The Pick & Place field is a good example of the application of a high-speed robotic solution: picking up the product, placing it and starting over, performing these operations “on the fly”, that is, with the product in motion at all times. , without the need to stop the product for a robot to act on it, thus shortening the total time of the Pick & Place, and notably increasing productivity.
In order to meet the needs of the application in terms of precision, trajectory, speed and acceleration, it is very important to make a good selection of the different elements of the system such as: type of robot, vision system, product handling clamp , robot controller etc ,. In this way, Pick & Place applications are reaching 120 or more cycles per minute, one cycle being the collection and placement of the product.
APPLICATION SPECIFICATIONS
The first step in a Pick & Place application will always be to specify the needs, to know well what product the robot will handle, the number of product types, and what exactly the robot will have to do, as well as to define how the robotic cell will be to facilitate the operation of the robot when moving and handling the product.
MINIMIZE CYCLE TIME
80% of the cycle time of a Pick & Place application is usually in the movement of the robot, this means that to minimize the cycle time, one of the most important tasks is to minimize the movement of the robot, the more distance it travels the more time the robot invests in that movement, and fewer cycles per minute can be performed.
It might be thought that these movements on many occasions cannot be minimized, since the product probably requires it, but they can be minimized based on the placement of the robot in the XY plane, in such a way that its waiting position subsequently reduces the robot movement. Also the height of the robot can be a determining factor, avoiding large movements in the Z axis that waste valuable time.
SELECT THE ROBOT
There are many types of robots: Cartesian, SCARA, DELTA, anthropomorphic depending on their mechanics and number of axes, however, for high-speed Pick & Place applications, the DELTA robot has been shown to be the most complete robot, since Due to its mechanics and the positioning of the motors, it provides great speed and can carry loads of up to 8 kg.
It is very important to consider all the data of the application to select the right robot:
– Total load (weight of the product plus claw).
– Path of the Pick & Place.
– Workspace: both in the XY and Z planes.
– Accuracy
– Synchronism with one or two tapes and placement of the tapes.
– Cycles per minute necessary to determine the speed of the robot, and study the feasibility, as well as whether it is necessary to install more than one robot on the line.
HANDLING CLAW
The handling claw or gripper is one of the most important factors in the Pick & Place application, since its weight, and the waiting, opening and closing times may or may not make the application feasible.
There are several types of clamps, the most common are vacuum and mechanical.
– Vacuum grips are simpler, lighter, and faster, as well as requiring less maintenance.
– Mechanical calipers provide more precision, at the cost of being slower and requiring more maintenance, as well as, usually, being heavier.
The weight of the claw is a vital factor in the system, since the more weight the robot carries, the slower it will move and the fewer cycles per minute it will perform, however, the stability of the product must always be ensured while it is being transported. taking into account the great acceleration and speed to which it can be subjected in the process of leaving the product
ARTIFICIAL VISION
Robotics and artificial vision are increasingly linked every day, in many robotics applications it is necessary an artificial vision system that sends the coordinates of the product to the robot controller and that reports invalid products, or distinguishes between several products to that the robot can classify them.
The artificial vision system must be able to send the necessary information to the robot in such a way that it does not have to stop its production to receive the vision data, in fact, the same
The vision system could be capable of sending information to several robots, with the controller deciding which robot will act on the product. However, there could also be one camera per robot, connected to the same vision controller, for cases where multiple products can come too close together.
On the other hand, it should be noted that one of the most important aspects of the success of an artificial vision system is lighting, it is essential to select a lighting system that allows to see the product perfectly constantly regardless of environmental changes, and to have a good contrast with the rest of the elements that the artificial vision can see, in this process, both the placement of the lighting, as the type of the same, shot, color, or even color of the background through which the product is being transported.
ROBOT CONTROLLER
The idea is to provide the user with an environment where, in a simple way, all the elements of the machine are integrated together with the Pick & Place part and allows the simulation software to make a quick calculation of the cycles / min based on the trajectories to be carried out, of the artificial vision and of the synchronism with other axes also controlled from the same machine controller.
In addition to the correct selection of the robot, the correct selection of the handling gripper, the vision system etc … a fundamental role, probably the most important is the chosen controller.
The idea of having a controller and software with all the integrated machine solution is vital to avoid waiting times between different devices (synchronism with the tapes, artificial vision, robots etc …) and so that the programmer does not have to manage protocols communication between teams that do difficult work and lengthen application development time.