Feature Drives & Controls
An energy saving solution for machine builders
Machine builders are increasingly under pressure to build energy saving features into their industrial machines. Andrew Davies, an expert in machine building at Bosch Rexroth, argues that capacitance modules could offer a simple solution
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scalating energy prices has led to energy saving becoming a higher priority for machine builders, as there is more and more pressure for energy saving options to be fitted to industrial machinery in order to help mitigate the impact of rising prices for end users.
One method of achieving this is to use simple capacitance modules which can improve the energy bal- ance in applications where machin- ing cycles take place in rapid succession, for example, roll feeds or cross cutting lines. Effectively, the capacitance module acts like a kinetic energy recovery system (KERS) on a Formula One car, which has become very popular in F1 in recent seasons. The KERS system recovers a moving vehicle’s kinetic energy under brak- ing, which is then stored in a reser-
voir, such as a flywheel or a battery for later use under acceleration. With a capacitance module, which is connected to the DC bus, the machine effectively has a temporary energy storage unit which can reduce the heat loss in the control cabinet by relieving the braking resistor.
A key role to play
The primary role of the capacitance module is, in the event of a power failure, that the reserve energy enables a controlled retraction motion. This protects the workpiece and the tool, for example in gear cut- ting machines. Rather than use the energy generated by braking to pro- duce heat in a braking resistor, the energy is stored in a capacitance module and re-used on the next cycle of the machine. However, an additional benefit of
the capacitance module is that in storing energy, the panel does not become overheated and there is no need for a cooling system to keep the panel cool.
In recent years, Bosch Rexroth has worked extensively with Henrob, the global manufacturers of self piercing riveting equipment, to introduce capacitance modules into a number of the company’s machines.
This has enabled both parties to analyse the impact of capacitance mod- ules in actual production environments.
Savings outlined
Figure 1 (below left) is a breakdown of costs using 500 capacitance mod- ules on a vehicle production line, which requires the driven load to stop very quickly. As illustrated, 1.3A of energy is used during an average cycle with 400V input into the machine, and each rivet taking 1.6 seconds. With a capacitance module in use this results in a 13.36% saving in current.
During the course of a typical pro- duction day, 500 cars will be manufac- tured, each with 3,000 rivets, which equates to 1,500,000 rivets per day with a total kWh of energy per day of 14,056.25 costing £1,686.75. The saving from the capacitance module equates to £225 per day which over a 12 month period, resulted in a saving of more than £54,000. Ultimately, the use of a capacitance module in this automo- tive application had a payback period of 2.64 years.
Therefore, it is clear that capaci- tance modules can play a significant role in helping to save energy and cut costs in machinery applications. Crucially, capacitance modules have a relatively low unit price and can there- fore, offer a short payback period on any investment.
Bosch Rexroth
www.boschrexroth.co.uk T: 01480 223 200
Automation FEBRUARY 2013 Enter 212 17 Above: using
simple capacitance modules can
mitigate the impact of rising energy costs of industrial machinery
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