Construction machine

Abstract

A construction machine includes: a swing structure ( 1 d ); an electric motor ( 16 ) that drives the swing structure; an operating device ( 4 b ) that outputs an operating signal according to an operating amount and an operating direction; an inverter device ( 13 ) that controls the electric motor based on a control signal generated based on the operating signal; a position sensor ( 24 ) that detects an actual speed of the electric motor; and a second controller ( 22 ) that determines whether at least one of a first condition and a second condition is satisfied. The first condition is satisfied when a sign of a value computed by subtracting the actual speed V from a target speed V* of the electric motor that defined by the control signal; and the second condition is satisfied when a difference between the target speed and the actual speed is greater than a reference value Vth, and when the acceleration is greater than a reference value βth. This prevents erroneous determination and failure of detection relating to determination of faults in an electronic control system from occurring.

1 . A construction machine comprising:
 a swing structure;   an electric motor that drives the swing structure;   an operating device that outputs an operating signal for operating the electric motor according to an operating amount and an operating direction;   first control means that controls the electric motor based on a control signal generated based on the operating signal;   detecting means that detects an actual speed of the electric motor; and   second control means that determines whether at least one of a first condition and a second condition is satisfied, the first condition that is satisfied when a sign of a value computed by subtracting the actual speed from a target speed of the electric motor, the target speed defined by the control signal, is different from a sign of acceleration of the electric motor, and the second condition that is satisfied when a difference value between the target speed and the actual speed is greater than a first reference value and when the acceleration is greater than a second reference value.   
     
     
         2 . The construction machine according to  claim 1 , further comprising:
 a braking device that brakes the electric motor based on a braking signal, wherein   the second control means outputs the braking signal to the braking device when at least one of the first condition and the second condition is satisfied.   
     
     
         3 . The construction machine according to  claim 1 , further comprising:
 an annunciating device that annunciates occurrence of a fault in the construction machine based on an annunciation signal, wherein   the second control means outputs the annunciation signal to the annunciating device when at least one of the first condition and the second condition is satisfied.   
     
     
         4 . The construction machine according to  claim 1 , further comprising:
 acceleration detecting means that detects acceleration of the electric motor.   
     
     
         5 . The construction machine according to  claim 1 , wherein the acceleration of the electric motor is calculated based on target torque of the electric motor defined by the control signal or actual torque generated by the electric motor. 
     
     
         6 . The construction machine according to  claim 1 , wherein the first control means differs from the second control means.