Eray Cavus 030060022 9th Week 2th part

Synthetic Adhesives (Chemical Adhesive)

Synthetic Adhesives (old)

A simple classification is depicted in Figure 4.1. Adhesives are either produced from a natural source such as starch glue or as is the case with the majority of consumptions, they are synthesized from basic hydrocarbons. The synthetic group consists of thermoplastic and thermosetting adhesives, both of wich follow the definitions used in plastics for thermoplastic and thermosetting polymers.

Synthetic adhesives term is usually used to apply to all adhesives other than natural adhesives (i.e., elastomeric, thermoplasitc, thermosetting, and alloys). All structural adhesives are synthetic.
(Sina Ebnesajjad, Adhesives Technology Handbook, p.49-50)

Synthetic Adhesives (new) (better)

Synthetic adhesives are just that- they are chemically synthesized adhesive agents, not just synthesized systems containing natural adhesive agents! By this definition, alla re polymeric materials, and subclasses include thermosetting polymers, thermoplastic polymers (including elastomeric types), and combinations or “alloys”of these subclasses. All structural adhesives except cements and mortars (which, while based on naturally occuring materials, are actually carefully formulated and processed!) are synthetic.

(Joining Of Materials And Structures, Yazar: Robert W. Messler, page:232)

Incremental shaft encoder (Angular Digital Encoder)

Incremental shaft encoder (old)

The term of shaft encoders is used for a device which gives an output in digital form related to the angular position of a shaft. The incremental shaft encoder gives just on-off signals as the shaft rotates and the angular position af the shaft can only be determined by couting the number of these pulses that has occured since the shaft was at some particular position. Figure 3.30 shows the form of a simple incremental shaft encoder. it consisit of a disc which rotates along with the shaft. the form of the disc depends on the transducer used with it. In the optical form the disc has a series of windows through which a beam of light can pass. The beam of light falls on a light-sensitive transducers which gives an electrical output. Rotational of the shaft means that the light beam is pulsed and so the electrical output from the transducer is a series of pulses. These can be counted and so the angular position of the shaft determined by the number of pulses produced since some datum position. Where the rate of rotation of the shaft is required then the number of pulses produced per second is determined. (Industrial control and Instrumentation-W. Bolton-page 65)

Incremental shaft encoder (new) (better)

An incremental encoder disc uses a single track, usually with optical detectors to provide sine and cosine outputs, similar to the resolver output described above. In addition, a single mark on the disc with an associated optical pick-up is used as an angular datum from which the actual angular position of the shaft can be determined. One of the outputs of the sine/cosine pair is used to count the number of bits to or from  the datum. Together the sine/cosine pair are used to determine the direction of rotation(Woolvet 1977) and hence an up or down count of the counter.

The current counter output represents the absolute value of the angular position of the shaft from datum. When starting, the encoder disc must pass the datum position before the digital output has any validity. The two seperate outputs, sine/cosine, also provide opportun,ty for increasing the resolution, either by interpolation as described above or by similar techniques. The simplest method is to use the leading and trailing edges of both outputs to develop a count pulse, thus increasing the resolution by a factor of 4. A disc with 5000 segments, which is about the maximum currently available, on a disc 150 mm in diameter, can, therefore, provide 20000 pulses in one revolution without any revolver techniques, which represents a resolution of approximately 1 minute of arc. In incremental encoders as in any other position encoder using counting and/or triggering circuits, there are limitations on the speed of rotation due to the maximum switching speeds of the electronics. However, for rotational speeds found in industrial situations, suitable electronics is available.

(Instrumentation: A Reader, Yazar: R. Loxton,P. Pope, page:27)