Electronic braking for a power tool having a brushless motor
A power tool is provided including a housing, a brushless direct-current (BLDC) electric motor disposed inside the housing, power switches disposed between a power supply and the electric motor and including high-side switches and low-side switches, and a control unit configured to control a switching operation of the power switches to operate the electric motor and electronically brake the motor by simultaneously activating the high-side switches or the low-side switches to stop the rotation of the motor upon detection of a condition prompting the braking of the motor. The control unit is configured to detect the condition that prompts the braking of the electric motor, set a braking profile for braking the electric motor based on the detected condition, and execute braking of the electric motor using the braking profile.
1. A power tool comprising:
a housing;
a brushless direct-current (BLDC) electric motor disposed inside the housing, the electric motor including a rotor having one or more magnets and a stator including a plurality of windings;
a plurality of power switches disposed between a power supply and the electric motor, the plurality of power switches including a plurality of high-side switches and a plurality of low-side switches; and
a control unit configured to control a switching operation of the plurality of power switches to operate the electric motor and electronically brake the motor by simultaneously activating the plurality of the high-side switches or the plurality of low-side switches to apply a back-EMF (electro-magnetic force) current of the motor to the plurality of windings and thereby stop the rotation of the motor upon detection of a condition prompting the braking of the motor,
wherein the control unit is configured to: detect the condition that prompts the braking of the electric motor, set a braking profile for braking the electric motor based on the detected condition, and execute braking of the electric motor using the braking profile, and
wherein the braking profile is executed over a plurality of braking cycles of the same time-length and comprises a first braking segment during which a first braking force is applied to brake the motor by supplying a first amount of motor back-EMF current to the plurality of stator windings, followed by a second braking segment during which a second braking force different from the first braking force is applied to brake the motor by supplying a second amount of motor back-EMF current to the plurality of stator windings, wherein the first amount of motor back-EMF current per braking cycle is different from the second amount of back-EMF current per braking cycle.
2. The power tool of claim 1 , wherein the control unit executed hard braking to apply the first braking force to the motor during the first braking segment, and executes soft braking to apply the second braking force to the motor during the second braking segment, wherein the second braking force is less than the first braking force.
3. The power tool of claim 2 , wherein the control unit is configured to monitor a rotational speed of the motor and switch from the first braking segment to the second braking segment when the rotational speed of the motor falls below a predetermined threshold speed.
4. The power tool of claim 1 , wherein the control unit executed soft braking to apply the first braking force to the motor during the first braking segment, and executes hard braking to apply the second braking force to the motor during the second braking segment, wherein the first braking force is less than the second braking force.
5. A power tool comprising:
a housing;
a brushless direct-current (BLDC) electric motor disposed inside the housing, the electric motor including a rotor having one or more magnets and a stator including a plurality of windings;
a plurality of power switches disposed between a power supply and the electric motor, the plurality of power switches including a plurality of high-side switches and a plurality of low-side switches; and
a control unit configured to control a switching operation of the plurality of power switches to operate the electric motor and electronically brake the motor by simultaneously activating the plurality of the high-side switches or the plurality of low-side switches to apply a back-EMF (electro-magnetic force) current of the motor to the plurality of windings and thereby stop the rotation of the motor upon detection of a condition prompting the braking of the motor,
wherein the control unit is configured to electronically brake the motor over a plurality of braking cycles of the same time-length by executing a hard braking segment during which a first braking force is applied to brake the motor by supplying a first amount of motor back-EMF current to the plurality of stator windings, followed by a soft braking segment during which a second braking force is applied to brake the motor by supplying a second amount of motor back-EMF current to the plurality of stator windings, wherein the first braking force is greater than the second braking force and the first amount of motor back-EMF current per braking cycle is greater than the second amount of back-EMF current per braking cycle.
6. The power tool of claim 5 , wherein when executing soft braking, during a braking cycle, the control unit activates the three high-side switches or the three low-side switches simultaneously during a braking period, and deactivates all the plurality of power switches during a coasting period following the braking period.