Factors to consider when purchasing a robot

With the large number of different types of robots in the market, the selection of the best can become a problem. Unlike other teams, the robots are not easy to classify and assess. They have different axes and lengths of career, little uniform specifications and meet limited industrial standards. This makes it difficult comparisons.

A unit of programming with guided manual complements the control panel of the robot.

Without the help of a series of guidelines the selection of a robot can become a difficult exercise. In order to be able to compare with each other, we should start with the most elemental. Knowing these foundations, already have been an important step to make a proper choice.

The route that a robot can do, his career, depends on the size of the piece, the location of the point of injection and the dimensions of the machine. To simplify, this distance is often defined by three axes: we ceñiremos to axes X, and z, but it is important to know that not all manufacturers define their careers in this way. The X axis, depends on the depth of the piece. To manipulate a cube, for example, a robot need enough career to reach the cube and extract it from the mold. The axis and the vertical race, is the distance determined by the height of the machine and the height of desired drop. The robot must be sufficiently high to allow the piece to save the machine, but low enough to drop the pieces to a reasonable height on the ground. On the Z axis, the transverse, depends on if the robot loose piece on one side of the machine or behind it. Part of this race is used to save the machine and the rest to the position in which it drops the piece. The easiest thing to determine the desired career is want to draw a picture, describing not only the race but also other issues of concern, as the auxiliary equipment or supporting columns.

How much weight will manipulate the robot? The payload is the sum of the weight of the piece and the hand grip of the robot. Although the weight of the piece is commonly known, is not the case in the hands of grip, whose weight is estimated and can be known through the supplier.

More important than the payload is the couple, the tendency of a force to produce a torque and rotation on one axis, and function both the payload and the distance to the focal point of the hand grip of the robot. To make sure that a robot can manipulate a piece, should compare the applied torque, the of the piece and the hand grip, with the couple that the robot can hold.

How are benefits assessed? The benefits of a robot many times are presented in terms of speed peaks. But this information is not complete, not to be of exposing the accelerations. For example, Figure 1 shows the speeds of two robots, one with a peak speed of 4 m/s (above) and the other with 3 m/s (below). One could conclude that the fastest robot is one that has a higher peak speed. However, both robots can travel the same distance of 2800 mm at the same time, a second. This is possible because the robot with lower tip speed has a higher (45 m/s2) acceleration to the other (13.3 m/s2). It is more useful to know the time required for a robot to explore a specific distance, information which should provide it the manufacturer.

Another important question that one must do when purchasing a robot, is if it is easy to handle. The screen of the control has a great influence on the simplicity of a team, to improve its ease of use if you include a graphic interface, an intuitive touch screen and a separate accessory to guide the user. The type of control also affects other issues. Robot controls integrated with the machines share common screens and reduce delays by means of direct communication between two controls.

As for reliability, it is interesting to do with digital components such as a controller based on PC Digital drives with servo motors. As in any other team can always have a bug, for what should be fixed in the guarantee, which vary widely. To the value of a guarantee, it is important to look at the list of items subject to wear that are excluded from coverage. Taking into account the differences between the guarantees, a three-year-old not always has to be better than a one.

Robots are subject to the General provisions of the industry in regards to security and, in the case of robots to injectors, also affects the rules concerning this kind of machines.

It should be informed also of this type of issues, in particular those relating to jobs, the installation of limiting mechanical, elements of security in the area of the vertical drop, and others.

The price, of course, is one of the decisive factors that often determine the purchase, but it is very important to take into account its financial impact on a general system. For example, must be taken into account the savings that can be obtained by reducing the downtime or increasing the cycle time.

For example, in a factory with 6,000 hours of production, a 1 per cent reduction in downtime of the robot in a fuel transfer of 1,800 tons, can provide a savings of up to 8,800 euros per year, while that an improvement in 0.5 seconds in the cycle in a cycle of 10 seconds and 200 machine tons can make annual savings of 12,300 euros.

In certain applications without doubt worth the purchase of a robot for top performance.

Finally it is important to note that the robot is a part of a whole line of injection: their performance, reliability, safety and cost play an important role in the system as a whole. Therefore, the robot is chosen must respond to the objectives set for the entire system.

Figure 1. Comparative speed/Acceleration shows that two robots with different peaks of speed can go a same distance at the same time.