102  is issued, and the lowering side being a side to which an instruction to rotate the drum  12  toward the lowering direction of the object  102  is issued. The operation lever device  26  outputs, to the controller  30 , information indicative of an operation direction and an amount of operation from the neutral position of the lever  26   a.    
     The brake pedal device  28  is a device which outputs, to the controller  30 , a command for stopping the moving-down of the object  102  at the time of the free-fall of the object  102 . The brake pedal device  28  includes a brake pedal  28   a  operated by an operator for stopping the moving-down of the object  102 . The brake pedal  28   a  is one example of a braking operation part according to the present invention. In the following, the brake pedal  28   a  will be simply referred to as the pedal  28   a . The brake pedal device  28  outputs a signal indicative of an operation state of the pedal  28   a  to the controller  30 . Specifically, the pedal  28   a , in a state of not being operated by an operator, i.e. in a state of not being depressed, is placed at a reference position at which the pedal rises highest. In this state, the brake pedal device  28  outputs a signal indicating that the operation amount of the pedal  28   a  is 0 to the controller  30 . Then, when the pedal  28   a  is operated (depressed) from the reference position by the operator, the brake pedal device  28  outputs, to the controller  30 , a signal indicative of the operation amount (the amount of depression) of the pedal  28   a  from the reference position. 
     The controller  30  controls operation of the electric motor  14  such that the drum  12  rotates according to operation of the lever  26   a , as well as controlling braking operation of the drum  12  by the braking device  24  according to operation of the pedal  28   a . Specifically, the controller  30  controls the inverter  20  in response to information, input from the operation lever device  26 , indicating an operation direction and an operation amount of the lever  26   a , thereby causing the inverter  20  to supply, to the electric motor  14 , a current allowing the electric motor  14  to cause the drum  12  to rotate according to the information input from the operation lever device  26 . Additionally, the controller  30  controls braking operation of the braking device  24  in response to a signal input from the brake pedal device  28 . Detailed internal configuration of the controller  30  will be described later. 
     The load meter  32  detects a load on the drum  12  via the hoisting rope  4 . Specifically, the load meter  32  detects a tension of the hoisting rope  4 . The load meter  32  successively detects a tension of the hoisting rope  4  and successively outputs the data item about the detected tension to the controller  30 . 
     The drum rotation meter  36  is for detecting an amount of rotation and a rotation speed of the drum  12 . For example, the drum rotation meter  36  includes a plurality of protrusions attached to one end surface of the drum  12  in a rotation shaft direction, and a proximity sensor arranged at the outside of the end surface of the drum  12  and the protrusions in the rotation shaft direction. The plurality of protrusions are arranged, on the end surface of the drum  12  to which the protrusions are attached, at equal intervals along a circumference of the drum  12  centered around the rotation shaft. The proximity sensor detects every passing of each protrusion through a position proximate to the proximity sensor as the drum  12  rotates, and outputs a pulse signal (detection signal) to the controller  30 . The controller  30  is configured to estimate an amount of rotation and a rotation speed of the drum  12  on the basis of an input pulse signal. 
     The setting unit  38  is for setting an allowable stopping height h which is a height of a lowest position at which the object  102  is required to be stopped at the time of the free-fall of the object  102 . The setting unit  38  is, for example, an input device for inputting a value of the allowable stopping height h. A height about the object  102  represents a height from a landing point below the object  102  to a lower end of the object  102 . The value of the allowable stopping height h set (input) by the setting unit  38  is sent from the setting unit  38  to the controller  30 . 
     Next, the internal configuration of the controller  30  will be described. 
     As shown in  FIG. 2 , the controller  30  has a storage section  40  and also has a data acquisition section  41 , an operational braking force estimation section  42 , a required braking force estimation section  44 , a regenerative capacity calculation section  46 , a required capacity calculation section  48 , a braking force determination section  50  and a control section  52  which serve as a functional block. 
     The storage section  40  stores various kinds of data items. Specifically, the storage section  40  stores operation amount-braking force characteristics which is a correlation between an operation amount of the pedal  28   a  and a braking force to be applied to the drum  12  according to the operation amount. The operation amount-braking force characteristics in the present embodiment, as shown in  FIG. 3 , exhibit a correlation in which the braking force is maintained at 0 from the point of the operation amount 0 corresponding to the reference position of the pedal  28   a  to a predetermined point A at which the operation amount of the pedal  28   a  slightly increases, and the braking force linearly increases from the predetermined point A as the operation amount of the pedal  28   a  increases. A range of the operation amount of the pedal  28   a  from 0 to the predetermined point A is a range corresponding to a play of the pedal  28   a  and corresponding to a dead region in which no braking force is applied to the drum  12  even when the pedal  28   a  is operated. Additionally, the storage section  40  stores a value of the allowable stopping height h to be sent from the setting unit  38  to the controller  30 . 
     The data acquisition section  41  acquires various kinds of data items related to operation of the crane during hoisting work. For example, the data acquisition section  41  acquires data items about a falling speed of the object  102  at the time of the free-fall of the object  102 , a mass of the object  102 , a height of the position of the object  102 , the operation amount of the pedal  28   a , and the like. 
     The data acquisition section  41  acquires a falling speed of the object  102  on the basis of the pulse signal input from the proximity sensor of the drum rotation meter  36  to the controller  30 , a draw-out amount (take-up amount) of the hoisting rope  4  per one rotation of the drum  12 , and the number of windings of the hoisting rope  4  around the hook sheave and the top sheave  3 . Specifically, the data acquisition section  41  counts the number of the pulse signals input from the proximity sensor of the drum rotation meter  36  to the controller  30  per unit time. This number of pulse signals per unit time is proportional to the amount of rotation of the drum  12  per unit time (the rotation speed of the drum  12 ). The data acquisition section  41  calculates the amount of rotation of the drum  12  per unit time from the counted number of pulse signals per unit time on the basis of the proportional relation. Then, the data acquisition section  41  calculates the falling speed of the object  102  by dividing, by the number of windings of the hoisting rope  4 , a value obtained by multiplying the calculated amount of rotation of the drum  12  per unit time by the draw-out amount of the hoisting rope  4  per one rotation of the drum  12 . 
     Additionally, the data acquisition section  41  acquires a mass of the object  102  from data item about a tension of the hoisting rope  4  input from the load meter  32  to the controller  30 . 
     Additionally, the data acquisition section  41  calculates the amount of rotation of the drum  12  corresponding to the counted number of pulse signals on the basis of the proportional relation between the number of pulse signals input to the controller  30  from the proximity sensor of the drum rotation meter  36  and the amount of rotation of the drum  12 . Additionally, the data acquisition section  41  acquires information indicating whether the calculated amount of rotation of the drum  12  is the amount of rotation for the raising direction or the lowering direction as the rotation direction, on the basis of information indicative of the operation direction of the lever  26   a  input from the operation lever device  26  to the controller  30 . Then, the data acquisition section  41  successively calculates an amount of change in position of the height of the object  102  in the raising direction or the lowering direction on the basis of the amount of rotation of the drum  12  associated with the acquired rotation direction of the drum  12 , the draw-out amount of the hoisting rope  4  per one rotation of the drum  12 , and the number of windings of the hoisting rope  4 . Specifically, the data acquisition section  41  calculates an amount of change in position of the height of the object  102  by dividing, by the number of windings of the hoisting rope  4 , a value obtained by multiplying the calculated amount of rotation of the drum  12  by the draw-out amount of the hoisting rope  4  per one rotation of the drum  12 . The data acquisition section  41  successively calculates the amount of change in position of the height of the object  102  from a time point when the object  102  lands at the landing point and adds the records of the calculated amount of change, thereby acquiring a current height of the object  102  from the landing point. 
     Additionally, from a signal input from the brake pedal operation device  28  to the controller  30 , the data acquisition section  41  acquires the operation amount of the pedal  28   a  which is indicated by the signal. 
     The operational braking force estimation section  42  (see  FIG. 2 ) estimates an operational braking force which is a braking force according to the operation amount from the reference position of the pedal  28   a . Specifically, the operational braking force estimation section  42  estimates, on the basis of the operation amount-braking force characteristics stored in the storage section  40 , an operational braking force corresponding to the operation amount of the pedal  28   a  acquired by the data acquisition section  41 . In other words, the operational braking force estimation section  42  estimates an operational braking force corresponding to the operation amount of the pedal  28   a  indicated by the signal input from the brake pedal device  28  to the controller  30 . 
     The required braking force estimation section  44  (see  FIG. 2 ) estimates a required braking force which is a braking force required to be applied to the drum  12  in order to stop the free-falling object  102  (see  FIG. 1 ) at a position corresponding to the allowable stopping height h. 
     The regenerative capacity calculation section  46  (see  FIG. 2 ) calculates a regenerative capacity which is an energy capacity corresponding to electric power that can be consumed by the regenerative power consumption unit  22  (see  FIG. 1 ). 
     The required capacity calculation section  48  (see  FIG. 2 ) calculates a required capacity which is an energy capacity of the regenerative power consumption unit  22  (see  FIG. 1 ), the required capacity being required for the regenerative braking to bear a remaining braking force obtained by subtracting the required braking force from the operational braking force. 
     The braking force determination section  50  determines each of a first braking force to be borne by the braking device  24  and a second braking force to be borne by the regenerative braking out of the operational braking force estimated by the operational braking force estimation section  42 . 
     Specifically, at the time of stopping the free-falling object  102 , when the operational braking force estimated by the operational braking force estimation section  42  is equal to or greater than the required braking force estimated by the required braking force estimation section  44 , the braking force determination section  50  determines a braking force equal to or greater than the required braking force as the first braking force and a remaining braking force obtained by subtracting the first braking force from the operational braking force as the second braking force. 
     More specifically, at the time of stopping the free-falling object  102 , when the operational braking force estimated by the operational braking force estimation section  42  is equal to the required braking force estimated by the required braking force estimation section  44 , the braking force determination section  50  determines an operational braking force equal to the required braking force as the first braking force. In this case, since the remaining braking force obtained by subtracting the first braking force from the operational braking force attains 0, the second braking force is determined to be 0. 
     Additionally, at the time of stopping the free-falling object  102 , when the operational braking force estimated by the operational braking force estimation section  42  is greater than the required braking force estimated by the required braking force estimation section  44 , the braking force determination section  50  determines each of the first braking force and the second braking force according to a large/small relation between the regenerative capacity calculated by the regenerative capacity calculation section  46  and the required capacity calculated by the required capacity calculation section  48 . Specifically, in this case, when the regenerative capacity calculated by the regenerative capacity calculation section  46  is equal to or greater than the required capacity calculated by the required capacity calculation section  48 , the braking force determination section  50  determines the required braking force estimated by the required braking force estimation section  44  as the first braking force, and a remaining braking force obtained by subtracting the required braking force from the operational braking force estimated by the operational braking force estimation section  42  as the second braking force. Additionally, when the regenerative capacity calculated by the regenerative capacity calculation section  46  is smaller than the required capacity calculated by the required capacity calculation section  48 , the braking force determination section  50  calculates the regenerative braking force generated in the electric motor  14  when the regenerative power corresponding to the regenerative capacity is consumed. Then, the braking force determination section  50  determines a remaining braking force obtained by subtracting the calculated regenerative braking force from the operational braking force estimated by the operational braking force estimation section  42  as the first braking force, as well as determining the calculated regenerative braking force as the second braking force. 
     Additionally, when, at the time of stopping the free-falling object  102 , the operational braking force estimated by the operational braking force estimation section  42  is smaller than the required braking force estimated by the required braking force estimation section  44 , the braking force determination section  50  determines the operational braking force estimated by the operational braking force estimation section  42  as the first braking force. In this case, since the remaining braking force obtained by subtracting the first braking force from the operational braking force attains 0, the second braking force is determined to be 0. 
     The control section  52  causes the braking device  24  to apply the first braking force determined by the braking force determination section  50  to the drum  12 . Specifically, the control section  52  controls braking operation of the braking device  42  such that the braking device  24  applies the first braking force determined by the braking force determination section  50  to the drum  12 . 
     Next, with reference to the flow chart of  FIG. 4 , operation of the electric winch device according to the present embodiment will be described. Specifically, description will be made of operation of the electric winch device to be conducted at the time of stopping the free-falling object  102 . The flow chart of  FIG. 4  shows a control process of one cycle for operation control of the electric winch device according to the present embodiment. 
     First, before the free-fall of the object  102 , the value of the allowable stopping height h is set by the setting unit  38  in advance. The allowable stopping height h is set, for example, to be a value larger than a height of a vehicle or a worker which might enter below the object  102 . The allowable stopping height h set by the setting unit  38  is stored in the storage section  40  of the controller  30 . 
     Then, the free-fall of the object  102  is conducted and the operator depresses the pedal  28   a  of the brake pedal device  28  from the reference position at predetermined timing for stopping the moving-down of the object  102 . Responsively, a signal indicative of the operation amount (an amount of depression) from the reference position of the pedal  28   a  is input from the brake pedal device  28  to the controller  30 . 
     Thereafter, the data acquisition section  41  of the controller  30  acquires various kinds of data items. Here, in response to input of the signal from the brake pedal device  28  to the controller  30 , the data acquisition section  41  acquires a falling speed of the object  102  at that time point, the mass of the object  102 , a height of the object  102  from the landing point at that time point, and an operation amount of the pedal  28   a  (Step S 1 ). Specifically, on the basis of the pulse signal input from the proximity sensor of the drum rotation meter  36 , the data acquisition section  41  acquires the falling speed of the object  102  and the height of the object  102  from the landing point by the above-described method. Additionally, the data acquisition section  41  acquires a mass of the object  102  from the data item about the tension of the hoisting rope  4  input from the load meter  32  to the controller  30 . Additionally, the data acquisition section  41  acquires the operation amount (the amount of depression) of the pedal  28   a  from the signal input from the brake pedal device  28  to the controller  30 . Each of the acquired data items is stored in the storage section  40 . 
     Next, the operational braking force estimation section  42  of the controller  30  estimates an operational braking force F according to the operation amount from the reference position of the pedal  28   a  (Step S 2 ). Specifically, the operational braking force estimation section  42  estimates, as the operational braking force F, a braking force corresponding to the operation amount of the pedal  28   a  acquired at the Step S 1  on the basis of the operation amount-braking force characteristics (see  FIG. 3 ) stored in the storage section  40 . 
     Thereafter, the required braking force estimation section  44  of the controller  30  calculates a required braking force F h  required for stopping the currently free-falling object  102  at a position corresponding to the allowable stopping height h (Step S 3 ). Specifically, the required braking force estimation section  44  calculates the required braking force F h  on the basis of Equation (1) below. Here, v 0  represents a falling speed of the object  102  acquired at the Step S 1 , m represents a mass of the object  102  acquired at the Step S 1 , H represents a height from the landing point to the lower end of the object  102 , the height being acquired at the Step S 1 , and g represents a gravitational acceleration. The required braking force estimation section  44  calculates the required braking force F h  using these values and the value of the allowable stopping height h stored in the storage section  40 . 
     
       
         
           
             
               
                 
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     Next, the braking force determination section  50  of the controller  30  compares the required braking force F h  calculated by the required braking force estimation section  44  with the operational braking force F estimated by the operational braking force estimation section  42  at the Step S 2  to determine a large/small relation between the required braking force F h  and the operational braking force F (Step S 4 ). 
     When determining that the operational braking force F is smaller than the required braking force F h , the braking force determination section  50  determines the operational braking force F as the first braking force to be borne by the braking device  24 , as well as determining the second braking force to be borne by the regenerative braking to be 0 (Step S 5 ). This case corresponds to a case where the operator stops the object  102  at a position at a height lower than the allowable stopping height h by intentionally adjusting the operation amount of the pedal  28   a  such that the operational braking force F is smaller than the required braking force F h . 
     Additionally, also when determining that the operational braking force F is equal to the required braking force F h , the braking force determination section  50  determines the operational braking force F as the first braking force to be borne by the braking device  24 , as well as determining the second braking force to be borne by the regenerative braking to be 0 (Step S 6 ). 
     Additionally, when the braking force determination section  50  determines that the operational braking force F is greater than the required braking force F h , next the regenerative capacity calculation section  46  calculates a regenerative capacity E c  which is electric power that can be consumed by the regenerative power consumption unit  22  at this time point (Step S 7 ). Specifically, when the regenerative power consumption unit  22  includes only a storage battery as in the present embodiment, the regenerative capacity calculation section  46  senses a charge condition of the storage battery to calculate a remaining capacity that can be charged in the storage battery as the regenerative capacity E c . Additionally, when the regenerative power consumption unit  22  includes a combination of a storage battery and a regenerative resistor, the regenerative capacity calculation section  46  calculates the regenerative capacity E c  by adding the remaining capacity of the storage battery and the electric power that can be consumed by the regenerative resistor. 
     Thereafter, the required capacity calculation section  48  calculates a required capacity E b  required for the regenerative braking to bear a remaining braking force obtained by subtracting the required braking force F h  from the operational braking force F (Step S 8 ). Specifically, the required capacity calculation section  48  first calculates a braking force (F−F h ) of a difference between the operational braking force F and the required braking force F h , as well as calculating, on the basis of Equation (2) below, the required capacity E b  which is required by the regenerative power consumption unit  22  to obtain the calculated braking force (F−F h ) by the regenerative braking. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       E 
                       b 
                     
                     = 
                     
                       
                         ( 
                         
                           F 
                           - 
                           
                             F 
                             h 
                           
                         
                         ) 
                       
                       × 
                       
                         
                           mv 
                           0 
                           2 
                         
                         
                           2 
                           ⁢ 
                           
                             ( 
                             
                               F 
                               - 
                               
                                 m 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 g 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Next, the braking force determination section  50  determines a large/small relation between the regenerative capacity E c  calculated at the Step S 7  and the required capacity E b  calculated at the Step S 8  (Step S 9 ). 
     When determining that the regenerative capacity E c  is equal to or greater than the required capacity E b , the braking force determination section  50  determines the required braking force F h  estimated by the required braking force estimation section  44  at the Step S 3  to be the first braking force to be borne by the braking device  24 , as well as determining the differential braking force (F−F h ) to be the second braking force to be borne by the regenerative braking (Step S 10 ). The case where the regenerative capacity E c  is equal to or greater than the required capacity E b  corresponds to a case where the regenerative power consumption unit  22  has a capacity that enables the differential braking force (F−F h ) to be borne by the regenerative braking. 
     On the other hand, when determining that the regenerative capacity E c  is smaller than the required capacity E b , the braking force determination section  50  calculates a braking force F r  (regenerative braking force F r ) generated in the electric motor  14  due to consumption of the regenerative power corresponding to the regenerative capacity E c  (Step S 11 ). Specifically, the braking force determination section  50  calculates the regenerative braking force F r  satisfying the Equation (3) below. The case where the regenerative capacity E c  is smaller than the required capacity E b  corresponds to a case where the energy capacity (the amount of electric power that can be consumed) of the regenerative power consumption unit  22  is insufficient for the regenerative braking to bear the differential braking force (F−F h ). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       E 
                       c 
                     
                     = 
                     
                       
                         F 
                         r 
                       
                       × 
                       
                         
                           mv 
                           0 
                           2 
                         
                         
                           2 
                           ⁢ 
                           
                             ( 
                             
                               F 
                               - 
                               
                                 m 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 g 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Then, the braking force determination section  50  determines a remaining braking force (F−F r ) obtained by subtracting the calculated regenerative braking force F r  from the operational braking force F as the first braking force to be borne by the braking device  24 , as well as determining the calculated regenerative braking force F r  as the second braking force to be borne by the regenerative braking (Step S 12 ). The braking force (F−F r ) has a value greater than the required braking force F h . 
     Lastly, the control section  52  controls braking operation of the braking device  24  such that the braking device  24  applies the first braking force determined by the braking force determination section  50  to the drum  12  (Step S 13 ). Responsively, the first braking force determined at the Step S 5 , S 6 , S 10  or S 12  is applied to the drum  12  by the braking device  24 . Additionally, after the Step S 10  or S 12 , the second braking force determined at these Steps is generated in the electric motor  14  due to consumption of the regenerative power by the regenerative power consumption unit  22 . As a result, the operational braking force F according to the operation amount of the pedal  28   a  is applied to the drum  12 . 
     Thereafter, the processing at and after the Step S 1  is repeated. As a result, when the operation amount of the pedal  28   a  changes, the operational braking force F according to the changed operation amount is applied to the drum  12 . 
     In the foregoing manner, the operational braking force is applied to the drum  12  according to the operation of the pedal  28   a  by the operator, resulting in stopping the free-fall of the object  102 . 
     As described in the foregoing, in the electric winch device according to the present embodiment, at the time of stopping the free-falling object  102 , when the operational braking force F is equal to or greater than the required braking force F h , the braking device  24  applies the first braking force equal to or greater than the required braking force F h  to the drum  12 . Therefore, even when, at the operation of the pedal  28   a  for stopping the free-falling object  102 , because of a fail developing in an electric system leading from the regenerative power consumption unit  22  to the electric motor  14 , no braking force is obtained by regenerative braking to result in failing to obtain the second braking force to be borne by the regenerative braking out of the operational braking force according to the operation amount of the pedal  28   a , applying the first braking force equal to or greater than the required braking force F h  by the braking device  24  to the drum  12  enables the object  102  to be stopped at a position at a height equal to or larger than the allowable stopping height h. Accordingly, even when a fail develops in the electric system leading from the regenerative power consumption unit  22  to the electric motor  14 , the electric winch device according to the present embodiment prevents the object  102 , at the time of the free-fall of the object  102 , from moving down to a position at a height lower than the allowable stopping height h. 
     Additionally, in the electric winch device according to the present embodiment, in a case where the operational braking force F is greater than the required braking force F h  at the time of stopping the free-falling object  102 , when the regenerative capacity E c  of the regenerative power consumption unit  22  is smaller than the required capacity E b , the braking force determination section  50  calculates the regenerative braking force F r  generated in the electric motor  14  at the consumption of the regenerative power corresponding to the required capacity E b , and the braking device  24  applies the remaining braking force (F−F r ) obtained by subtracting the calculated regenerative braking force F r  from the operational braking force F to the drum  12 . Accordingly, at the time of stopping the free-falling object  102 , even when the regenerative capacity E c  of the regenerative power consumption unit  22  is short, the electric winch device according to the present embodiment enables the braking device  24  to bear a braking force corresponding to the short of the capacity. Thus, even when the regenerative capacity E c  of the regenerative power consumption unit  22  is short at the time of stopping the free-falling object  102 , the operational braking force F according to the operation amount of the pedal  28   a  can be applied to the drum  12  to stop the object  102 . 
     Additionally, at the time of stopping the free-falling object  102 , when the operational braking force F is smaller than the required braking force F h , the electric winch device according to the present embodiment causes the braking device  24  to apply the braking force equal to the operational braking force F to the drum  12 . Accordingly, also in this case, the operational braking force F according to the operation amount of the pedal  28   a  by the operator can be applied to the drum  12  to stop the object  102 . 
     The embodiment disclosed here is for illustrative purpose only and it is not to be construed as limiting in any manner. The scope of the present invention is shown not by the description of the embodiment but by the scope of claims and further includes meanings equivalent to the scope of claims and all the modification within the scope. 
     For example, an object to be raised/lowered is not limited to such an integral combination of the hook device and the hoisting load as described above. For example, a bucket such as a clamshell may be an object. Then, the present invention may be applicable to an electric winch device of a crane that conducts digging work by causing the bucket to free fall, for example. 
     Outline of Embodiment 
     The embodiment is summarized as follows. 
     The electric winch device according to the embodiment is an electric winch device provided in a crane for raising and lowering an object, the electric winch device comprising: an electric motor; a winch drum driven by the electric motor to rotate for raising of the object; a braking device which brakes rotation of the winch drum; a braking operation part to be operated for stopping moving-down of the object; a regenerative power consumption unit which consumes at least a part of regenerative power regenerated by the electric motor at the moving-down of the object to cause the electric motor to generate a braking force on the rotation of the winch drum; a setting unit for setting an allowable stopping height which is a height of a lowest position at which the object is required to be stopped at a time of a free-fall of the object; an operational braking force estimation section which estimates an operational braking force which is a braking force according to an operation amount of the braking operation part; a required braking force estimation section which estimates a required braking force which is a braking force required to stop the free-falling object at a position at the allowable stopping height set by the setting unit; a braking force determination section which determines, out of the operational braking force, each of a first braking force to be borne by the braking device and a second braking force to be borne by a braking force which is generated in the electric motor due to consumption of the regenerative power; and a control section which causes the braking device to apply the first braking force, which has been determined by the braking force determination section, to the winch drum. The braking force determination section determines the first braking force to be a braking force equal to or greater than the required braking force when, at a time of stopping of the free-falling object, the operational braking force estimated by the operational braking force estimation section is equal to or greater than the required braking force estimated by the required braking force estimation section. 
     In this electric winch device, even in a case where, at the operation of the braking operation part for stopping the free-falling object, no braking force is obtained by regenerative braking due to a fail developing in an electric system leading from the regenerative power consumption unit to the electric motor, resulting in failing to obtain the second braking force to be borne by the regenerative braking out of the operational braking force according to the operation amount of the braking operation part, when the operational braking force estimated by the operational braking force estimation section is equal to or greater than the required braking force estimated by the required braking force estimation section, the braking device applies the first braking force equal to or greater than the required braking force to the winch drum. Therefore, the object can be stopped at a position at a height equal to or larger than the allowable stopping height. Accordingly, even when a fail develops in the electric system leading from the regenerative power consumption unit to the electric motor, the present electric winch device prevents the object, at the time of the free-fall thereof, from moving down to a position at a height lower than the allowable stopping height. 
     It is preferable that the electric winch device further includes a regenerative capacity calculation section which calculates a regenerative capacity corresponding to electric power which can be consumed by the regenerative power consumption unit; and a required capacity calculation section which calculates a required capacity which is an energy capacity of the regenerative power consumption unit, the required capacity being an energy capacity required for the electric motor to generate a remaining braking force obtained by subtracting the required braking force from the operational braking force, wherein in a case where the operational braking force is greater than the required braking force at the time of stopping the free-falling object, when the regenerative capacity calculated by the regenerative capacity calculation section is equal to or greater than the required capacity calculated by the required capacity calculation section, the braking force determination section determines the first braking force to be a braking force equal to the required braking force, and when the regenerative capacity calculated by the regenerative capacity calculation section is smaller than the required capacity calculated by the required capacity calculation section, the braking force determination section calculates a regenerative braking force which is a braking force generated in the electric motor due to consumption of the regenerative power corresponding to the regenerative capacity and determines a remaining braking force obtained by subtracting the calculated regenerative braking force from the operational braking force as the first braking force. 
     According to this configuration, at the time of stopping the free-falling object, even when a regenerative capacity of the regenerative power consumption unit falls short of a required capacity which is required for the electric motor to generate a remaining braking force obtained by subtracting a required braking force from an operational braking force, a braking force corresponding to the capacity shortage can be borne by the braking device. Therefore, even when the regenerative power consumption unit is short of a regenerative capacity at the time of stopping the free-falling object, it is possible to apply an operational braking force according to the operation amount of the braking operation part to the winch drum to thereby stop the object. 
     In this case, the braking force determination section may calculate the regenerative braking force on the basis of the operational braking force estimated by the operational braking force estimation section, the regenerative capacity calculated by the regenerative capacity calculation section, a mass of the object at a time point when operation of the braking operation part starts, a falling speed of the object at a time point when operation of the braking operation part starts, a height from a landing point below the object to the object at a time point when operation of the braking operation part starts, and the allowable stopping height set by the setting unit. 
     In the electric winch device, it is preferable that when the operational braking force estimated by the operational braking force estimation section at the time of stopping the free-falling object is smaller than the required braking force estimated by the required braking force estimation section, the braking force determination section determines the first braking force to be a braking force equal to the operational braking force. 
     According to this configuration, when an operational braking force is smaller than a required braking force at the time of stopping the free-falling object, it is possible to apply an operational braking force according to an operation amount of the braking operation part to the winch drum to thereby stop the object. 
     As described in the foregoing, according to the embodiment, it is possible to prevent an object, at the time of the free-fall of the object, from moving down to a position at a height lower than an allowable stopping height even when a fail develops in an electric system leading from the regenerative power consumption unit to the electric motor, in the electric winch device of the crane provided with a regeneration function.