Exercise apparatus with linear positioning system

1. A strength training assembly, comprising:

a stand;

a frame movable along the stand in a vertical direction, the frame comprising a cradle configured to receive a barbell such that an upward force on the barbell lifts the barbell away from the cradle for performance of an exercise using the barbell;

a drive system coupled to the frame and controllable to affect a velocity of the frame relative to the stand;

a force sensor coupled to and movable with the frame, the force sensor configured to provide a signal indicative of force exerted on the force sensor by a user; and

a controller configured to receive the signal from the force sensor and control the drive system such that the velocity of the frame varies as a function of the force exerted on the force sensor.

2. The strength training assembly of claim 1 , wherein the drive system comprises:

an electric motor coupled to the stand; and

a belt connected to the electric motor such that the electric motor is configured to cause rotation of the belt;

wherein the belt is coupled to the frame such that rotation of the belt causes movement of the frame relative to the stand.

3. The strength training assembly of claim 1 , wherein:

the stand comprises a vertical rail; and

the frame is slideably mounted on the vertical rail.

4. The strength training assembly of claim 1 , wherein the force sensor is static relative to the frame, and wherein the barbell is configured to move relative to the force sensor during the performance of the exercise using the barbell.

5. The strength training assembly of claim 1 , wherein the controller is configured to control the drive system such that the velocity of the frame varies as the function of an amount and direction of the force exerted on the force sensor by controlling the drive system to provide an exponential relationship between the amount of force exerted on the force sensor and the velocity of the frame.

6. The strength training assembly of claim 5 , wherein controlling the drive system to provide the exponential relationship between the amount of force exerted on the force sensor and the velocity of the frame further comprises providing a deadband such that the controller causes the drive system to prevent movement of the frame when the amount of force exerted on the force sensor is less than a threshold magnitude.

7. The strength training assembly of claim 1 , wherein the strength training assembly further comprising a digital force production system coupled to the stand and different than the drive system operable to affect the velocity of the frame relative to the stand, the digital force production system comprising:

a plurality of cables coupled to the barbell, the barbell configured to be selectively received by and removed from the pair of cradles with the plurality of cables remaining coupled to the barbell when the barbell is removed from the pair of cradles; and

a plurality of actuators configured to provide tension to the plurality of cables.

8. A linear positioning system, comprising:

a load mounted on a rail;

an actuator controllable to cause movement of the load along the rail;

a force sensor rigidly coupled to the load such that the force sensor moves with the load, wherein the force sensor is configured to measure an amount of force exerted on the force sensor by a user; and

a controller configured to control the actuator to provide the load with a velocity that varies as a function of the amount of force measured by the force sensor, wherein the load comprises a pair of cradles configured to receive and support a barbell such that an upward force on the barbell lifts the barbell away from the pair of cradles without affecting the force on the force sensor.

9. The linear positioning system of claim 8 , wherein the function comprises an exponential function of the amount of force.

10. The linear positioning system of claim 8 , wherein the controller is configured to control the actuator such that:

when the amount of the force is within a deadband, the velocity is zero; and

when the amount of the force is outside the deadband, a magnitude of the velocity increases continuously as the amount of force increases.

11. The linear positioning system of claim 10 , wherein the force sensor is configured to determine whether the force is exerted on the force sensor in a first direction or a second direction opposite the first direction; and

wherein the controller is configured to control the actuator such that:

when the force is in the first direction, the velocity is in the first direction; and

when the force is in the second direction, the velocity is in the second direction.

12. The linear positioning system of claim 8 , wherein the controller is configured to:

calculate a target velocity based on the amount of force exerted on the force sensor using the function; and

cause the velocity of the load to track the target velocity.

13. The linear positioning system of claim 12 , further comprising a velocity sensor configured to determine the velocity of the load, wherein the controller is configured to provide enable feedback control based on the target velocity and measurements from the velocity sensor.

14. The linear positioning system of claim 8 , wherein the actuator comprises an electric motor.

15. The linear positioning system of claim 14 , wherein the controller is configured to control the actuator by varying a voltage provided to the electric motor based on a magnitude of a signal received from the force sensor.

16. The linear positioning system of claim 8 , wherein the barbell is coupled to a force production system comprising a plurality of cables, wherein tension in the plurality of cables provides resistance for an exercise using the barbell separate from operation of the actuator.

17. A strength training assembly, comprising:

a stand;

a frame movable along the stand in a first direction and an opposite second direction, the frame comprising a pair of cradles configured to receive a barbell;

an electric motor operable to provide motorized adjustment of a position of the frame relative to the stand to adjust a starting position of the barbell for an exercise, wherein the barbell is lifted out of the cradles by a user during performance of the exercise; and

a digital force production system coupled to the stand and different than the electric motor operable to provide motorized adjustment of the position of the frame relative to the stand, the digital force production system comprising:

a plurality of cables coupled to the barbell, the barbell configured to be selectively received by and removed from the pair of cradles with the plurality of cables remaining coupled to the barbell when the barbell is removed from the pair of cradles; and

a plurality of actuators configured to provide tension to the plurality of cables.

18. The strength training assembly of claim 17 , further comprising a controller configured to:

determine a target for the position of the frame based on a selected exercise or a user profile; and

control the electric motor to adjust the position of the frame to match the target.

19. The strength training assembly of claim 17 , further comprising a user input device mounted on the frame and configured to allow the user to request movement of the frame by the electric motor.

20. The strength training assembly of claim 19 , wherein the electric motor is configured to prevent movement of the frame relative to the stand unless the user input device is engaged by the user.

21. The strength training assembly of claim 17 , wherein the frame is movable by the electric motor while the barbell is supported by the pair of cradles.