Picking rates

The throughput of the HTCP system was found to be dependent of a number of parameters. The picking rate of the acoustic dispenser ECHO 550 determines the maximum picking rate that can be achieved. However, with a cycle time of 2 min for each source plate that needs to be accessed, the retrieval of source plates from the store can become a bottleneck. Therefore, the... 

Fig. 5. Dependency of HTCP pick rates on source plate density. The pick rate (number of produced wells per minute) depends on the number of picks that can be taken from the same source plate.

One implementation of bucket brigades reported in [6] was at the national distribution center of Revco in Knoxville, TN. Prior to bucket brigades, Revco faced productivity issues because of its reliance on temporary labor and on overtime during peak periods. Revco used a zonepicking system in which the pick line was partitioned into areas based on the assumption of identical workers but, given their employee experience mix, the actual pick rates of its workers could vary by a factor of three. The result was that the allocations of work were always unequal and the pick lanes were imbalanced the slowest pickers were frustrated at falling behind and the fastest pickers were underutilized. 

The report described in [6] claims that the idea of bucket brigades was explained to the workers in about fifteen minutes one morning. When implemented at Revco s warehouse, bucket brigades reduced work-in-process inventory, which relieved congestion on the conveyor. The reduced congestion and more effective task allocation increased pick rates and accuracy. 

Under the new system, supervisors could monitor the relative progress of different lanes and adjust allocation of workers to keep the lanes coordinated (to reduce sorting downstream). Bucket brigades simplified the shifting of workers from a fast lane to a slow one because there is no need to redefine zones. The research measured a 34% increase in pick rates at Revco when they shifted to a bucket-brigade-based task allocation. 

Weekly average pick rates were measured by Revco over most of a year (normalized to Revcos work standard 1.0). Prior to the introduction of bucket brigades, Revco was picking at about 95% of their own work standard. After bucket brigades, this rose to 134% of their work standard. (p. 3)... 

Storage and retrieval for small lots can be accomplished with mechanized and automated arrangements. Horizontal (Fig. 4.56) and vertical carousels are frequently used, and can achieve picking rates of 100 picks/h. A vertical carousel uses less floor space and resembles a horizontal carousel rotated onto one end. However, the vertical carousel requires an automated retrieval system, since it can reach heights of 35 ft (10.6 m). In either carousel system. 

The system of coupled differential equations that result from a compound reaction mechanism consists of several different (reversible) elementary steps. The kinetics are described by a system of coupled differential equations rather than a single rate law. This system can sometimes be decoupled by assuming that the concentrations of the intennediate species are small and quasi-stationary. The Lindemann mechanism of thermal unimolecular reactions [18,19] affords an instructive example for the application of such approximations. This mechanism is based on the idea that a molecule A has to pick up sufficient energy... 

Diffusion may be defined as the movement of a species due to a concentration gradient, which seeks to maximize entropy by overcoming inhomogeneities within a system. The rate of diffusion of a species, the flux, at a given point in solution is dependent upon the concentration gradient at that particular point and was first described by Pick in 1855, who considered the simple case of linear difflision to a planar surface ... 

The idea may be illustrated by considering first a method for increasing the acceptance rate of moves (but at the expense of trying, and discarding, several other possible moves). Having picked an atom to move, calculate the new trial interaction energy for a range of trial positions t = 1.. . k. Pick the actual attempted move from this set, with a probability proportional to the Boltzmann factor. This biases the move selection. 

Under diffusion controlled conditions tire reaction rate depends, tlien, only on tire supply of 02(g) to the surface which is detennined by Pick s law ... 

The rate of hydrolysis of DMAC is very low, but increases somewhat in the presence of acids or bases. DMAC is a stable compound, but is mildly hygroscopic and desiccation and/or dry nitrogen blanketing of storage vessels are sometimes used to reduce water pick-up. In the absence of water, acids, or bases, DMAC is stable at temperatures up to its hoiling point at atmospheric pressure. Its greater stability enables more economical recovery by distillation relative to that of other similar solvents. 

Steel is an acceptable material of constmction for handling solutions of up to 50% NaOH below 40°C. Above 40°C the steel corrosion rate increases rapidly and iron is picked up in the solution. Materials for handling 50% NaOH are lined steel for tank cars and lined or unlined steel for tanks and piping. 

The rate of mass transfer (qv) depends on the interfacial contact area and on the rate of mass transfer per unit interfacial area, ie, the mass flux. The mass flux very close to the Hquid—Hquid interface is determined by molecular diffusion in accordance with Pick s first law ... 

Results of test work with this filter, producing cakes of 1 mm thickness using a 3 mm clearance, have been pubUshed (33,34). The cake formed on the medium was generally stable, giving high filtration rates over long periods of time, and the precoat type cake did not blind with time. There was no evidence of any size selectivity of the process the only exception was conventional filter aids which were preferentially picked up by the rotating fluid. This... 

Union Carbide has developed Amine Guard, which essentially eliminates corrosion in amine systems (32—35). It permits the use of substantially higher amine concentrations and greater carbon dioxide pick-up rates without corrosive attack. This results in an energy requirement comparable to that of the carbonate process and allows the use of smaller equipment for a specific C02-removal appHcation thereby reducing the capital cost. 

Calcium Oxide. Also called lime or quicklime (4,5), calcium oxide [1305-78-8] (Class 1, nonregenerative), is relatively iaexpensive. It is prepared by roasting calcium carbonate (limestone) and is available ia a soft and a hard form according to the way ia which it was burned. For desiccant service, soft-burned lime should always be used. Calcium oxide is most commonly used to dehydrate Hquids and is most efficient when it can be heated to speed the reaction rate. The reaction product is calcium hydroxide, which cmmbles as it picks up moisture. 

We must also check whether the starting time of the motor with this profile of starting torque would be safe for the motor to pick up to the rated speed. Considering the same data as for Example 7.1, GD = 1866 kgm ... 

Since the motor s fixed parameters can now be varied to suit a particular load requirement, there is no need to pre-match a motor with the load. Now any motor can be set to achieve the required characteristics to match with the load and its process needs. Full-rated torque (TJ at zero speed (during start) should be able to pick up most of the loads smoothly and softly. Where, however, a higher 7 s, than is necessary, a voltage boost can also be provided during a start to meet this requirement. (See also Section 6.16.1 on soft starting.) The application of phasor (vector) control in the speed control of an a.c. motor is shown in a block diagram in Figure 6.12. 

The motor should be mounted with a suitable loading arrangement and the rotor fully locked. The rated voltage at the rated frequency will then be applied to the motor terminals in the locked rotor condition. The loading on the motor will then be reduced slowly so that the motor can start and pick up speed. The value of pull-up torque at which the rotor picks up speed and attains speed corresponding to pull-out torque condition must be noted. 

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