Energy-saving robots - How do you make a robotic production line save energy?

The end of the year?is a time of increased activity in production plants, logistics centres and warehouses. Speed is of the essence, as it enables more goods to be delivered on time to customers, thereby increasing revenues. The use of industrial robots helps to achieve this goal. However, using them on a large scale involves increased energy consumption, which, with rising prices, can be quite a challenge and financial burden for businesses. So how do you find a compromise between the high performance of a robotised production line and saving energy? Here are some tips.

Precisely select robots to meet the needs of your plant

The primary criterion for choosing a robot should be how suitable it is for the tasks assigned to it. In this context, two parameters count above all: payload and reach. For the production manager, these are much more important indicators than energy consumption. However, the right selection of a robot's payload and reach for its function can also result in saving energy. There can be a temptation among managers to choose robots with extra-high payload, extra high performance, or simply large robots, for the plants they manage. Such an approach gives a false sense that the robot will not fail under any conditions. However, this can mean higher energy bills. This is why, before buying a robot, it is important to precisely define your needs and match them to a specific solution and model.

Light robots consume considerably less energy, so it makes sense to use them for tasks that involve handling light loads. If the workload of the robots in your facility varies, it is a good idea to purchase different types of robots, so that occasional tasks that require robots with higher payloads and reach can also be handled. The energy bill will then remain at an optimum level.

Optimise the robot's working environment

If the decision at the factory has already been made to choose a particular robot or fleet of robots, we can handle the reduction of energy consumption by arranging the environment in which they are to work. In the case of stationary robots, the solution may be to design the cell in such a way that the robot arm movements are as short as possible. Placing robots in semi-open halls is another way to generate energy savings by specifically designing the space for these machines. We are seeing a growing interest in robots that can operate at very low temperatures, close to zero. These include, for example, pallet-compacting robots that do not require constant human presence. The spaces in which such robots operate (semi-open halls) are not heated, which allows considerable energy savings.

Minimise energy loss with robots of innovative design

The energy efficiency of robots has so far not been particularly emphasised by the manufacturers of these devices. However, there are some more or less innovative solutions on the market that guarantee greater energy savings than others. These are worth seeking out. One example is the CP series from Kawasaki Robotics with the E03 controller. These are robots that handle quite large loads, such as bags, in the palletising process. These robots use a mechanism that allows energy to be recovered when the arm loses speed. When the gripper stops at the point where the load is to be deposited, the robot uses motors for braking. In traditional solutions, the energy generated then is transferred to resistors and is released as heat. In new designs, such as CP robots, this energy is recovered and sent back to the grid. The CP series robots have lifting capacities of 180, 300, 500 and even 700 kilograms. The heavier the goods they carry, the more energy savings the new system generates.

Innovative robot designs for lower energy consumption are also those that are not directly inspired by the structure of the human musculoskeletal system. Traditionally, robots are equipped with six-axis arms, modelled on the human arm. With a slightly more precise description, they can be distinguished by the equivalent of an arm, forearm, wrist and fingers in the form of a gripper. Such a design is very intuitive and functional. It is easy for a human to programme such a robot, as he or she can easily imagine how the gripper should position itself to grasp a particular object. However, it is not always an optimal design from an energy point of view, as a large number of moving parts means a large number of servo motors consuming electricity. Reducing their number saves energy not only because there are fewer active motors, but also because, with fewer of them, the whole device is lighter. Robots in which traditional grippers are replaced by electromagnetic grippers that stick to the surface of the objects to be handled are an example of such a departure from solutions inspired by the human body. Many types of robots traditionally use cast-iron construction, which guarantees long life. However, when the robot is not intended for heavy-duty use, a lighter construction, such as a combination of steel and plastic, may be chosen. Following this logic, Kawasaki Robotics has developed delta robots with a very lightweight construction. They are used to handle very small workpieces, up to three kilograms, at very high speeds. In their case, energy consumption is relatively low due to the low weight of the robot itself and the goods being moved.

Monitor energy consumption

Sometimes the cause of a robot's increased energy consumption can be a failure of its components. A way to check that this has not happened is to use special software to monitor energy consumption. The software verifies how much power is consumed by the individual axes of the robot and, when energy consumption is significantly higher, signals the possibility of overload or damage. Increased power consumption of individual parts of the robot could, for example, be the result of a damaged gearbox that generates high loads. The software can detect this cause and, through service intervention, restore the correct energy consumption. The plant owner or manager can monitor the robots' energy consumption themselves, or outsource this to the company that was responsible for the robot implementation in their organisation. There is also software that makes it possible to monitor not only individual robots, but entire robotised production lines and to verify energy consumption costs in real time. It works, for example, by detecting the risk of exceeding the declared level of power consumption, thus the risk of paying a penalty, and then temporarily switches off robots that are idle at the time of the peak.

Set robot operating hours intelligently

Prudently setting the operating hours of a robot line is yet another way to save on energy. A production manager wishing to address this issue should review the detailed assumptions of the plant's energy tariff and, if its characteristics allow it, move the greatest robot activity to the ‘off-peak’ nighttime hours. To get the timing of the robots right, the very application that controls them should be written so that individual machines are switched off when they are not in use. A robot that is on standby/resting is still drawing energy. Its motors are on and these are what keep the robot arm stationary. They make the torque on the selected axes be applied in such a way that the arm remains stationary. However, the power to the motors can be switched off and the mechanical brakes activated. Then the individual axes do not consume energy and the total energy consumption decreases. It is also worth bearing in mind that robots are good for repetitive tasks, as setting them up and programming them takes time. Therefore, when a production line often needs to be rebuilt, it is worth considering whether to at least partially delegate the tasks performed by robots to humans and temporarily switch off the robots themselves, thus reducing energy consumption.

Check virtually before you apply

Sometimes it is difficult to determine whether and to what extent modifications to a robotic line will contribute to energy savings. In such a situation, the solution may be to create a virtual copy of the line - a so-called 'digital twin'. In this way, various scenarios can be tested in a virtual environment: changing the order of robots on the production line, modifying the weight of loads carried by each machine, changing parameters such as payload, reach, testing scenarios in which groups of robots are switched on and off, testing work at different times. Once such tests have been carried out, it will be easier to make decisions on the performance of the robots in the actual plant, which will translate into various benefits, including energy savings.

Don't overspeed

There is another factor to keep in mind when thinking about reducing the energy consumption of a robotic line - the speed, or more precisely the acceleration and deceleration of the arm of each machine. Indeed, it turns out that reducing the acceleration and deceleration of industrial robot arms can reduce energy consumption by up to 40%. At least, this is what a study conducted by Chalmers University of Technology in G?teborg shows. It may seem that a robot's rapid movements allow it to more easily reach demanding production targets, but this is not the case at all. Robots that accelerate and brake more smoothly, researchers prove, are just as efficient in the long term as those that move very briskly. So, if the robot's application allows it, it is worth ensuring that the speed of each machine is calibrated to be as energy efficient as possible. It is also worth ensuring that machines working in the same robotic line are well synchronised, so that situations in which one robot moves rapidly while another waits (which also involves energy consumption) are rare. In the face of the energy crisis, more and more entrepreneurs and managers of production facilities and logistics centres are starting to think about saving energy. This is a rational approach in difficult times, but the benefits can be spread over years, even when the crisis is over. Importantly, this will not only reflect on the health of company budgets, but will also have a positive impact on the environment. An energy-efficient robotic production or logistics line is therefore an investment that is sure to pay off.

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Author of article: Wojciech Trojniar, Robotics manager at ASTOR