Exercise machine brake system

Abstract

An exercise machine includes a shaft configured to rotate about an axis; a spool configured to receive a strap and drive rotation of the shaft about the axis in response to movement of the strap; a flywheel configured to rotate about the axis; one or more conductive coils arranged to generate magnetic fields that induce eddy currents in the flywheel; a clutch configured to engage and disengage transmission of torque between the spool and the flywheel; and a spring arranged around the axis, the spring configured to exert a return torque on the spool about the axis in response to rotation of the shaft.

1 . An exercise machine, comprising:
 a brake shaft configured to rotate about a first axis;
 a spool configured to receive a strap and drive rotation of the brake shaft about the first axis in response to movement of the strap; 
 a flywheel configured to rotate about the first axis; 
 one or more conductive coils arranged to generate magnetic fields that induce eddy currents in the flywheel; 
 a clutch configured to engage and disengage transmission of torque between the spool and the flywheel; and 
 a spring configured to exert a return torque about a second axis in response to rotation of the brake shaft, wherein the second axis is different from the first axis. 
   
     
     
         2 . The exercise machine of  claim 1 , comprising:
 a gear stage sprocket configured to rotate together with the brake shaft about the first axis;   a spring shaft coupled to the spring, the spring shaft configured to rotate about the second axis;   a return stage sprocket configured to rotate together with the spring shaft about the second axis; and   a belt coupling the gear stage sprocket and the return stage sprocket.   
     
     
         3 . The exercise machine of  claim 2 , wherein the return stage sprocket has a larger radius than the gear stage sprocket. 
     
     
         4 . The exercise machine of  claim 2 , wherein the return stage sprocket has more teeth than the gear stage sprocket. 
     
     
         5 . The exercise machine of  claim 2 , comprising:
 a mechanical component holding the gear stage sprocket, the mechanical component pivotable with respect to the first axis to alter a distance between the first axis and the second axis.   
     
     
         6 . The exercise machine of  claim 5 , comprising one or more locking components adjustable to lock a position of the mechanical component with respect to the first axis. 
     
     
         7 . The exercise machine of  claim 1 , comprising a rowing exercise machine. 
     
     
         8 . The exercise machine of  claim 1 , wherein the spring comprises a torsion spring having a spiral shape. 
     
     
         9 . The exercise machine of  claim 1 , wherein the spool has a radius that increases in a winding direction of the spool. 
     
     
         10 . The exercise machine of  claim 1 , comprising an encoder configured to detect a positional parameter of the brake shaft. 
     
     
         11 . The exercise machine of  claim 10 , comprising:
 a spring shaft coupled to the spring, the spring shaft configured to rotate about the second axis in response to the return torque; and   a belt coupling the spring shaft and the brake shaft,   wherein the encoder is arranged on an opposite side of the belt from the flywheel.   
     
     
         12 . The exercise machine of  claim 1 , wherein the clutch is configured to engage and disengage transmission of torque between the flywheel and the brake shaft. 
     
     
         13 . The exercise machine of  claim 12 , wherein the clutch is arranged within a footprint of the flywheel. 
     
     
         14 . The exercise machine of  claim 3 , wherein a radius of the return stage sprocket is greater than two times a radius of the gear stage sprocket. 
     
     
         15 . The exercise machine of  claim 4 , wherein a tooth count of the return stage sprocket is greater than 2 times a tooth count of the gear stage sprocket. 
     
     
         16 . The exercise machine of  claim 1 , comprising:
 a spring shaft coupled to the spring, the spring shaft configured to rotate about the second axis in response to the return torque; and   a coupling between the spring shaft and the brake shaft, the coupling configured such that one full rotation of the spring shaft causes more than one full rotation of the brake shaft.   
     
     
         17 . The exercise machine of  claim 1 , wherein the brake shaft comprises an integrally-formed shaft extending to the spool and the flywheel. 
     
     
         18 . The exercise machine of  claim 1 , wherein the one or more conductive coils comprise two or more conductive coils arranged radially outside the flywheel. 
     
     
         19 . The exercise machine of  claim 1 , comprising a brake controller configured to adjust a current through the one or more conductive coils to set a braking force applied by the flywheel. 
     
     
         20 . The exercise machine of  claim 19 , wherein the brake controller is configured to:
 receive, as input, sensor data indicative of rotation of the brake shaft;   apply the sensor data to a stored model of the exercise machine; and   determine, as an output of the stored model, the current.