Vibrating screed

Abstract

A vibrating screed including a screed member, a brushless direct-current motor, a power switching network coupled between a power source and the brushless direct-current motor, and an exciter assembly that vibrates the screed member when torque is received from the motor, and an electric processor. The electric processor is electrically coupled to the motor and the power switching network and is configured to operate the brushless direct-current motor at a selected speed by providing pulse-width modulated signals to the power switching network, the pulse-width modulated signals having a duty ratio, determine a current speed of the brushless direct-current motor, determine whether a difference between the selected speed and the current speed is above a threshold amount, and modify the duty ratio by a predetermined amount when the difference between the selected speed and the current speed is above the threshold amount to continue operating the motor at the selected speed.

What is claimed is: 
     
         1 . A vibrating screed comprising:
 a screed member;   a brushless direct-current motor;   a power switching network coupled between a power source and the brushless direct-current motor;   an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft, the exciter assembly comprising
 a first eccentric mass fixed on the driveshaft, and 
 a second eccentric mass axially moveable along the driveshaft between a first position and a second position in which the second eccentric mass is closer to the first eccentric mass than in the first position; and 
   an electronic processor electrically coupled to the motor and the power switching network and configured to
 operate the brushless direct-current motor at a selected speed by providing pulse-width modulated signals to the power switching network, the pulse-width modulated signals having a duty ratio, 
 determine a current speed of the brushless direct-current motor, 
 determine whether a difference between the selected speed and the current speed is above a threshold amount, and 
 modify the duty ratio by a predetermined amount when the difference between the selected speed and the current speed is above the threshold amount to continue operating the motor at the selected speed. 
   
     
     
         2 . The vibrating screed of  claim 1 , wherein the electronic processor is further configured to
 increase the duty ratio by the predetermined amount when the current speed is below the selected speed by greater than the threshold amount.   
     
     
         3 . The vibrating screed of  claim 1 , wherein the electronic processor is further configured to
 decrease the duty ratio by the predetermined amount when the current speed is above the selected speed by greater than the threshold amount.   
     
     
         4 . The vibrating screed of  claim 1 , further comprising a rotor position sensor configured to detect a rotor position of the brushless direct-current motor, wherein the electronic processor is electrically coupled to the rotor position sensor and further configured to
 receive, from the rotor position sensor, signals indicating the rotor position, and   determine the current speed of the motor based on the signals indicating the rotor position.   
     
     
         5 . The vibrating screed of  claim 1 , wherein the electronic processor is further configured to
 determine the current speed of the motor based on back electro-motive force generated in one or more inactive phases of the brushless direct-current motor.   
     
     
         6 . The vibrating screed of  claim 1 , further comprising a mode selection member to switch the exciter assembly between a first low vibration mode and a second high vibration mode, wherein the electronic processor is electrically coupled to the mode selection member to receive selection signals, the electronic processor further configured to
 set the selected speed to a first speed when the first low vibration mode is selected using the mode selection member, and   set the selected speed to a second speed when the second high vibration mode is selected using the mode selection member.   
     
     
         7 . The vibrating screed of  claim 6 , wherein the first speed is at greater than 9,000 rotations per minute and the second speed is less than 15,000 rotations per minute. 
     
     
         8 . The vibrating screed of  claim 1 , further comprising a frame coupled to the screed member via a first plurality of vibration dampers configured to attenuate a transfer of vibration from the screed member to the frame. 
     
     
         9 . The vibrating screed of  claim 8 , further comprising a housing in which the electronic processor is located, the housing coupled to the frame via a second plurality of vibration dampers configured to attenuate a transfer of vibration from the frame to the housing. 
     
     
         10 . A vibrating screed comprising:
 a screed member;   a brushless direct-current motor including a rotor and a stator;   a power switching network coupled between a power source and the brushless direct-current motor;   an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft, the exciter assembly comprising
 a first eccentric mass fixed on the driveshaft, and 
 a second eccentric mass axially moveable along the driveshaft between a first position and a second position in which the second eccentric mass is closer to the first eccentric mass than in the first position; and 
   an electronic processor electrically coupled to the motor and the power switching network and configured to
 operate the brushless direct-current motor at a selected speed by providing pulse-width modulated signals to the power switching network, the pulse-width modulated signals having a duty ratio, and 
 modify the duty ratio to cause the motor to operate at the selected speed when it is detected that the brushless direct-current motor is operating at a current speed that is different from the selected speed. 
   
     
     
         11 . The vibrating screed of  claim 10 , wherein the electronic processor is further configured to
 increase the duty ratio when the current speed is below the selected speed by greater than a threshold amount; and   decrease the duty ratio when the current speed is above the selected speed by greater than the threshold amount.   
     
     
         12 . The vibrating screed of  claim 10 , further comprising a rotor position sensor configured to detect a rotor position of the brushless direct-current motor, wherein the electronic processor is electrically coupled to the rotor position sensor and further configured to
 receive, from the rotor position sensor, signals indicating the rotor position, and   determine the current speed of the motor based on the signals indicating the rotor position.   
     
     
         13 . The vibrating screed of  claim 10 , wherein the electronic processor is further configured to
 determine the current speed of the motor based on back electro-motive force generated in one or more inactive phases of the brushless direct-current motor.   
     
     
         14 . The vibrating screed of  claim 10 , further comprising:
 a frame coupled to the screed member via a first plurality of vibration dampers configured to attenuate a transfer of vibration from the screed member to the frame; and   a housing in which the electronic processor is located, the housing coupled to the frame via a second plurality of vibration dampers configured to attenuate a transfer of vibration from the frame to the housing.   
     
     
         15 . A vibrating screed comprising:
 a screed member;   a brushless direct-current motor including a rotor and a stator;   a power switching network coupled between a battery pack and the brushless direct-current motor;   an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft, the exciter assembly comprising
 a first eccentric mass fixed on the driveshaft, and 
 a second eccentric mass axially moveable along the driveshaft between a first position and a second position in which the second eccentric mass is closer to the first eccentric mass than in the first position; and 
   an electronic processor electrically coupled to the motor and the power switching network and configured to operate and maintain the brushless direct-current motor at a selected speed independent of a state of charge of the battery pack.   
     
     
         16 . The vibrating screed of  claim 15 , wherein the electronic processor is further configured to
 increase a duty ratio of pulse-width modulated signals provided to the power switching network when a current speed is below the selected speed by greater than a threshold amount.   
     
     
         17 . The vibrating screed of  claim 16 , wherein the electronic processor is further configured to
 decrease the duty ratio of pulse-width modulated signals provided to the power switching network when the current speed is above the selected speed by greater than the threshold amount.   
     
     
         18 . The vibrating screed of  claim 17 , further comprising a rotor position sensor configured to detect a rotor position of the brushless direct-current motor, wherein the electronic processor is electrically coupled to the rotor position sensor and further configured to
 receive, from the rotor position sensor, signals indicating the rotor position, and   determine the current speed of the motor based on the signals indicating the rotor position.   
     
     
         19 . The vibrating screed of  claim 17 , wherein the electronic processor is further configured to
 determine the current speed of the motor based on back electro-motive force generated in one or more inactive phases of the brushless direct-current motor.   
     
     
         20 . The vibrating screed of  claim 15 , further comprising
 a frame coupled to the screed member via a first plurality of vibration dampers configured to attenuate a transfer of vibration from the screed member to the frame, and   a housing in which the electronic processor is located, the housing coupled to the frame via a second plurality of vibration dampers configured to attenuate a transfer of vibration from the frame to the housing.