The Stellenbosch University design team felt very strongly about making their UKW gantry robot as energy efficient as possible. Considerable effort was placed in performing an accurate and detailed energy audit. The amortisation period of the regenerative braking unit was also discussed.
The energy saving measures of the project is summarised below:
1. Inherent energy savings from automisation ... Automisation of the process of glass handling could result in an inherent saving of energy due to the reduction of cycle times. Manual glass handling systems require a vacuum generator to be active to manage the float glass production process. This manual process seems to indicate that there may always be the possibility of minor suction leaks in the system. A reduction of cycle times through automisation could save energy by reducing these suction leaks that occur when the suction mechanism is active. Quite simply, by minimising the total production cycle time, this loss of energy is minimised. In addition to this idea, faster cycle times obviously decreases waiting periods for follow-on equipment, thereby reducing non-productive losses associated with standby modes.
2. Reduction of friction … As the main translation axes of the float glass gantry device operates on a guide rail and runner block system, the coefficient of friction is extremely low. This means that irrecoverable energy losses are limited.
3. Suction … Two separate strategies were suggested in order to reduce energy usage when generating suction pressure (focussing on the compressor side):
* Proportional valve control energy saving The use of the proportional valve could allow the magnitude of the suction force to be adjusted to the size of the piece of the glass. Lighter pieces of glass require less suction and therefore require less suction energy. Using the control capabilities of the proportional valve it is possible to decrease suction pressure and energy consumption.
* Vacuum threshold energy saving Initially the design team wanted to suggest the use of the air saving function available on the OVM Festo vacuum generators. However, on further investigation it was discovered that the air saving function was incompatible with the proportional valve control energy savings technique discussed above. It was then decided to recreate this functionality using Festo components.
4. Regenerative braking … A significant quantity of input energy in a float glass system is the dissipated energy of the braking mechanism. This energy could be recovered through the use of the SEW regenerative power supply unit because significant acceleration and deceleration would be expected. During periods of deceleration, instead of losing the energy to ordinary braking (and having to deal with the problem of dissipating energy), the kinetic energy of the load can be recovered, and returned to the supply.
By connecting the DC links of several inverters, the regeneration energy from one axis may be used to power another. This results in a system where the only losses are in the conversion process from electrical to mechanical energy and work done to overcome friction.
5. High efficiency components … The use of high efficiency energy components has the potential to increase energy efficiency drastically.
* Drive Motors The majority of energy supply in a float glass system is consumed by drive motors. Large savings in energy usage can be obtained by fitting energy efficient motors. Servo motors are inherently energy efficient.
* Gearboxes Where possible, SEW Eurodrive helical gears can be selected over worm gears in order to increase gear box efficiency.
* SEW MoviDrives Increases in system efficiency could be obtained by using a high quality frequency invertor such as the SEW MoviDrive.
6. Use of variable drives and intelligent control ... Minimising operational time and “soft start” technologies could further add to the saving of energy in a float glass production system.
* Minimizing operational time Use of an intelligent drive control automatically allows the implementation of advanced energy savings strategies. An example of this is the minimisation of time a particular motor is in operation, by shutting it down during periods of no operation.
* Soft Starting Soft start technologies can be implemented automatically by intelligent drive controllers that reduce the amount of electrical current drawn for mechanical loads during startup.
* Unity Power Factor Motors without a frequency inverter are highly inductive. Driving an inductive load results in more reactive power being drawn, which in turn increases the amount of current being drawn. This increase in current results in higher losses to the internal resistance of the wiring. The use of frequency invertors results in a unity power factor, which decreases reactive power and energy losses associated with drawing current.
For more detailed information about the energy efficiency ideas and products covered in this project, please email us at info@pneudrive.co.za.