NC Reconstruction of High Accuracy Spheres Grinding

The design of NC reconstruction of a machine tool and the parameters conversion are elaborated by means of an example of sphere grinding using a common grinding machine which has been reconstructed by special NC technologies. The grinding of a large size sphere is realized by using the linear instruction. The variable speed rotary grinding of a large size sphere is realized by using the arc instruction. The instantaneous compensation of the grinding wheel is realized by using the screw instruction. The function and application scope of NC technology are expanded because of variable speed rotary motion and instantaneous compensation of the grinding wheel.

Integrating Constructionism and Instructionism in Educational Hypermedia Programs

In many educational hypermedia programs, the original meaning of hypertext influenced the entire pedagogical approach underlying the programs. This meant that learners were free to navigate, construct, and choose their learning path. In addition, no learning objectives were mandatory, and the processes of hypertext navigation and artifact constructions were emphasized. The problem of this trend was that learners received little feedback to guide them on how to use the non-linear structure, and not all could acquire important skills and knowledge of the subject matter. This article deals with an attempt to integrate linear instruction elements into hypermedia programs in order for learners to benefit from the advantages of both approaches. It offers feedback as a connecting unit in such an integration and suggests a model of feedback that fades in and out, based on the fading-out model of scaffolding traditionally used in the apprenticeship approach. A few projects are described to illustrate these ideas.