Industrial robots—increasing profitability

An industrial robot is a programmable machine for the assembly, processing or handling of workpieces. Industrial robots—also known as industrial manipulators—are specially designed for use in an industrial environment and are used for instance in automotive production. They usually consist of a robot arm, control and gripper or tool. Such robots are often equipped with sensors—once programmed the work sequence is performed autonomously or can also be varied depending on sensor information.

Which industrial robots are there?

Industrial robots are available in a wide variety of designs from various manufacturers. They are usually purchased as a basic unit and then adapted to their task using tools that correspond to the desired application.

Industrial robots are grouped according to kinematics:

• Parallel kinematics

• Serial kinematics

Serial kinematics consists of an arrangement of arm parts. Parallel robots, however, use linear actuators attached to a moveable platform. With parallel robots, the actuators are not loaded with the mass of the adjacent actuators and links, which result in a low moving mass and more precise mechanics. A hybrid robot is a combination of a serial robot and parallel kinematics with actuators that are not completely fixed.

Parallel kinematics and serial kinematics

Payload is a decisive criterion for industrial robots. It indicates the maximum mass that can be attached to the end of the gripping arm. The range for robot arms is from 2.5 kg to approx.1700 kg. But accuracy and dynamics are also important variables. Today's industrial robots usually have six axes—a minimum of three axes is required to be deemed an "industrial robot".

The automobile manufacturers use industrial robots in large quantities for painting and assembly work. The great advantage of this is that movement sequences can be independently programmed, thus covering different handling sequences of various vehicle models. Due to the large amount of robots used, these are now produced in great numbers, which has led to a sharp price decline. As a result, articulated robot arms now are also used in many other industries.

Gripping technology - the heart of the system

Gripping technology is at the heart of every industrial robot—it is responsible for the optimal use. The robot arm is modeled after the human arm. Accordingly, it is also the robot arm that people unfamiliar with industry bring to memory when thinking of industrial robots. However, this is only one of several types, because the following gripping systems are available:

• Vacuum gripper

 • Mechanical gripper

 • Magnetic gripper

The gripping system is the connection between the robot and workpiece. Grasp is either astrictive, impactive or ingressive. The robot arm consists of a series of rigid links that are connected by sliding and swivel joints and are thus multifunctional. The joints are controlled using actuators. The base is at one end of the arm and the free-moving part at the other, which is equipped with a gripper or tool.

Gripping technique of an industrial robot

Actuator systems—AC servomotors with resolver

Today AC servomotors are used to actuate modern industrial robots. These are equipped with a resolver that provides two signals when the axis rotates. It is fixed to the motor shaft and permits the generation of a counting pulse and the detection of the rotor position. This makes it possible to detect the position of the axis and the robot.

Previously motors were equipped with two different systems to detect position and rotor position. They were connected with separate cables and mounted to the actuators, resulting in two extra cables having to be routed to the control system in addition to the power cable.

Robot control—coordinating axes and gripper

The actual robot control is responsible for coordinating the axes and for the gripper to move along the programmed path with the desired speed and accuracy. It also processes the sensor signals of the gripper and gripper actuators. In some applications, complex tasks result from handling procedures, so that different movements have to be carried out.

In recent years, much has been done in the field and robots are now controlled by PC. In 1999 the company Dortmunder Roboterbau designed the first robot with PC control and a touch-screen user interface. PC systems have now become more sophisticated, which has brought many advantages. This includes BUS technology, which allows simple interface to the robot axes and the other peripherals. Various programming languages ​​have been developed for use by manufacturers, such as NQC, VAL / VAL2 / VAL3, KRL and RCCL. In the future, robot programming will be as simple and user-friendly as possible.

A further control possibility is the use of a programmable logic controller (PLC), which makes it possible to control the robot. In this case, the PLC is connected to the robot together with sensors and the actuators via an interface. Sensors, such as light barriers, are inputs to inform the robot of movement. Actuators, on the other hand, are connected to the outputs of the robot, such as the gripper arm.

Robot applications and PLC are usually connected using a fieldbus, thus reducing the complexity of wiring. In the meantime, Ethernet-based fieldbuses like Profi-Net, which are flexible and fast, are in use.

Protective equipment—protecting employees from possible hazards

Industrial robots increase profitability and facilitate physical work—but they also entail risks and dangers. In order to protect people from these dangers, there are appropriate safeguards. One such method is to separate the work areas of people and machines, since a robot is not able to perceive its environment. Risk analysis is necessary to ensure that operator protection is selected correctly.

Only when all the potential hazards of a machine have been determined, the risks identified and the necessary protective equipment defined, can the appropriate protective measures be put in place. These must protect workers, but they also must not limit the operability and functionality of the robot.

A distinction is made between:

  • Separating safeguards
  • Non-contact safeguards

Protective grids, fences and cladding serve as separating safeguards. These are permanently fixed between employees and the danger area. Mobile protective safeguards are wing doors or sliding doors, which have the same features as fixed devices, but the opening process is monitored. For example, the machine automatically stops as the user enters the area.
Light grids and light barriers are widely used as non-contact safeguards. If the light beam is interrupted, the machine switches off. Special light grids recognize fingers or other body parts and are also used as safeguards. They have the advantage that they are significantly more flexible. In addition, they can be automatically linked with systems and are able to distinguish between material and human beings.
Light curtains allow for relatively flexible installation, but the distance between the light curtains and the hazardous movement is dependent on shutdown time.

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