Station-Indicator (Thomas W. Stewart & William Edward Johnson, No. 499,895)
The patent describes a Station-Indicator designed for railway cars and street cars. The main object of the invention is to automatically operate the signal (i.e., advance the station name display) using a mechanical lever on the car that interacts with an inclined projection (block) positioned alongside the track.
Invention and Mechanism
The indicator is a complex, fully mechanical system that combines a roller sign display with an automated track-side trigger:
- Display Mechanism:
- Frame (A, B): A case fixed inside the car (e.g., on the wall).
- Shafts (C, D): Two shafts that hold the indicator belt.
- Indicator Belts (E): Flexible belts wound onto the shafts. They feature two separated strips connected by posts (c), allowing cards bearing the names of stations or streets to be inserted through a slot (e) and displayed through a window (F).
- Actuation (Advancing the Display):
- Gears (G, H, I): Gears H and G are on the shafts C and D, respectively. A central gear I meshes between them, transmitting motion.
- Ratchet and Pawl System: Gears H and I have ratchets (a,b) and radial arms (c,e) with pivoted dogs (h,i).
- Connecting Bar (f): Pivotally connects the ends of the radial arms (c,e).
- Track-Side Trigger: An elbowed lever (2) with a small wheel (3) is attached to the car in a position to traverse the track rail.
- Inclined Block (M): A stationary, inclined block is placed beside the track rail at the approach to each station.
- Operation: When the car approaches a station, the wheel (3) on the lever (2) runs onto the block (M). This contact trips the lever (2), which pulls a connecting cord, chain, or cable (r). This cable, in turn, operates the connecting bar (f), causing the engaged dog/pawl (h or i) to turn the shafts (C, D) a distance equal to one card width, advancing the next station name into the viewing window (F).
- Jar Prevention: A spring (4) and an elongated slot are incorporated into the connection (r) to prevent normal track vibration or jar from accidentally operating the mechanism.
- Direction Reversal:
- Rocking Lever (m): Centrally pivoted to the connecting bar (f), with slots in each end.
- Forked Lever (n): A pivoted lever with a handle (p). Its ends loosely engage the slots of the rocking lever (m).
- Reversal Action: When the car reaches the end of the line, the operator uses the handle (p) to move the forked lever (n). This rocks the lever (m) which pushes against the rearward extensions (j,k) of the dogs (h,i), causing one dog to disengage from its ratchet and the other dog to engage. This reverses the direction the indicator belt travels, preparing it for the return trip.
- Additional Features:
- Pneumatic Alarm Bell: An elbowed arm (5) connected to the bar (f) enters a case (t) and operates a pneumatic alarm bell to audibly announce the station change.
- Belt-Tensioning Device: Rollers (6) with springs (9) are mounted in the frame to hold the display belts taut against the viewing opening (F).
- Rules/Instructions Display: An optional endless belt (S) displaying company rules and regulations can be attached, geared to shaft G, and displayed simultaneously with the station name.
Historical Significance and the Inventors
The patent by Thomas W. Stewart and William Edward Johnson of Detroit, Michigan, is a pivotal example of automation in public transit during the late 19th century.
- Addressing a Key Transit Need: Prior to automated systems, station announcements relied solely on the conductor shouting the names. In noisy or crowded streetcars and railway cars, this was often unreliable, leading to missed stops and passenger confusion. This invention was one of many attempts to solve this problem mechanically.
- The Rise of Automation: The late 1800s saw a massive expansion of public transit, especially electric streetcars. This system’s reliance on a track-side trigger (block M) and a car-mounted mechanical arm (lever 2) was a common approach for automated systems before the widespread adoption of electricity and later electronics for signaling and control.
- The Inventors: Thomas W. Stewart was also the inventor of the Mop patent (No. 499,402). The collaboration with William Edward Johnson and the assignment of half interest to Levi H. Johnson and Albert H. Johnson (likely businessmen or investors) is typical of the era, where inventors partnered with those who could provide capital or manufacturing expertise to bring their complex mechanical devices to market.
Relation to Current Items
Stewart and Johnson’s indicator pioneered functions that are standard in modern transportation:
- Automated Announcements and Displays: The core function of providing both a visual display (belts E) and an audible signal (pneumatic bell) upon approaching a stop is the blueprint for modern Public Address (PA) systems and digital LED or LCD passenger information displays used in all modern subways, buses, and trains.
- Track-Based Triggering: The use of an external element (the inclined block M) to automatically trigger an on-board event is the foundational concept for many modern railway safety and signaling systems, such as:
- Automatic Train Control (ATC): Systems that use transponders, magnets, or inductive loops embedded in or beside the track to communicate vital speed and location data to the train’s computer.
- Positive Train Control (PTC): Advanced systems that monitor and control train movements based on GPS and wayside communication to prevent collisions and over-speed events.
- Roll-Sign Displays: The use of a belt that winds from one shaft to another to present information is the exact mechanism employed by legacy destination roll signs still found on older buses and transit vehicles globally, though they are increasingly being replaced by digital displays.
