Omron Automation & Safety
Proximity Sensors, Light Curtains

 

Festo
Proximity Sensors, Vision Systems

An extremely broad category, we group these areas together under the basic premise that they take inputs from the external world into a machine, so that the machine can operate accordingly. It is an important distinction to note, however, that to meet standards for human safety around machines, specifically safety-rated components must be used in accordance with applicable standards and a Risk Assessment procedure must be followed. We highly encourage consultation with a professional when applying safety hardware to a machine or process.

Photoelectric Sensors

Photoelectric Sensors operate on the general principle of light being reflected from (or blocked by) a target, which then triggers a response from a photo-sensitive receiver – turning on or off an output based on the presence or absence of an object. They come in many flavors, including diffuse-reflective, through-beam, retro-reflective, and background suppression. One large subset of photoelectric sensors is fiber optic sensors, which allows for use in tight spaces or harsh environments.

Photoelectric Sensors
Proximity Sensors

Proximity (“Prox”) Sensors operate on the principle of a target interfering with a generated electro-magnetic field when close to the sensor – most commonly a metal target and an inductive proximity sensor, but options also exist for capacitive proximity sensors, which can detect the presence of other non-magnetic materials such as water (and thus body parts). These typically have a short range (up to about 20mm), and can be very cost-effective in quantity.

Proximity Sensors
Measurement Sensors

Another broad category, these are sensors that measure something – for example, a laser sensor that measures distance to an object very precisely and relays that information via analog outputs or communications to a PLC. There are 2D measurement sensors for profiling a workpiece, contact sensors for detecting object size, and many, many other options. These can range from low-hundreds to many thousands of dollars.

Measurement Sensors
Limit Switches

A simple, rugged way to detect a part, Limit Switches operate by physical contact between the object and sensor – frequently with a roller/lever mechanism. These are very cost-effective and easy to apply and maintain, and find their way into extremely harsh, dirty environments.

Limit Switches
Ultrasonic Sensors

Ultrasonic Sensors operate by emitting a low-frequency vibration, and measuring timed response echo as that vibration bounces off a target. These work well in applications like tank level monitoring, where you have a large, flat surface (liquid in the tank) to reflect the sound waves from. Measurement ranges commonly go from a few inches to about 50 feet.

Ultrasonic Sensors
Vision Systems

Vision Sensors and Vision Systems operate by taking a picture of the target and applying software to inspect for various features such as position, orientation, defects or missing parts in an assembly, bar-code markings or writing, and various other things. They are commonly used for quality control – making sure caps are on bottles, for example – and in coordination with robotics, detecting the location and rotation of a part to be picked. Vision Systems are more complicated than other sensor technologies and require careful attention to lighting and lensing, as well as specialized software and programming. Basic Vision Sensors (“smart cameras”) start at around $1500. High-speed, multi-camera Vision Systems can be in the tens of thousands of dollars.

Vision Sensor
Encoders

Encoders can be rotary (such as on the back of a servo motor) or linear (tape-scale and read head), and detect position for use as feedback in a motion-control application. It is frequently desirable to have a ‘secondary’ linear encoder on a long actuator to account for any mechanical inaccuracy in the transmission between the motor and load, such that a user is able to measure the exact position of the load directly, instead of inferring it based on motor position. These can come in incremental or absolute flavors and have varying resolutions.

Encoder
Safety Light Curtains

Safety Light Curtains are linear arrays of photoelectric emitters and receivers in a through-beam configuration, and are used to detect an operator entering a dangerous area – at which point the safety outputs are meant to turn off the dangerous machinery and protect the user from injury. The resolution of beams (for “finger”, “hand”, or “torso” detection) and distance from the hazard must be taken into account, along with the stopping time for the hazard and the OSHA hand-speed constant of 63 inches/second, such that the machine has enough time to stop before the user can get to the hazard. Safety Light Curtains are commonly used with loading/unloading stations that require frequent operator interaction.

Safety Light Curtains
Safety Laser Scanners

An alternative to light curtains and hard-guarding (fencing) for a work area, a Safety Laser Scanner can monitor a 2-dimensional plane and watch for intrusions by operators into a programmed “Safe Zone”. These are commonly used on Automatic Guided Vehicles (AGV’s) and in Robotic work-cells.

Safety Laser Scanner
Safety Mats

A Safety Mat operates when a user (or some heavy object) steps onto a rubberized mat consisting of two electrically charged plates in parallel. When the user steps onto the mat, the safety outputs activate and the safety function (for example, stopping a robot) occurs. Safety Mats are great for dirty environments, and can be a cost-effective way to guard an unusually-shaped work area around a machine.

Safety Mat
Safety (Interlock) Door Switches

Safety Door Switches come in a variety of shapes, but the basic premise is to monitor and/or control user access to a hazardous part of a machine or process. They can be a coded-magnet sensor for simple, reliable detection of door open/closed status, or tongue-style switches that can include powered solenoid-locking functions to lock a user out of a given area while a dangerous process is being performed.

Safety Door Switches
Emergency Stop Devices

Emergency Stop Devices (“E-Stops”) are required by NFPA codes on all machinery, and should be placed within arm’s reach for any operator of a hazardous machine or process – these are intended to immediately stop a machine in the case that something has already gone wrong. E-Stops come in a variety of forms, such as the ubiquitous red-on-yellow mushroom pushbuttons and rope-pull switches. Frequently these contain dissimilar contacts, such as one normally-open and one normally-closed, to indicate situations like cut cables or stuck contacts.

 Emergency Stop Devices
Safety Monitoring Relays

A Safety Monitoring Relay is a panel-mounted electronic device that takes inputs from safety devices (such as Door Switches, E-Stops, and Mats) and provides the force-guided redundant relay contacts meant to switch power from the hazardous device (a saw-blade motor, for example). Additionally, Safety Monitoring Relays have redundant checking processes that monitor operation and condition of the safety devices, to check for things like simultaneous operation, wire breaks, or stuck contacts.

 Safety Monitoring Relay
Safety Controllers

Think of a Safety Controller (or “Safety PLC”) as a Monitoring Relay with additional programmable control functions. A user wires in all their safety devices (light curtains, mats, scanners, door sensors, etc.) and uses simple logic programming to dictate machine safety behavior. Frequently, if a machine requires 3 or more Monitoring Relays, a Safety Controller may be a more cost-effective solution, especially in cases that require muting or safety zone-control.

Safety Controller