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Servo Feedback Devices and Motor Sensors
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
If the selection is limited to encoders, the first decision to be made is to select either incremental or absolute encoders. As mentioned previously, an absolute encoder provides a snapshot reading of the rotating angle and speed of the motor shaft and therefore determines the absolute position. By contrast, an incremental encoder indicates the relative position and direction of movement by adding incremental pulses to a known start position. It is ideal for speed control of motors since it provides a real-time reading of the shaft position and keeps track of absolute position by counting the number of pulses per revolution (PPR). However, this position count could be lost during a power failure or system shutdown. In such a case, it may be necessary to return the machinery to a known reference position and restart the position count before operations can resume [8.94]. For better understanding of the difference between the two types of encoders, consider the difference between a stopwatch and a clock. A stopwatch measures the relative time that elapses between its start and stop points. This is similar to an incremental encoder to measure the relative shaft position from the specified point. A clock, on the other hand, shows the exact current time within a day, similar to an absolute encoder to measure the absolute position of the shaft.
Time Study
Published in Stephan Konz, Steven Johnson, Work Design, 2018
There are two types of stopwatches: mechanical and electronic. First, assume that the watch is used in the snapback mode (at the end of an element, the timing starts from zero). The mechanical watch has been available for many years and is still used occasionally. Much more common now is the electronic watch. The electronic watch has three advantages. First, it has a digital display instead of an analog display so it is easier to read. Second, on a mechanical watch, when an element ends and the watch starts at zero, it takes a small amount of time to move the hand to zero (workers don’t like to have this time omitted). On an electronic watch, there is no time required to move the hand. Third, on an electronic watch, the time at the end of an element can be “frozen” so the analyst observes a fixed display while the timing continues. On a mechanical watch, the analyst must remember where the hand was before it was reset to zero.
Standardized Work Chart: Building on an Idea
Published in Timothy D. Martin, Jeffrey T. Bell, Scott A. Martin, The Standardized Work Field Guide, 2017
Timothy D. Martin, Jeffrey T. Bell, Scott A. Martin
When we are ready to stop timing the observation, we must align our stopping point to ensure that the last cycle captured is complete. In most cases, this means that worker may have to walk back from the last station in the process to return to the first station and then reach the point that would signify the beginning of the next cycle. Once this start/stop read point is reached, the timing on the stopwatch is stopped by pressing the appropriate button on your model of stopwatch.
Optimization of an angle between the deflector plates and its orientation to enhance the energy efficiency of Savonius hydrokinetic turbine for dual rotor configuration
Published in International Journal of Green Energy, 2022
Figure 4 indicates the photograph of the experimental setup used for the present experimental analysis. The design parameters used for the rotor are shown in Table 2, and the detailed nomenclatures used in the rotor design are shown in Figure 5. The torque on the turbine shaft is applied by winding the cord on the turbine shaft. The tension on the cord has been altered using different loads on the end of the cord. The tension is measured using load cells attached at both ends of the cord. The torque is calculated using applied tensions on the cord and measured shaft radius. The turbine rotor’s angular velocity is calculated by measuring the time for 15 revolutions of the turbine shaft. The time is measured using a stopwatch with an accuracy of 0.01 s. The experiments are extended to turbine rotor stops by gradually applied to the load. The obtained values of torque, power output from the turbine, and angular velocity of the rotor are presented as the coefficient of torque (Ct), co-efficient of power (Cp), and Tip Speed Ratio (TSR), respectively. The results obtained from the experimental analysis are shown in Figure 7. The maximum coefficient of power of 0.112 at a tip speed ratio of 0.55 is recorded from the experiments.
Machining performance of high energy die-sinking electrical discharge machining on GH2132
Published in Materials and Manufacturing Processes, 2020
Ming Li, Zhuojun Yang, Hang Dong, Yu Zhou, Yonghong Liu
During each experiment, a stopwatch with an accuracy of 0.1 s is used to record the machining time. The weight of both workpiece and tool electrode before and after machining are acquired by a balance with an accuracy of 0.1 mg, respectively. MRR and REWR are calculated by equations (1) and (2) based on the above data. After each machining, a vernier caliper with an accuracy of 0.02 mm is used to measure outside diameter of sample. Each sample is measured four times at four locations with a uniform distribution of π/4 radians. The average value of four measurements is used to acquire DOC by equation (3). To increase the reliability of results, each group of experiment is repeated three times.