US 4,891,764 · Granted 1990-01-02
The Smart Force Detector That Measures Workout Resistance Without Strain Gauges
Imagine a robot arm that can figure out exactly how hard something is pushing back against it—not by adding extra sensors, but by being clever about electricity and motion. This patent uses a microprocessor to send current through an electric motor, then watches how fast it speeds up or slows down to calculate the invisible forces fighting against it.
The plain-English version
What it protects
The claim covers a computerized system that measures opposing forces by controlling the electrical current through an actuator and using a motion sensor to track velocity and acceleration. What's protected here is the method of balancing electromagnetic force against unknown resistance forces so that when acceleration hits zero, the computer can calculate the exact opposing force without needing a separate pressure or load sensor.
Why it matters
This patent solves a real engineering problem: measuring force in tight spaces or during high-speed motion where traditional strain gauges don't work well. By letting software do the math instead of hardware, the system becomes cheaper, more compact, and easier to integrate into machines. This approach opened doors for smarter actuators in robotics, industrial automation, and exercise equipment.
Real-world use
Modern smart fitness equipment and resistance machines use this principle to measure how hard you're pushing or pulling without needing bulky mechanical load cells built into every joint.
Original USPTO abstract
A microprocessor based electric actuator control system is provided which allows accurate determination of the forces opposing movement of manipulator driveshaft. The control system electronically sets a predetermined current through an actuator to produce an electromagnetic force. A displacement measuring device, in conjunction with a time clock measures velocity and calculates acceleration of the actuator in response to the current. The force on the shaft is computer varied such that the acceleration is determined. For the acceleration to be zero, the electromagnetic force be exactly balanced by forces equal but opposite in magnitude. Since the force value is determined by the computer, the opposing force is also accurately determined with no external sensing device needed.
Patent details
- Publication number
- US 4,891,764
- Filing date
- 1987-12-11
- Grant date
- 1990-01-02
- Assignee
- Tensor Development Inc.
- Inventor(s)
- MCINTOSH; JAMES L.
- CPC class
- G05B19/237
Want to file your own patent?
If you're designing the next generation of smart gym equipment, search our patent database to see what force-sensing innovations are already locked down by competitors.
Free patentability scan