KEBA robot control KeMotion with its built-in feature «Intelligent Motion» ensures a long look-ahead path and motion planning.
Robot-based pick & place applications are booming with no end in sight. Compared to fixed machine concepts, mechanical engineer companies appreciate the improved flexibility and increase in performance. Using robots means a higher degree of automation, resulting longterm in a reduction of manufacturing costs and, at the same time, an increase in productivity.So what are the challenges facing suppliers of control systems and how has the Austrian automation specialist optimised its robotic solution KeMotion Packaging in this respect?
The starting point in the packaging industry
Automated pick & place is usually associated with increased productivity. The benchmark here is the number of products that can be placed successfully in a target position per minute. In order to obtain the best possible results you require exact programming with look-ahead tracking.Productivity decreases as soon as the robot has to wait and is thus at a standstill. This may be the case, for example, if the product flow on the conveyor belt is interrupted and there is no product to be picked up in the robot’s workspace. The robot may also have to wait, however, when placing the product, until a tray has reached an appropriate position on the conveyor belt beneath it. In this case it can happen that the robot is inactive for some seconds.Such problems are caused by a lack of path planning. As a rule, PLC/motion-based systems can calculate only one individual motion segment in advance. This means that the planning scope is limited as a result, valuable time is lost through inactivity and productivity suffers.Similar idle time together with reduced productivity can be observed when robots use the same working space. Regardless of the fact that you require an elaborate locking system for the workspace, the robots are forced into inactivity again and again as they approach the shared area because there are times when this workspace is occupied by another robot.
Familiar problems of conventional control systems
«Stop & go» operation: this refers to abrupt braking followed by fast acceleration of the robot. Besides the increased energy consumption due to the numerous braking and acceleration processes, this also puts pressure on the robot’s mechanical elements. The risk of plant stoppage increases with these additional vibrations. The effects of stop & go operation thus also include shorter maintenance intervals and in the worst case even the limitation of maximum robot speeds and accelerations which in turn reduces productivity even further.
Time loss: idle time is anathema to productivity, especially in the caseof robots. Constant «stop & go» has a negative impact on pick & place performance. To continue with the planned track the robot always has to accelerate out of inactivity, which costs valuable time and energy.
Limited workspace: a lack of lookahead path planning forces the user to configure the robot’s workspace according to the worst case. This can result in the workspace in use being only half of what is theoretically available. This is caused by the fact that the robot cannot approach the object that is to be picked up until it enters the workspace. As a result of the reduced workspace the number of products on the conveyor belt is lower and the buffer volume is restricted. The robot can no longer compensate for any fluctuations in product flow. In some applications this requires the use of additional robots to achieve the desired pick performance.
Help from KeMotion thanks to «Intelligent Motion» look-ahead path planning
The control specialist KEBA has taken on precisely these challenges and added the option «Intelligent Motion» to the established KeMotion Packaging system solution for packaging robots.
This now enables foreign objects to be included in the path planning as well. These may include, for example, other robots and moving products on a conveyor belt. Look-ahead path planning enables the control system to react to upcoming events in good time and automatically use the most intelligent strategy in the sense of increasing productivity without the need for any additional programming activity.
Benefits through innovative combination of robot control and PLC
KeMotion combines high-performance robot control with a freely programmable PLC on a joint hardware platform. Cyclic process management and the control of peripheral equipment are handled in the CoDeSys-based PLC environment. The event-based robot system, on the other hand, is responsible for the entire motion planning, taking into account maximum dynamics. This unique combination enables both technologies to be used simultaneously with an optimum approach to the respective application.
KeMotion controls up to 64 servo axes. A maximum of 8 robots can be run with a single control system.The user-friendly KEBA robot programming language KAIRO is used in the robotics section. The easy set of commands which is typical for robot programming stands out through selfexplanatory and clear instructions. KAIRO programs can be generated and modified offline on a PC and also directly on the machine. Unlike conventional systems on the market, a typical pick & place program created in KAIRO needs only a few lines. This clear representation makes it easier for the user to generate motion sequences.
Only a good control system knows when the robot will be where
The KAIRO program is interpreted online using the Kemotion control system. Forward-thinking planning also comes into play here. This processes up to 30 KAIRO program lines in advance and determines the motion path to be carried out. This means that the control system can say in advance exactly when a robot will be in what position of the track – seconds before its tool centre point actually passes this position. Besides position, speeds and accelerations are also taken into account. This way, undesired peaks in the dynamic processes of the individual robot axes can be avoided effectively.In order to take into account external events such as defined speed, machine stop, tracking signals etc. the testing and any required correction of the motion path takes place in the interpolation cycle. «Intelligent Motion» enhances this sophisticated track planning even further and also takes into account objects which are foreign to the robot. The key benefit here is that the time pattern of such objects is also integrated in the calculations as a result.
An example taken from everyday life shows the principle quite clearly:
You are in your car and approaching a crossing with traffic lights. The lights are on red and another car is just driving over the crossing. Above the traffic lights there is a display sign that tells you how long the lights will still be onred for you.
Thanks to this information you can now adjust your speed exactly so you do not actually have to stop your car. As you know when you will be allowed to drive over the crossing again you can already start to build up speed even if the lights are still on red for you. This is because you know, of course, when the lights are going to change.
The advantage of this display is that the car does not come to a halt as a result and you can drive over the crossing at the maximum possible speed as soon as the lights change to green again. This means that you reach your destination in the quickest possible way and you also save fuel at the same time.You always have an eye on the time display and the lights, of course, so you are always in a position to brake in an emergency – for example if the other car stops suddenly in the middle of the crossing.
If we transfer this to two robots working in a shared area, this means that one robot tells the other how long it still has to wait in the workspace using look-ahead planning. The second robot automatically optimises its path speed based on this information about time. And if we take it one step further to the pick & place application field it also means that the KeMotion control system knows when a product is going to reach the robot’s workspace. Based on the current position of the robot, its speed towards the product that will enter next can be chosen so that it is picked as early as possible when it actually enters the robot’s workspace. As a result, full advantage is taken of the given workspace and throughput is increased effectively.
Better performance, smoother movements, lower energy consumption
In pick & place applications with unstructured product flow robots are constantly confronted with random idle time. This is ingeniously avoided by the «Intelligent Motion» feature, resulting in a significant increase in performance.
Thanks to look-ahead motion planning and taking into account foreign objects you can gain up to 10% in time through KeMotion alone, without the need for any additional programming.
In addition to this the look-ahead calculation of the robot’s path maximises the robot’s workspace. Products are picked at the earliest possible time. This way the robot can efficiently compensate for any fluctuations in product flow as it can access the conveyor belt within a wider time frame.
In live operation you can even see clearly with thenaked eye that the robots controlled by KeMotion move more smoothly that ones with conventional control. Thanks to look-ahead motion planning, jerky braking and acceleration processes that are commonly found when several robot arms are in use in shared workspace are a thing of the past.Reduced mechanical strain, fewer machine vibrations, reduced energy consumption with higher throughput and increased productivity are the practical benefits for the user.
In short, «Intelligent Motion» look-ahead path planning with KEBA’s KeMotion robot control comes with great savings potential. Both the energycosts and the maintenance required for a plant can be reduced effectively as a result.Besides this, productivity is also increased effectively as the individual cycle times are shorter.
Ultimately a principle familiar from driving lessons proves to be true of robotics, too: «If you always think ahead you will reach your destination more safely and more economically and in less time.»
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