here are some Delta robot kinematics articles:
http://forums.trossenrobotics.com/tutorials/introduction-129/delta-robot-kinematics-3276/
http://cats-fs.rpi.edu/~wenj/ECSE641S07/delta_calibration.pdf
http://www.eej.ulst.ac.uk/~ian/modules/EEE516/Appendix-%20Riona%20Corrigan%20B0439354-%20Rostock%20Mini%203D%20Printer/Digital%20Appendix/Written%20Report/
http://forums.trossenrobotics.com/tutorials/introduction-129/delta-robot-kinematics-3276/
http://cats-fs.rpi.edu/~wenj/ECSE641S07/delta_calibration.pdf
http://www.eej.ulst.ac.uk/~ian/modules/EEE516/Appendix-%20Riona%20Corrigan%20B0439354-%20Rostock%20Mini%203D%20Printer/Digital%20Appendix/Written%20Report/