Makerbot

http://www.makerbot.com/blog/2013/02/22/replicator-2-extruder-alternative-some-spring-in-your-step/

http://traverseda.wordpress.com/2014/05/23/makerbot-blatently-steals-and-patents-a-community-design/

http://www.makerbot.com/legal/patents/

https://www.google.com/search?tbm=pts&hl=en&q=makerbot

Quick release extruder
http://www.thingiverse.com/thing:7129

http://www.freepatentsonline.com/y2014/0120196.html

https://plus.google.com/+jwildeboer/posts/hsQRqmWXD4y

http://www.makerbot.com/blog/2013/02/22/replicator-2-extruder-alternative-some-spring-in-your-step/

http://web.archive.org/web/*/http://www.makerbot.com/blog/2013/02/22/replicator-2-extruder-alternative-some-spring-in-your-step/