US 4,934,694 · Granted 1990-06-19
The 1990 Patent That Made Exercise Machines Smart
A computer-controlled exercise machine that uses a motor and position sensor to adjust how hard you're working in real time. Instead of just lifting the same weight every rep, the machine's computer changes the resistance based on where your arm or leg is and what the program tells it to do.
The plain-English version
What it protects
The claim covers a system where a DC motor drives an exercise arm or lever, with an encoder (position sensor) that tracks exactly where the limb is at every moment. A computer reads that position and adjusts the electrical current flowing through the motor to increase or decrease resistance on the fly. What's protected is this specific combination: the direct mechanical coupling between motor and exercise member, plus the closed-loop feedback system that varies torque based on angular position and preprogrammed instructions.
Why it matters
This patent represents an early approach to adaptive resistance training—the idea that a machine can respond intelligently to an athlete's movement rather than providing fixed resistance. By patenting the method of using position feedback to modulate motor torque, it established intellectual property around computer-controlled exercise systems. This laid groundwork for modern machines that adjust difficulty mid-rep and can simulate realistic force curves matching how real weights behave.
Real-world use
When you use a modern cable machine or leg press that seems to know exactly when to push back harder or easier as you move through your range of motion, you're experiencing the logic this patent protects.
Original USPTO abstract
A DC motor is connected to a driveshaft the rotation of which is directly coupled to movement of an exercise member. The DC motor is operated in the current control mode wherein current direction and value through the winding of the motor determines its torque. An encoder is connected to the shaft of the motor to monitor its angular position. A program controlled processor monitors the angular position of the shaft and controls the current to the motor to vary the torque thereof and, thus, the force of resistance or assistance to the exercise member in accordance with preprogrammed values and as a function of angular position. A plurality of encoder/motor assemblies control exercise about a plurality of axes of bodily movement.
Patent details
- Publication number
- US 4,934,694
- Filing date
- 1988-03-09
- Grant date
- 1990-06-19
- Assignee
- Mcintosh James L
- Inventor(s)
- MCINTOSH; JAMES L.
- CPC class
- B23P19/066
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