How Auto-Injectors Adjust Their Dose Using a Simple Spacer
A 1977 invention for auto-injectors that uses a physical spacer to adjust the amount of medicine inside the device before it is fired.
Original patent title: “Hypodermic injection device having means for varying the medicament capacity thereof”
A 1977 invention for auto-injectors that uses a physical spacer to adjust the amount of medicine inside the device before it is fired. Granted to Survival Technology Inc in 1977 with 7 claims and 108 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
This patent describes an auto-injector mechanism that allows the same device to hold different amounts of liquid medication. It achieves this by placing a spacer between the spring-loaded plunger and the piston inside the medicine cartridge. By changing the thickness or presence of this spacer, the piston is pushed further into the cartridge, effectively shrinking the volume of the medicament chamber. This ensures that the device can be calibrated for specific doses without needing to redesign the entire spring-power assembly.
The gap
What does this patent NOT cover?
- Does not cover electronic or digital dose-setting mechanisms
- Does not cover devices that use multiple chambers to mix medications
- Does not cover needle-free jet injection systems
- Does not cover the internal spring-power release mechanism itself
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
By using a spacer to pre-position the piston, the inventors decoupled the dose volume from the stroke length of the spring-powered plunger, allowing a single injector platform to be highly versatile.
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
EpiPen style emergency auto-injectors
Military nerve agent antidote injectors
Single-use pre-filled medication syringes
Why it matters
The bigger picture
This design was critical for the mass production of emergency auto-injectors, such as those used for nerve agent antidotes or epinephrine. It allowed manufacturers to use a standardized spring-loaded gun body while customizing the dose for different patient needs or drug concentrations using simple, interchangeable mechanical spacers.
Filed
May 14, 1976
Granted
June 28, 1977
Market context
Who's building on this
Companies in this space
Survival Technology Inc. was a pioneer in this space, and their work laid the foundation for modern auto-injector platforms. Today, major pharmaceutical and medical device companies like Pfizer, Mylan, and Becton Dickinson continue to refine these mechanical delivery systems for self-administration.
Market impact
This patent helped standardize the manufacturing of reliable, single-use emergency injectors. It enabled the widespread deployment of pre-filled, dose-specific injectors that could be safely used by non-medical personnel in high-stress environments.
Claim 1 — Plain English
What this patent covers
This patent describes an auto-injector mechanism that allows the same device to hold different amounts of liquid medication. It achieves this by placing a spacer between the spring-loaded plunger and the piston inside the medicine cartridge. By changing the thickness or presence of this spacer, the piston is pushed further into the cartridge, effectively shrinking the volume of the medicament chamber. This ensures that the device can be calibrated for specific doses without needing to redesign the entire spring-power assembly.
The clever bit
By using a spacer to pre-position the piston, the inventors decoupled the dose volume from the stroke length of the spring-powered plunger, allowing a single injector platform to be highly versatile.
What it does not cover
- Does not cover electronic or digital dose-setting mechanisms
- Does not cover devices that use multiple chambers to mix medications
- Does not cover needle-free jet injection systems
- Does not cover the internal spring-power release mechanism itself
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly 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
$99K – $317K
Midpoint $198K · expired or expiring · industry ×2.2
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
The original legal language
Original claims
7 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Kaplan, S., Calkins, G. B., Sarnoff, S. J., & Dalling, N. L. (1977). How Auto-Injectors Adjust Their Dose Using a Simple Spacer (U.S. Patent No. 4,031,893). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4031893/epipen-autoinjector-kaplan
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 Auto-Injectors Adjust Their Dose Using a Simple Spacer cover?
A 1977 invention for auto-injectors that uses a physical spacer to adjust the amount of medicine inside the device before it is fired.
Who owns patent US 4031893?
Survival Technology Inc owns this patent, granted in 1977.
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 4031893 cited by?
This patent has been cited by 108 later patents that build on its ideas.
What problem does this patent solve?
This design was critical for the mass production of emergency auto-injectors, such as those used for nerve agent antidotes or epinephrine. It allowed manufacturers to use a standardized spring-loaded gun body while customizing the dose for different patient needs or drug concentrations using simple, interchangeable mechanical spacers.
What does this patent NOT cover?
Does not cover electronic or digital dose-setting mechanisms
Patent monitoring