Weight machine sensor system
A load sensor includes a bolt configured to support a pulley of a weight machine, and a strain gauge laminated onto an exterior surface of a shoulder section of the bolt.
1. A weight machine sensor system for determining a weight setting of a weight machine having weight plates and incremental weights to be lifted during an exercise, the weight machine sensor system comprising:
a load sensing bolt configured to support a pulley of the weight machine and including a strain gauge for sensing force transferred from the weight plates and the incremental weights by the pulley to the load sensing bolt; and
a controller in communication with the load sensing bolt, wherein the controller determines a weight setting of the weight machine according to the load sensing bolt.
2. The weight machine sensor system of claim 1 , wherein the strain gauge is laminated onto an exterior surface of a shoulder section of the bolt for sensing force applied by the pulley to the bolt.
3. The weight machine sensor system of claim 2 , wherein the bolt is configured to orient the strain gauge relative to the weight machine.
4. The weight machine sensor system of claim 3 , wherein the bolt includes an alignment feature the shaft to control orientation of the strain gauge relative to the weight machine, the alignment feature being a flat face of the shoulder section of the bolt.
5. The weight machine sensor system of claim 4 , wherein the alignment feature of the bolt mates with a corresponding alignment feature of a bracket of the weight machine, the corresponding alignment feature being a non-circular through-hole that mates with the alignment feature of the bolt to control the orientation.
6. The weight machine sensor system of claim 3 , wherein the bolt is configured to orient the load sensor with the strain gauge being in one of tension or shear when the pulley is loaded.
7. The weight machine sensor system of claim 2 , wherein the shoulder section includes a stress concentration geometry proximate the strain gauge.
8. The weight machine sensor system of claim 7 , wherein the stress concentration geometry axially overlaps the strain gauge.
9. The weight machine sensor system of claim 8 , wherein the stress concentration geometry is a recess extending circumferentially at least partially around an axis of the bolt.
10. The weight machine sensor system of claim 2 , wherein the shoulder section includes a stress concentration geometry that axially overlaps the strain gauge, the stress concentration geometry being a recess extending circumferentially at least partially around an axis of the bolt;
wherein the bolt is configured to orient the strain gauge relative to the weight machine in a predetermined orientation, the bolt including an alignment feature that is a flat face of the shoulder section that mates with a corresponding alignment feature of a bracket of the weight machine, the corresponding alignment feature being a non-circular through-hole;
wherein the predetermined orientation includes the strain gauge being in one of tension or shear when the pulley is loaded.
11. The weight machine sensor system of claim 1 , further comprising an incremental weight sensor configured to sense the one or more incremental weights lifted during an exercise, wherein the controller is in communication with the incremental weight sensor and determines the weight setting of the weight machine according to the load sensing bolt and the incremental weight sensor.
12. The weight machine sensor system of claim 11 , wherein the controller calculates a weight measurement value from the force sensed by the load sensing bolt, and determines the weight setting with a rounding algorithm according to the weight measurement value and a signal received from the incremental weight sensor indicating the incremental weights lifted during the exercise.
13. The weight machine sensor system of claim 12 , wherein the rounding algorithm accounts for weight values, numbers, and sequencing of the weight plates.
14. The weight machine sensor system of claim 1 , wherein the controller calculates a weight measurement value from the force sensed by the load sensing bolt, and determines the weight setting by rounding the weight measurement value.
15. The weight machine sensor system of claim 14 , wherein the load sensing bolt is calibrated to the weight machine, and the controller determines the weight measurement value according to a force value output by the load sensing bolt from sensing the force and a weight function determined when the load sensing bolt was calibrated to the weight machine, the force value being a voltage.
16. A method for retrofitting a weight machine with a weight machine sensor system that is configured to determine a weight setting of the weight machine during an exercise, the weight machine being of a type having a weight stack with weight plates that are to be lifted during the exercise, the method including:
providing a weight machine sensor system that includes a load sensing bolt and a controller;
replacing a pulley bolt of the weight machine with the load sensing bolt to support a pulley of the weight machine, the load sensing bolt being configured to sense force applied by the pulley thereto; and
calibrating the load sensing bolt to determine a weight function by which a weight measurement value is capable of being determined from a force value output by the load sensing bolt.
17. The method of claim 16 , wherein the weight machine is of a type having incremental weights that are selectively lifted with the weight plates of the weight stack during the exercise, the weight machine sensor system includes an incremental weight sensor, and the method further includes installing the incremental weight sensor to the weight machine;
wherein the incremental weight sensor is configured to sense which of the incremental weights are lifted during the exercise; and
wherein the calibrating includes lifting the weight stack at different weight settings, measuring force values at the different weight settings, and determining the weight function according to the force values and the different weight settings.
18. The method of claim 16 , wherein the weight machine is of a type having incremental weights that are to be selectively lifted with the weight plates of the weight stack during the exercise, and the weight machine sensor system includes an incremental weight sensor, the method further comprising:
installing the incremental weight sensor to the weight machine, the incremental weight sensor being configured to sense which of the incremental weights of the weight machine are lifted during the exercise.
19. The method of claim 16 , wherein the calibrating includes lifting the weight stack at different weight settings, measuring force values at the different weight settings, and determining the weight function according to the force values and the different weight settings.
20. The method of claim 19 , wherein the lifting of the weight stack is performed with a calibration tool that includes a rigid frame, first and second pulleys fixed to the rigid frame, and a third pulley movable relative to the first and second pulleys to effectively shorten a cable and, thereby, lift the weight stack, the third pulley being movable along a threaded rod by an electric motor.