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Automated Pressure Gauge Filling Station
Final Design Assembly Front View (left) and Back View (Right)
The final product consists of four major parts, the automated oil injection machine, the conveyor system, the integrated PLC control system and the holder.
The Automated Oil Injection Machine:
Injection Module Internal View (left) and External View (right)
Inside the injection module, an acrylic plate separates the enclosure into two parts. A DC power supply and a stepper motor driver is mounted on the top. A level converter is mounted on the other side of the acrylic plate using din rails. The DC power supply powers the stepper motor driver, and the level converter converts 24 Volts square wave signal from the PLC to 5 Volts square wave into the stepper motor driver, which controls the movement of the peristaltic pump. The peristaltic pump is mounted on the bottom side of the assembly using anti-slip nuts to reduce the effect of vibration. Outside of the enclosure, the peristaltic pump is connected with a vinyl tubing, and then a hose fitting and a dispensing needle. The system is sealed using hose clamps and secured using pipe straps. Through theoretical flow analysis, it was proved that the pump could generate enough pressure to push glycerin oils through the tubing system with a safety factor of 23.4, as well as draw oil from the reservoir, which will be placed on the ground.
The Conveyor System:
Conveyor Assembly (left) and Zoomed-in View On Photoelectric Switch
Due to the time constraint, the conveyor system is purchased directly from other manufacturer. The diameter of the base of the pressure gauge holder is 6 inches, while the width of the conveyor is 20 inches. In order to align the gauge holder with the injection needle during transportation, two pieces of guiding rails were installed on the conveyor. The guiding rail is composed by a t-slot and a strand of fishing line, and space for passage for the pressure gauge holder was left between the two guiding rails. During transportation, the holder will be aligned under the constraints of the fishing line. As the holder being transported to the designated location, the laser beam between the transmitter and the receiver will be interrupted. The change in status of the receiver will be perceived by the PLC.
The Integrated Control System:
PLC Circuit Diagram
The control module used here is the Siemens LOGO! 230RCE. The major reasons for using a PLC instead of other controllers such as Arduino or Raspberry Pi are:
PLC controller has better compatibility with most industrial components
PLC controller has better durability compare with Arduino or Raspberry Pi, and it can be replaced or repaired easily with warranty
PLC controller is the industrial standard, as our final product is for industrial application
PLC Control Panel External View (left) and Internal View (right)
It takes power from 115V AC. For safety considerations, two indicator lights, one latching switch, and one emergency stop switch are installed on the front panel. Inside the control panel, there is a circuit breaker, which protects all electrical components from large in-rush current. In Figure 3.4, the first component on the bottom row is a relay, which is a mechanical switch with an electromagnet controlled by input voltage. It is controlled by the CPU, and transmits power for the conveyor. The second component is a power supply that converts 115V AC current to 24V DC current. The third component is Siemens LOGO! 230RCE, which is the CPU of the system and it has relay outputs. The fourth component is Siemens LOGO! DM8 230R, a digital expansion module with relay outputs. The fifth component is Siemens LOGO! AM2, an analog expansion module and is used for galvanic isolation. The last component is Siemens LOGO! DM8 24, a digital expansion module with transistor output of 24V. It can generate high frequency signals itself, and is used to control the peristaltic pump. The Siemens modules were arranged in this specific way so that all voltage levels can be used in this system, which is required to control both the conveyor and the peristaltic pump. There is also an LCD screen installed on the front panel for user input. The LCD screen is connected to the CPU with ethernet cable.
The Holder:
Holder Design Exploded View (left) and Actual Assembly (right)
Due to the geometric constraints of the pressure gauges, it is impossible to directly place them on the conveyor belt . Therefore, it is necessary to design a holder to hold pressure gauges in place during transportation and filling process.
Final Performance Results
At the bottom, a circular base made of aluminum allows the proximity sensor to
detect the holder no matter the orientation of the pressure gauge, which increases the tolerance and accuracy of the alignment with the injection module. Also, the base is designed to have a large weight and size to ensure stability during the movement. Precision shafts are inserted into the counterbored hole on the base and bolted with flat head screws so that the precision shafts would hold still under external load. Last but not least, the center of the funnel is designed to align with the center of the base to ensure the dispensing needle will be aligned with the funnel despite the orientation of the holder.
On the top, placing the plastic funnel between two aluminum plates and bolt them together gives the final model high strength. During the filling process, the pressure gauge is sealed with the funnel, which causes pressure buildup in the pressure gauge and stagnate the flow. Therefore, a two-funnel air discharge system was built to ensure air flow and maintain the pressure as shown. Bolts are also screwed into the top aluminum piece to hold both the precision shaft and the extension spring in place.In the middle, plastic linear bearings and precision shafts are used to reduce the friction of the moving piece on the shaft. Rubbertape is attached on the supporting pin of the holder to provide extra friction to hold the gauge in position. Two extension springs are connected between the pillow block and the 4-40 bolts, providing a holding force for the pressure
gauge, which is supported by the two pins in the front.
Holder Working With Different Pressure Gauges
Automated Filling with PR25
Automated Filling with PR35
Testing Results for Different Pressure Gauges
The system is very accurate in terms of positioning and filling. The positioning of the system is usually within 5 mm, which is less than half of the radius of the funnel, ensuring accurate injection. The filling controlled by the PLC is also very accurate, with error usually less than 1%. The main shortcoming of this system is the speed of filling, with the largest pressure gauge requiring 20 minutes of filling. The filling speed is limited both by the funnel in the holder and the operating frequency of the PLC module.
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