Figure 1. The Sandbags Super 50 can produce up to 2,000 sandbags/hr, giving local agencies the ability to respond quickly in emergency situations in order to protect property and save lives.
During natural disasters, sandbags are used to protect people and property. In addition to becoming lifesaving tools during floods and storms, sandbags are also used to provide a steady base for oil, gas, and water pipelines. Sandbags are used in these situations because they provide consistent, flexible weight that enables them to become effective barriers and ballast in a variety of applications.
Sandbags and Dynapac Design Group, a machine builder OEM headquartered in Carlsbad, California, enlisted the aid of InduSoft and its value-added reseller Quantum Automation to improve the monitoring capabilities and control of their sandbagging machines (Figure 1).
For this process, operators load sand into a hopper on the Sandbags Super 50 trailer (Figure 2). A sand delivery conveyor belt feeds equal amounts of sand into a loading spout on which an empty sandbag is attached. Using a proprietary measuring system, an accurate volume of sand is delivered and is then discharged into the sandbag.
Figure 2. The Sandbags Super 50 Machine is a mobile operation made more efficient by connectivity to the central operations center.
Each sandbag is dropped onto a conveyor, sewn closed as it moves along the belt and raised to a greater height. A third conveyor then loads the sandbags into a large supersack with the guidance of an operator. One or more supersacks are then loaded onto a flatbed truck to be delivered to the sites that need the sandbags.
A complete factory on wheels
Investigating the Sandbags Super 50 at a more granular level reveals the many pieces that make the system a complete factory on wheels. All components have been chosen not only for functionality, but for their ability to reliably perform over the long haul in highly abrasive conditions in outdoor environments. The entire assembly rides on a heavy-duty trailer so it can be transported as needed.
Operating personnel perform some manual actions, but the process is mostly automated, boosting overall productivity to more than 2,000 bags/hr. An infeed hopper must be replenished by operators using a skip loader or other similar equipment, with the hopper’s 4.5 cubic yard capacity minimizing the number of required refills.
There are two identical and parallel filling systems served by the in-feed hopper. On each line, a constant-speed sand conveyor belt is operated by a 7.5 hp hydraulic pump to deliver sand into a bag-dispensing hopper. Hydraulics were chosen as most suitable for this service due to the heavy load and frequent start/stop duty cycle of once per second.
A volumetric measuring system is used instead of a weighing system due to its superior reliability and reduced maintenance requirements. The resulting accuracy is more than enough for the application as bags are filled at ±1 lb, or 2% of a standard 50-lb sandbag. Operators must perform a basic column calibration procedure at the beginning of each day to account for local sand density, and this brief operation fine-tunes the sand conveyor belt start/stop cycles to optimally fill the hopper spout.
A proximity sensor detects when the operator has positioned an empty bag on the hopper spout, at which time the bag is filled automatically and then dropped onto the production conveyor belt for transport to the sewing station. After the manual sewing operation is completed, an incline conveyor takes the sandbag to a reversible shuttle conveyor which is used to fill supersacks with sandbags. Supersacks vary in size and can generally accommodate anywhere from 25 to 200 bags, with operators selecting the appropriate size and corresponding number of sandbags.
All conveyors are driven by variable frequency drives (VFDs) and gear motors. This allows speed differentials to be set as needed to separate the bags for the final loading operation and also provides a ramped starting and stopping action. The two lines use a total of six conveyors.
Two PLCs provide the brains of the operation. PLC1 provides supervisory real-time control to monitor sensors and operate sandbagging conveyors. PLC2 performs data acquisition, as well as control of auxiliary systems including an air compressor. PLC2 also controls, collects data from, and monitors the system for a self-contained onboard diesel generator which powers the machine.
Most control system input/output (I/O) signals are discrete (on/off), although some analog input signals are used to monitor pressures, temperatures, voltages, and environmental conditions. In addition to equipment control signals, discrete inputs monitor buttons and switches, and discrete outputs drive signal lights. The system is designed so no analog closed-loop control is needed, simplifying operation and maintenance and reducing interference issues with static and electrical noise.
This factory on wheels was designed from the sand up to reliably fill sandbags at the greatest possible rate, overcoming design obstacles along the way.
Extensive communications pose challenges