Production Automation Sensors Keep An Eye On Manufacturing Processes
Any time you have moving parts or equipment that does work without the intervention
of human effort it is necessary for some type of sensing or verification of the process. Production automation sensors do the job of keeping an eye on production tasks that run unattended. These tasks that are performed can vary quite a bit. Production automation sensors make sure that humans are aware of the accuracy or inaccuracy of the tasks that automation performs in manufacturing. There are three basic types of production automation sensors, contact sensors, process monitoring sensors, and no-contact sensors. Each of these types has its own unique set of sensing applications in the manufacturing process. The tasks that are done by each of these types is either monitoring a process, detecting conditions, analyzing a process, or calibrating a part or the process.As monitors production automation sensors assess the quality, consistency, and conformity of parts on the production line. This monitoring function would also include the review of assembly operations which encompasses the identification and location of parts used in assembly, and the proper positioning of parts relevant to the assembly process. When performing the detecting function production automation sensors determine if there is imminent danger for the production equipment, the product being manufactured, or the workers near the work cell. This task would also include the detection of malfunctions or breakdowns in the process. An example of this type of sensing occurs when a sensor is installed to monitor a conveyor belt. As products move down the belt there is a small space between each product that has a set time duration. If there is no time duration during which the light beam is broken that is equal to the size of the product, the sensor will shutdown the conveyor because the conveyor is blocked for some reason. This protects the products, automation equipment and the workers near the conveyor. Production automation sensors are valuable for analysis of parts and the process so that problems in the production process can be deterred automatically.
The contact sensor, as its name implies, requires that the end-effector of a robotic device actually touch the part that is under scrutiny. This sensor can be very simple usually incorporating the use of a limit switch. The limit switch is an open loop, non-servo device which means it does not give feed back to the system about information that it gathers and it runs until the limit switch is turned off. These sensing devices are used mostly to detect motion or movement of parts in the work cell where they are located. More sophisticated contact sensors are closed loop, servo devices that provide feedback to the controller once a contact has been made to a part or surface. The feedback can include such information as shape, size, position, orientation, and other factors about the object encountered. The contact sensor is often used in product processing to determine if a product has arrived at the inspection station. As the product moves down the line it encounters the contact sensor which turns on the inspection operation for that product.
Process monitoring sensors are technically not sensors, but do give important feedback to the manufacturing system about the state of conditions in the manufacturing process itself. This kind of information will keep the processes running smoothly by notifying operators of any corrective action that needs to be taken to keep things going.
The no-contact sensors make up a large group of the newest, and growing technologies. These sensors do not touch the parts, products, or environment that they are scrutinizing, but do return valuable information to the controlling system. These devices include those sensors that handle proximity, photo-optic, and vision functions.
Proximity sensors determine the presence of an object using electromagnetic or electrostatic fields. There is a large range in the degree of sensibility of these devices. Some can detect objects at greater distances than others. The sensitivity of any given proximity device is dependent on the application with which it works. There is also a great range of different sizes and shapes of proximity sensors that can be used to do this type of job. These sensors can detect both metallic and non-metallic parts. Metal parts are typically detected with an electromagnetic field by the proximity sensor. Usually the sensor will determine the presence of a non-metallic part using high frequency electrostatic capacitance. A good example of the application of a proximity sensor in manufacturing occurs when a sensor is set up to determine if a bit has been broken during a high speed drilling operation. The sensor is positioned to "see" the end of the bit. If the end of the bit is present then the drilling operation can continue. If the end of the bit is not present, then the operation is automatically shutdown, so the bit can be replaced. In another similar proximity application the sensor determines if there is a bit is in the chuck so that drilling can start. Both of these sensors use electromagnetic sensing to perform their tasks.
A combination of production automation sensors can be used on a production line where products are being placed in open cans. After the cans are filled on a manufacturing line, automation places a lid on each can. Before cans are pulled off the line for packaging by automation, one sensor determines if there is a can on the line below the current checkpoint. If there is a can at the location, then another sensor, located above the line at the checkpoint, determines if there is a lid on the can below it using metal detection. If the there is no lid then the can is diverted before being sent into the packaging work cell.
by: John Mitchell