Knee lever

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Bolt cutter: opening and closing with the toggle principle

The toggle lever consists of at least two jointly connected lever elements. As with every lever, according to the law of the lever, a long stroke with low pulling or pushing force is converted into a small stroke with high force or vice versa (force multiplier ).

The special feature of the toggle lever principle is that the transmission ratio between the applied force and the resulting force or from the primary stroke to the secondary stroke shifts continuously during the movement. This makes it possible, for example in a toggle press, to bring the ram quickly up to the material to be pressed, then to compress the material to be pressed at medium speed and medium pressure, and finally to complete the pressing process at low speed and very high pressure.

In the bent state, the toggle lever causes a high path transmission with a low force transmission. The closer the toggle lever approaches the extended state, the more the lifting speed decreases while the operating speed remains the same, while the pressing force increases. With the knee lever extended, the force theoretically approaches infinity.

Significance of the knee lever in mechanical engineering

The toggle lever principle is used when rapid movement and later high power transmission is required. This is the case, for example, when the air contained in a porous material is first to be pressed out before a higher pressing force is required in order to further deform the now compact material. Or when, during a clamping process, a certain distance is to be passed through in idle mode before the workpiece to be fixed is reached.

The following effects are combined in one knee lever:
  • A mechanically integrated deceleration ramp with constant actuation speed.
  • A very high power transmission over the last millimeters of the ram travel.
  • When the toggle lever is overstretched (past dead center ), a locking effect can be achieved if a mechanical stop is present. Even if the actuation force drops, the clamping force is maintained and the clamped workpiece cannot release itself.

Elastic elements (springs) can be used to limit the pressing force and to compensate for tolerances.

Inventions

Crossbow tensioner with toggle lever in the 16th century
Clamp by pressing the knee lever

The invention of the toggle lever is associated with the invention of the toggle press for the purpose of coinage . Diedrich Uhlhorn is listed as a German inventor in Grevenbroich in 1817 .

“Efforts by English and French mechanics to replace the hydraulic press with other presses that also work noiselessly (silently) without impact have been unsuccessful, especially Hallett's press with eccentric discs and the toggle presses from Sudds, Barker, Atkin's and others are. The advantage of such presses, that the pressing force increases with the increasing resistance of the bodies to be pressed, is completely outweighed by the greater friction and the associated wear and tear compared to hydraulic presses, so that they can be regarded as lost to history. "

- Polytechnical journal
  • In 1811, the Russian I. Nevedomsky presented the invention of a toggle press in St. Petersburg .
  • If we go back further in history, in the 16th century there is a toggle lever attached to the crossbow as a tensioning aid for the bowstring of the strong metal bow.
  • As early as the 15th century , resourceful armourers were producing the goat's foot lever for quickly cocking the crossbow. This first known, attachable toggle lever consisted of a two-pronged fork with an extension handle. The pulling claw for the bowstring was stored in the lower third . With the extension handle, the “goat foot lever”, which was mounted on the crossbow shaft by the fork prongs on a spike , was pulled to the shooter and the pulling claw pulled the bowstring up to the locking nut. The further the string was stretched, the smaller the lower (fork) lever became. Despite the increasing tensile force of the bow, the toggle effect reduced the force on the draw lever for the shooter. Another version was designed for pressure.

Structure and applications

The structure is comparable to that of a human knee joint . It consists of three pivot points and at least two legs. In the human knee joint, it is the hip joint , the knee joint and the ankle joint , which are connected by the lower and upper thighs.

It is used, for example, on toggle presses in letterpress printing and on fruit presses to increase pressure . For lifting movements, it is used as a scissor car jack .

A toggle lever can be found on a wide variety of tools, such as hand tin snips , locking pliers , punch pliers and much more.

A toggle lever is often used for tensioning and is overstretched to lock :

  • Actuation by pressure

  • Toggle press

  • Jack with double knee lever

  • Lever metal shears

  • Pipe cutter

  • Hand tin snips

  • One-armed jack

  • Six-armed polyp grasper

  • Knee joint lock of a firearm

  • Ski boot with toggle clamps (in blue and green)

  • Crate lock

  • Swing top on a beer bottle

  • Springform closure

  • Folding clasp on wristwatches

  • Actuation by pulling

  • Round material gripper (lifting tongs)

  • The centrifugal governor with two-sided toggle lever has been used in mechanical engineering since 1788.

literature

Web links

Individual evidence

  1. ^ Rühlmann, Moritz: Contribution to the history of the oil mills. In: Polytechnisches Journal . 178, 1865, pp. 258-277. (Inventors: the English Sudds, Barker and Atkins)
  2. ↑ G. Lutz, O. Heller, Felix Kassler: Technology of fats and oils. Handbook of the extraction and processing of fats, oils and waxes of the plant and animal kingdom . Volume 1, page 247 ( limited preview in Google Book search).
  3. ↑ Pressing (in technology) . In: Brockhaus Konversations-Lexikon 1894-1896, Volume 13, p. 376. Inventor: the Russian I. Nevedomsky, 1811 in St. Petersburg for coinage
  4. ↑ Fig. 43 (picture of the tensioning process) The Crossbow Chapter XVII, The Mechanism of the Goat's-Foot Lever and Fig. 44. ( Detailed picture) - The Mechanism of the Goat's-Foot Lever. Half full size. From: Ralph Payne Gal, Sir Ralph Payne Gallwey: Crossbow . Naval and Military Press, 2009, ISBN 1-84342-833-4
  5. ↑ Fig. 106 (picture, pushing the bowstring) A wooden goat foot lever tensions by pressing on the bowstring. (The Crossbow, p. 167)
  6. ↑ Spring-loaded body fittings on drop sides ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.9 MB) @1@ 2Template: Webachiv / IABot / www.titgemeyer.dk