The Umbrella Frame: Springs That Hold It Open and Hold It Shut

"This invention has for its object improvements in umbrellas, parasols, and sun-shades of that kind which do not have catches to hold them open and closed." Hoyland employs "an additional or intermediate runner, sliding upon the stick between the ordinary runner which receives the ends of the stretchers and the top notch to which the ends of the ribs are jointed. This intermediate runner I connect by links to the stretchers." The spring "bears upon a cross-bar, which connects the two links together at a short distance from the joint, and tends to press the cross-bar toward the stretcher". "As the umbrella, parasol, or sun-shade is opened by sliding the main runner up the stick, the links and the stretchers separate until they become perpendicular, and when the umbrella, parasol, or sun-shade is fully open they have passed this position and begun again to close together". Closed, the springs keep "the stretchers and links parallel and closed together. This compels them, and also the ribs, to lie close in against the stick, so that no fastening is required to keep the umbrella closed." Open, "the intermediate runner is made of such a length that it serves as a stop or abutment for the main runner".

Take a stick umbrella with a runner catch and one without, if you have both. Hook a spring scale to the runner and pull it up the stick slowly, reading the force every 2 cm, measured with a tape along the stick. Do the same closing. Plot force against runner position. A frame that holds itself shows a peak and then a force that reverses sign near the end: it pulls itself open. A frame with a catch rises smoothly and needs the catch. Measure the angle between a stretcher and rib at the reversal with a protractor. Open umbrellas away from faces: rib tips are at eye height.

**William Hoyland** of Eckland Bridge Works, near Penistone, Yorkshire, England, filed US 217,533 on 8 April 1879; it is dated 15 July 1879 and notes an English patent of 2 August 1878. **Honest limits.** The patent gives no dimensions or spring strengths. The spring model is the simplest shape that shows two stable positions; the spring stiffness, lever, stop angle and drag coefficient are examples.