Electric treadmill

Abstract

An electric treadmill includes an endless belt, a motor and a motor driving circuit. The motor driving circuit is operable to control electric current flow from a positive electrode through the motor to a negative electrode to drive the motor. The motor driving circuit has a power resistor and a switch element connected in series between the positive electrode and the negative electrode. When the motor driving circuit receives power from an external power source, the switch element automatically switches to an open state so that the power resistor is inactive. When the motor driving circuit does not receive power from the external power source, the switch element automatically switches to a closed state, and the power resistor becomes a load for consuming power generated by the motor when the endless belt is driven by an external force, such that the motor operates to resist rotation of the endless belt.

1 . An electrical treadmill, comprising:
 a frame;   an endless belt movable relative to the frame;   a motor coupled to the endless belt; and   a motor driving circuit connected to the motor, having a positive electrode, a negative electrode and a switch element connected between the positive electrode and the negative electrode, the motor driving circuit configured to control electric current from the positive electrode through the motor to the negative electrode to drive the motor; and   a power resistor connected to the switch element in series between the positive electrode and the negative electrode;   wherein when the motor driving circuit receives power from an external power source, the switch element automatically switches to an open state so that the power resistor is inactive and the motor is operable to drive the endless belt to rotate; and   wherein when the motor driving circuit does not receive power from the external power source, the switch element automatically switches to a closed state, and the power resistor becomes a load for consuming power generated by the motor when the endless belt is driven by an external force, such that the motor operates to resist rotation of the endless belt and ensure a sliding speed of the endless belt will not exceed 1 mph.   
     
     
         2 . The electric treadmill as claimed in  claim 1 , wherein the motor is an AC electric motor, the motor driving circuit comprising a rectifier configured to convert alternating current from the external power source to direct current, and an inverter configured to convert the direct current to alternating current flowing through the motor. 
     
     
         3 . The electric treadmill as claimed in  claim 2 , wherein the motor is a permanent-magnet synchronous motor having a three-phase winding and the inverter is a three-phase inverter. 
     
     
         4 . The electric treadmill as claimed in  claim 3 , wherein when the motor driving circuit does not receive power, the switch element switches to the closed state and rotation of the endless belt drives the motor to generated electric current through the power resistor, causing a high magnetic force applied to the motor to resist rotation of the endless belt. 
     
     
         5 . The electric treadmill as claimed in  claim 2 , wherein the rectifier has a pair of outputting terminals which constitute a DC bus of the motor driving circuit, including a positive terminal forming the positive electrode and a negative terminal forming the negative electrode. 
     
     
         6 . The electric treadmill as claimed in  claim 5 , wherein the motor driving circuit has a capacitor connected between the positive terminal and the negative terminal configured for filtration and stabilization to maintain an output voltage of the rectifier at a rated value. 
     
     
         7 . The electric treadmill as claimed in  claim 1 , wherein the motor driving circuit has an overvoltage protection circuit connected between the positive electrode and the negative electrode, configured to protect the motor driving circuit and the motor. 
     
     
         8 . The electric treadmill as claimed in  claim 1 , wherein the power resistor has a resistance value ranging from 10 to a value less than 50. 
     
     
         9 . The electric treadmill as claimed in  claim 5 , wherein the power resistor has a power value greater than 200 W. 
     
     
         10 . The electric treadmill as claimed in  claim 1 , further comprising an inclination adjusting mechanism configured for adjusting an angle of the platform relative to a ground, wherein when the motor driving circuit does not receive power, even if the platform of the electric treadmill is inclined at a maximum inclination angle and a user stands on the endless belt, a sliding speed of the endless belt will not exceed 1 mph. 
     
     
         11 . The electric treadmill as claimed in  claim 1 , further comprising an inclination adjusting mechanism configured for adjusting an angle of the platform relative to a ground, wherein when the motor driving circuit does not receive power, even if the platform of the electric treadmill is inclined at a grade of 20% and a user weighing up to 120 kg stands on the endless belt, a sliding speed of the endless belt will not exceed 1 mph. 
     
     
         12 . The electric treadmill as claimed in  claim 1 , further comprising a front roller mounted on a front end the frame and a rear roller mounted on a rear end of the frame, the endless belt mounted around the front roller and the rear roller and the motor coupled to the front roller or the rear roller for driving the endless belt to rotate with respect to the frame; wherein the endless belt is a slat belt comprising a plurality of elongated slats arranged parallel to each other and oriented perpendicular to an axis of rotation of the endless belt. 
     
     
         13 . An electrical treadmill, comprising:
 a frame;   an endless belt movable relative to the frame;   a motor coupled to the endless belt to drive the endless belt to rotate; and   a motor driving circuit connected to the motor, having a positive electrode and a negative electrode, the motor driving circuit configured to control electric current from the positive electrode through the motor to the negative electrode to drive the motor;   a first resistor connected between the positive electrode and the negative electrode, forming an overvoltage protection circuit; and   a second resistor and a switch element connected in series between the positive electrode and the negative electrode, the second resistor having a resistance value lower than the first resistor;   wherein when the motor driving circuit receives power form an external power source, the first resistor is active for overvoltage protection, and the switch element automatically switches to an open state so that the second resistor is inactive and the motor is operable to drive the endless belt to rotate; and   wherein when the motor driving circuit does not receive power from the external power source, the first resistor is inactive, and the switch element automatically switches to a closed state so that the second resistor is active and becomes a load for consuming power generated by the motor when the endless belt is driven by an external force, such that the motor operates to stop rotation of the endless belt.   
     
     
         14 . The electric treadmill as claimed in  claim 13 , wherein the motor is a permanent-magnet synchronous motor, the motor driving circuit comprising a rectifier configured to convert alternating current from the external power source to direct current, and an inverter configured to convert the direct current to alternating current flowing through the motor. 
     
     
         15 . The electric treadmill as claimed in  claim 14 , wherein when the motor driving circuit does not receive power, the switch element automatically switches to the closed state and rotation of the endless belt will drive the motor to generated electric current through the second resistor, causing a high magnetic force applied to the motor to resist rotation of the endless belt. 
     
     
         16 . The electric treadmill as claimed in  claim 13 , wherein the second resistor is a power resistor having a resistance value ranging from 10 to a value less than 50. 
     
     
         17 . The electric treadmill as claimed in  claim 16 , wherein the second resistor has a power value greater than 200 W. 
     
     
         18 . The electric treadmill as claimed in  claim 13 , wherein the overvoltage protection circuit includes the first resistor, a diode and a transistor, when the motor driving circuit detects that the voltage between the positive electrode and the negative electrode exceeds a rated value, the transistor is activated to protect the motor driving circuit. 
     
     
         19 . The electric treadmill as claimed in  claim 13 , further comprising an inclination adjusting mechanism configured for adjusting an angle of the platform relative to a ground, wherein when the motor driving circuit does not receive power, even if the platform of the electric treadmill is inclined at a maximum inclination angle and a user stands on the endless belt, a sliding speed of the endless belt will not exceed 1 mph. 
     
     
         20 . A method of stopping rotation of an endless belt of an electric treadmill when the electric treadmill does not receive power from an external power source, the method comprising:
 providing a motor coupled to the endless belt;   providing a motor driving circuit connected to the motor, the motor driving circuit including a positive electrode, a negative electrode and a switch element connected between the positive electrode and the negative electrode;   connecting a power resistor to the switch element in series between the positive electrode and the negative electrode of the motor driving circuit;   automatically switching the switch element to an open state when the motor driving circuit receives power from an external power source so that the power resistor is inactive and the motor is operable to drive end endless belt to rotate; and   automatically switching the switch element to a close state when the motor driving circuit does not receive power from the external power source so that the power resistor becomes a load for consuming power generated by the motor when the endless belt is driven by an external force, such that the motor operates to resist rotation of the endless belt and ensure a sliding speed of the endless belt will not exceed 1 mph.