Building a Smarter Warehouse

February 6, 2012

Back to the Table of Contents | Vol. 2 No. 5

The material handling industry is finding an increasing amount of technologies applicable to creating a more useful, efficient warehouse environment. Automatic warehouses save energy in many ways; from efficient, lighter engines in the AS/RS systems, intelligent motion calculations and regenerative power supplies to the simplest of all energy savings method: turning off the lights.

The Healing Power of Regenerative Braking
The principles of physics assert that energy is neither created nor destroyed – it is transformed. When an automated machine is in motion, the kinetic energy created from this movement must go somewhere when the machine slows down. When a stacker crane stops, its kinetic energy is turned into heat. In a non-regenerative braking system, that heat dissipates and is lost. Regenerative braking – a still infant technology only recently being absorbed by the material handling industry – recaptures this energy and uses it to power up other machines within the same warehouse. When an electrical motor, like the types propelling AS/RS, runs in a single direction, it converts electrical energy into mechanical energy that can be used to perform the necessary functions of that machine (such as extending down narrow aisles or reaching the top level of high height shelves).

Regenerative braking systems engineer the motor to operate in both a forward motion and then switching to a reverse, effectively creating heat similar to that of the child’s prank known as a “mercy burn,” in which one person holds another’s forearm firmly in both hands, and then twists in opposite directions, creating heat friction on the arm. With AS/RS units, this forward, then backward motion allows the motor to also switch from an electricity converter to an electricity generator by redirecting the mechanical energy back into electricity. In order for the motor to reverse rotation and generate electricity, the vehicle’s momentum must be the mechanical energy used to throw the motor in reverse.

This is trickier in AS/RS systems than within motor vehicles, as the start and stop times for an AS/RS unit are extremely brief as compared to the coasting time of a car on a highway. Still, the energy necessary to power an AS/RS unit is much lower than a car. What results from harnessing each little flush of heat given off by an AS/RS brake is a partially self-sustaining system that uses the machine’s momentum to create energy, which is then fed back into the system to charge the motor without having to borrow as heavily from an outside power source.

Control Software, Control Energy
Regenerative braking doesn’t just conserve energy in a single automated unit either. If organized properly in a fully functional automated cold storage warehouse, the heat given off in the automated units would normally destabilize the temperature in a freezer space, which would, in turn, cost more money to restabilize. Regenerative braking also conserves energy across multiple units. Facilities with more than one stacker crane use the energy generated by one machine to power the others. The energy recuperated returns to the plant grid and it is used to power lights, heat and cooling systems and to operate the stacker cranes. Control software, such as the Mecalux Group’s Galileo, enables the system to organize the stacker crane’s motions. This times and coordinates the ascent and descent of the crane, making it use the least amount of energy, and the descent of one machine powers the ascent or startup of another.

In a big installation with several machines, Galileo ensures that each stacker crane starts at a different time than the other stacker cranes. Mecalux’s Hayat installation in Turkey is a good example of how this system works. With the warehouse’s total elevation near 140 feet, its stacker cranes move two pallets at the same time, so they carry large amounts of weight. The energy needed to move these heavy loads so high can be costly. Mecalux found a way to maximize the efficiency of the installation. “Regeneration in these circumstances is very advantageous because what goes up must come down,” Luis Escobedo, robotics innovation director for Mecalux Spain said, “and everything that goes down regenerates a percentage of energy. If the expense of going up is 100 percent and we regenerate 60 percent going down, it only cost us 40 percent to go up and down.”

The Mecalux Group’s software also sets a control system that continuously calculates the time required for each machine to get to any position. To save the most amount of energy possible, the software tries to make one crane’s descent coincide with the acceleration of another, ultimately reducing consumption. Starting a machine is the most costly expulsion of energy a stacker crane performs. Galileo software anticipates when each of the 15 cranes in the Hayat installation need to move, starts them individually and utilizes the power generated by one to assist the next; continuing through the cycle of 15 and repeating. Firing up all 15 machines at once would almost require the warehouse to have its own nuclear plant.

Heavy Metal
Due to the height of the Hayat installation, and the weight of the loads transported, the size of the crane’s engines was maximized to increase their efficiency. Mecalux wanted the motors to be big; the bigger the motor the higher efficiency that can be achieved. They generate more energy and are able to save more energy as well, making up for the higher sticker price, which is usually 5 to 15 percent higher than regular engines.

Another way to save energy is to remove weight from the engine instead of installing a larger one to the AS/RS. Escobedo explained that reducing the weight of the stacker cranes from 31 tons to 26, required less energy for the motor to start. Starting the machine uses more energy than moving it once it is running “When the motor starts, it spends 75 kW, as much as approximately 90 microwaves working at full power. Once the machine is running, it only needs 2 kW, the equivalent of just three microwaves working at full power.”

Light Saver
Escobedo added that innovative engineering isn’t always necessary to conserve hefty amounts of energy in a warehouse. “If you want to reduce your energy bill, turn off the lights.” Darkening warehouse space is probably the easiest, most efficient way to save money and energy in an automated warehouse. In a conventional warehouse, personnel with forklifts pick the pallets from the shelves, so the area needs to be illuminated. When the warehouse is 50 feet high and the lights are on the ceiling, very powerful lamps are needed to illuminate the area, roughly 700 watts per 107 square feet. In a fully automated warehouse, no light is needed, since the stacker cranes can function without it. There is usually an emergency light; though, it is rarely on. This adjustment alone can make the biggest impact in the client’s electric bill.

In the case of lighting, the introduction of LED lamps for industrial settings has further led to increased savings, since LEDs consume about a third of the energy of regular lights. These lamps also have a quick start, as compared to their incandescent counterparts, which can take up to seven minutes to fully illuminate.

Smarter machines, integrative software, lighter motors and advanced lighting are several of the ways an automated warehouses conserve energy, money and the environment while enhancing the productivity of storage spaces. Mecalux is constantly improving its software package, motors and machinery design to meet the demands of its clients and maximize the effectiveness of its machines.