Riefler escapement

The Riefler escapement is a mechanical escapement for precision pendulum clocks invented and patented [German patent no. 50,739] by Sigmund Riefler in 1889. [cite book
last =
first =
authorlink =
coauthors =
title = Special Catalog of the Joint Exhibition of German Mechanicians and Opticians, Section 3, Class 15, International Exposition, Paris 1900
publisher = Reichsdruckerei
date = 1900
location = Berlin
pages =
url = http://books.google.com/books?id=75MAAAAAMAAJ&pg=PA36
doi =
id =
isbn = p.36] It was used in the astronomical regulator clocks made by his German firm Clemens Riefler from 1890 to 1965,cite book
last = Day
first = Lance
authorlink =
coauthors = Ian McNeil
title = Biographical Dictionary of the History of Technology
publisher = Routledge
date = 1996
location = New York
pages =
url = http://books.google.com/books?id=qNp3JM35UMoC&pg=PA602
doi =
id =
isbn = p.602] which were perhaps the most accurate all-mechanical pendulum clocks made.

An escapement is the mechanism in a mechanical clock that gives the pendulum precise impulses to keep it swinging, and allows the gear train to advance a set amount with each pendulum swing. The Riefler escapement was an improvement of the deadbeat escapement, the standard used in precision clocks. In the deadbeat, the force to keep the pendulum swinging is applied by the teeth of the escape wheel sliding alternately against two angled pallets on arms attached to the pendulum. Therefore, slight variations in the friction of the pallets and in the torque from the escape wheel are passed on to the pendulum, disturbing its motion.

How it works

In the Riefler escapement, the energy required to keep the pendulum swinging is instead supplied by bending the short spring strip which suspends the pendulum.cite book
last =
first =
authorlink =
coauthors =
title = German Exhibition, Group 21, Special Catalog of the Collective Exhibition of Scientific Instruments and Appliances, Columbian Exposition, Chicago, 1893
publisher = Deutsche Gesellschaft fur Mechanik und Optik
date = 1893
location = Berlin
pages =
url = http://books.google.com/books?id=6NU4AAAAMAAJ&pg=PA64
doi =
id =
isbn = p.64] The pendulum is not suspended from a fixed support, but instead the upper end of the suspension spring is attached to a heavy metal bearer, which pivots on two aligned knife-edges on its underside. The bending point of the suspension spring is in alignment with the line of contact of the knife-edges and the planes or supports on which they rest. When the pendulum passes its bottom point, the escape wheel is unlocked and pushes the bearer, and the bearer pivots suddenly on its knife edges by a small angle, flexing the spring. The spring is bent by a small amount in addition to that caused by the swing of the pendulum, and thus provides the impulse for the next swing. So the suspension spring is used for two functions: suspending the pendulum and giving it impulse.

The escapement has better performance than the deadbeat because the force from the pallets, with its variability, is applied not to the pendulum but to the bearer. The escapement has no contact with the pendulum below the suspension spring. The pendulum is free of disturbance from the escape wheel for roughly two-thirds of each swing,Fact|date=May 2008 and the only work it has to do is to unlock the escape wheel once per second. This operation is performed near the ideal place, at the center of each swing.

The Riefler escape wheel and pallets are of a special design. There are actually two escape wheels mounted on the same shaft and two surfaces on each of the two pallet pins. The front locking wheel has forward pointing teeth rather like a dead-beat escapement, and catches on the flat surface of the pallet to lock the wheel. The rear impulse wheel has teeth with a sloping surface facing the direction of rotation. The round part of each pallet is acted upon by this surface to give the impulse.

Riefler clocks

Clemens Riefler astronomical regulator clocks achieved accuracies of 10 milliseconds per day.cite conference
last=Sullivan
first=D.B.
title=Time and frequency measurement at NIST: The first 100 years
date=2001
booktitle=2001 IEEE Int'l Frequency Control Symp.
publisher=National Institute of Standards and Technology
url=http://tf.nist.gov/timefreq/general/pdf/1485.pdf p.4-5] cite web
date=2002
title=A Revolution in Timekeeping, part 3
work=A Walk Through Time
publisher=NIST (National Inst. of Standards and Technology)
url=http://physics.nist.gov/GenInt/Time/revol.html
accessdate=2007-06-06] and were guaranteed to be within 30 milliseconds. [cite web
title = Clemens Riefler regulator, 1929
work = [http://www.nawcc.org/museum/nwcm/galleries/precision/precision.htm Precision Regulator Clocks Gallery] , National Watch and Clock Museum
publisher = NAWCC (National Association of Watch and Clock Collectors)
date = 2007
url = http://www.nawcc.org/museum/nwcm/galleries/precision/riefler.htm
accessdate = 2008-06-02] With over 600 made, they were one of the most widely used astronomical regulators, and became the highest standard for timekeeping in the early 20th century. They were used worldwide in astronomical observatories, naval observatories, and as primary standards for electrical time dissemination services, which delivered time signals by telegraph wire. Riefler clocks had internal switch contacts for this purpose, which delivered a 1 Hz time signal to external equipment. The first time standard for the Unites States, provided by the Bureau of Standards (now NIST), was from 1904 to 1929 generated by Riefler clocks.

Working Riefler precision pendulum clocks on display to the public are located at the Deutsches Museum in Munich, the National Watch and Clock Museum in Columbia PA, the Musée international d'horlogerie pn La Chaux-de-Fonds, the Musée d'horlogerie in Le Locle, the Deutsches Uhrenmuseum in Furtwangen, and at the US Naval Observatory(by appointment only) in Washington DC.

External links

*cite web
last =
first =
authorlink =
coauthors =
title = Riefler astronomical regulator No. 65,
work = inventory no. 1998-1-0190a
publisher = History of Science Dept., Harvard Univ.
date =
url = http://dssmhi1.fas.harvard.edu/emuseumdev/code/emuseum.asp?style=text&currentrecord=1&page=seealso&profile=objects&searchdesc=Related%20to%20Sigmund%20Riefler...&searchstring=seealsoid/,/is/,/70/,/false/,/true&sessionid=672752EF-3AEB-47FE-8F3D-128257C508F4&action=searchrequest&style=single&currentrecord=1
format =
doi =
accessdate = 2008-05-31 Pictures of 1902 Riefler clock and its parts
*cite web
last = Weinheimer
first = Peter
authorlink = [e-mail]
coauthors =
title = Detailed pictures of parts
work = [http://www.radiophil.com/uhren/riefler/riefler.htm Wiederentdeckung und Instandsetzung der Präzisionspendeluhr Riefler Nr. 711 (Rediscovery and repair of Riefler No. 711)]
publisher = radiophil.com
date = 2000
url = http://radiophil.com/uhren/riefler/detailbilder.htm
format =
doi =
accessdate = 2008-05-31
*cite web
title = Clemens Riefler regulator, 1929
work = [http://www.nawcc.org/museum/nwcm/galleries/precision/precision.htm Precision Regulator Clocks Gallery] , National Watch and Clock Museum
publisher = NAWCC (National Association of Watch and Clock Collectors)
date = 2007
url = http://www.nawcc.org/museum/nwcm/galleries/precision/riefler.htm
accessdate = 2008-06-02 Closeups of 3 Riefler clocks and some technical information
*cite web
title = About Us
publisher = [http://www.riefler.de/english/index_e.htm Riefler Industries, GmBH]
date = 2007
url = http://www.riefler.de/english/profil.htm
accessdate = 2008-06-02 Present day Riefler Co., does not make clocks

Footnotes