Power Tool With Dynamic and Mechanical Brake

Abstract

A power tool in accordance with an embodiment of the invention has a motor driving a member, a switch coupled across windings of the motor that dynamically brakes the motor, and a mechanical brake that brakes speed of the member. In an aspect, the combined dynamic and mechanical braking brakes speed of the member to a desired speed in no more than about two second. In an aspect, the motor is an electronically commutated motor and the power tool includes a controller that electronically commutates the motor by switching switches that switch power to the motor in an electronic commutation sequence and switches the switches to electronically brake the motor.

1 . A power tool, comprising: 
 a motor driving a member;    a switch coupled across windings of the motor that dynamically brakes the motor;    and a mechanical brake that brakes speed of the member.    
   
   
       2 . The apparatus of  claim 1  wherein the combined dynamic and mechanical braking brakes speed of the member to a desired speed in no more than about two seconds.  
   
   
       3 . The apparatus of  claim 2  wherein the desired speed is stop.  
   
   
       4 . The apparatus of  claim 2  wherein the desired speed is an idle speed.  
   
   
       5 . The apparatus of  claim 1  including a resistor that is coupled across windings of the motor by the switch in dynamically braking the motor.  
   
   
       6 . The apparatus of  claim 1  wherein the switch shorts the motor windings to dynamically brake the motor.  
   
   
       7 . A power tool, comprising: 
 an electronically commutated motor driving a member;    a motor controller that electronically commutates the motor by switching switches that switch power to the motor in an electronic commutation sequence and switches the switches to electronically brake the motor; and    a mechanical brake that brakes speed of the member.    
   
   
       8 . The apparatus of  claim 7  wherein the controller switches the switches to short a winding of the motor to electronically brake the motor.  
   
   
       9 . The apparatus of  claim 7  wherein the combined electronic and mechanical braking brakes speed of the member to a desired speed in no more than about two seconds.  
   
   
       10 . The apparatus of  claim 9  wherein the desired speed is stop.  
   
   
       11 . The apparatus of  claim 9  wherein the desired speed is an idle speed.  
   
   
       12 . The apparatus of  claim 7  including a resistor that is coupled across windings of the motor when the motor controller electronically brakes the motor.  
   
   
       13 . The apparatus of  claim 7  including an on/off switch and the motor controller sensing collapse of an input voltage when the on/off switch is turned off and switching the switches to electronically brake the motor.  
   
   
       14 . The apparatus of  claim 13  wherein the mechanical brake mechanically braking the member and the motor controller electronically braking the motor brakes speed of the member to a desired speed in no greater than about two seconds.  
   
   
       15 . The apparatus of  claim 14  wherein the desired speed is stop.  
   
   
       16 . The apparatus of  claim 14  wherein the desired speed is an idle speed.  
   
   
       17 . The apparatus of  claim 13  including a resistor that is coupled across windings of the motor when the motor controller electronically brakes the motor.  
   
   
       18 . The apparatus of  claim 7  wherein the motor controller switches the switches to reverse commutate the motor to electronically brake the motor.