How a Single Coil Powers Multiple Motor Armatures Simultaneously
A 1973 design for an electric motor that uses a single central coil to power several separate armatures arranged in a circle.
Original patent title: “Multi-armature motor”
A 1973 design for an electric motor that uses a single central coil to power several separate armatures arranged in a circle. Granted to Individual in 1973 with 8 claims and 22 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes a motor assembly where multiple armatures are placed in a circular pattern between two disks. These disks have interlocking finger-like projections that act as magnetic poles. A single central electromagnetic coil sits between the disks, creating a magnetic field that flows through these fingers to drive all the armatures at once. Essentially, it allows one power source to run multiple rotating parts simultaneously within a compact, integrated housing.
The gap
What does this patent NOT cover?
- Does not cover motors using permanent magnets instead of an electromagnetic coil.
- Does not cover linear motors where the armatures move in a straight line.
- Does not cover single-armature motors.
- Does not cover motors where the armatures are not arranged in a circular, parallel array.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The use of interdigitated finger portions creates a shared magnetic flux path, allowing one coil to effectively energize multiple independent armatures without needing individual coils for each one.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early multi-spindle industrial drills
Compact automated assembly line actuators
Why it matters
The bigger picture
This design represents an early attempt at high-density motor packaging. By sharing a single magnetic field source across multiple armatures, it aimed to reduce the weight and complexity of multi-motor systems, which is a common challenge in robotics and automated machinery.
Filed
March 20, 1972
Granted
March 27, 1973
Market context
Who's building on this
Companies in this space
Modern manufacturers of multi-spindle heads and synchronized robotic end-effectors continue to explore shared-flux motor designs to reduce weight in collaborative robots.
Market impact
While not a standard for mass-market consumer electronics, this patent influenced niche industrial engineering by demonstrating how to consolidate electromagnetic components, a principle now seen in high-density modular actuator design.
Claim 1 — Plain English
What this patent covers
This patent describes a motor assembly where multiple armatures are placed in a circular pattern between two disks. These disks have interlocking finger-like projections that act as magnetic poles. A single central electromagnetic coil sits between the disks, creating a magnetic field that flows through these fingers to drive all the armatures at once. Essentially, it allows one power source to run multiple rotating parts simultaneously within a compact, integrated housing.
The clever bit
The use of interdigitated finger portions creates a shared magnetic flux path, allowing one coil to effectively energize multiple independent armatures without needing individual coils for each one.
What it does not cover
- Does not cover motors using permanent magnets instead of an electromagnetic coil.
- Does not cover linear motors where the armatures move in a straight line.
- Does not cover single-armature motors.
- Does not cover motors where the armatures are not arranged in a circular, parallel array.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Early stage
Citation count
27/40
Moderately cited
Claim breadth
5/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$16K – $50K
Midpoint $32K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
8 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Mason, E. (1973). How a Single Coil Powers Multiple Motor Armatures Simultaneously (U.S. Patent No. 3,723,796). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3723796/mri-cancer-tissue-detection
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How a Single Coil Powers Multiple Motor Armatures Simultaneously cover?
A 1973 design for an electric motor that uses a single central coil to power several separate armatures arranged in a circle.
Who owns patent US 3723796?
Individual owns this patent, granted in 1973.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 3723796 cited by?
This patent has been cited by 22 later patents that build on its ideas.
What problem does this patent solve?
This design represents an early attempt at high-density motor packaging. By sharing a single magnetic field source across multiple armatures, it aimed to reduce the weight and complexity of multi-motor systems, which is a common challenge in robotics and automated machinery.
What does this patent NOT cover?
Does not cover motors using permanent magnets instead of an electromagnetic coil.
Same assignee
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