Introduction
We have developed a low-cost stopcock valve actuator for radiochemistry automation built using a stepper motor and an Arduino, an open-source single-board microcontroller. The con-troller hardware can be programmed to run by serial communication or via two 5–24 V digital lines for simple integration into any automation control system. This valve actuator allows for automated use of a single, disposable stopcock, providing a number of advantages over stopcock manifold systems available on many commercial radiochemistry rigs or over using solenoid valves. This actuator allows for the use a wide variety of stopcocks, ranging in size, shape and material, giving flexibility to be used in a large variety of applications.
Material and Methods
The actuated valve consists of two main parts, the actuator and the control electronics. The actuator consists of a stepper motor, an infrared ‘home position’ sensor, a stopcock backplate, and a coupler from the driveshaft to stopcock handle. The stepper motor is a NEMA-17 size that runs 200 steps/rotation with a 5mm drive shaft. The coupler is an interchangeable part, custom to each stopcock model, with each part drilled out to fit the motor drive shaft and milled out for a tight fit to the stopcock handle. The backplane consists of a plate offset from the motor body with 5 screws positioned to keep the stopcock body from rotating relative to the motor. A reflective optical sensor (Vishay TCRT1000) is used as a limit switch to determine a ‘home’ position for the stopcock. With a slight modification to most any stopcock in cutting off a tab that limits rotation, the handle can rotate 360°. This allows for opening all three ports to each other, which has been done to all stopcocks used with this actuator.
The control electronics consist of an Arduino Uno board and a motor shield (add-on board), connecting to the actuator by an Ethernet cable. The motor shield functions to interface the low-power Arduino circuitry with a high power H-bridge motor driver circuit. The Arduino runs two sets of code, initialization and its loop. The initialization routine runs when power is first powered up, and then continues to run the loop. The initialization routine rotates the valve until the IR limit switch is activated, and rotates an-other 45° from position home, sealing off all ports on the stopcock. Following initialization, the Arduino enters its loop, which repeatedly compares its current position to its target posi-tion. When the target position and current posi-tion do not match, the stepper motor turns in the shortest direction towards its target position. The hardware can be interfaced by either serial communication or by two 5–24V digital signals defining positions 1–4. The wide range of allowed input signal voltages is realized by using an optocoupler that accepts 5–24 V inputs but outputs TTL signals compatible with the Arduino’s hardware.
Results and Conclusion
A photo of the implementation of the actuator is shown in FIGURE 1. It has overall dimensions of 3.5×1.75×2.5”, excluding a mounting bracket. Control electronics are housed in a compact box built for an Arduino, giving the control electron-ics a clean, professional look. Challenges in de-sign included determining a maximum motor speed where the motor would provide enough torque but yet move fast enough to be useful, finding that rotational speed of 6 seconds/full rotation is best.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:22284 |
| Date | January 2015 |
| Creators | Vandehey, N. T., O\'Neil, J. P. |
| Contributors | Lawrence Berkeley National Laboratory, USA |
| Publisher | Helmholtz-Zentrum Dresden - Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:conferenceObject, info:eu-repo/semantics/conferenceObject, doc-type:Text |
| Source | WTTC15 |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | urn:nbn:de:bsz:d120-qucosa-162048, qucosa:22221 |
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