Jacopo Aleotti Stefano Caselli Monica Reggiani Evaluation of virtual fixtures for a robot programming by demonstration interface. 536-545 2005 35 IEEE Transactions on Systems, Man, and Cybernetics, Part A 4 http://dx.doi.org/10.1109/TSMCA.2005.850604 db/journals/tsmc/tsmca35.html#AleottiCR05