Ring and Track System From Bishop-Wisecarver Provides New Options For Machine Design
The Hepco ring and track system from Bishop-Wisecarver lets engineers design machines with linear, circular or combined motions. Available in a wide variety of sizes and profiles machine designers can incorporate simple circular motion to complex motions by combining ring segments with straight sections of rail.
Other Options
Other options include gear tooth options for drive mechanisms, automatic lubrication, and moment load carriages for greater rigidity. Floating journals compensate for misalignment. For more information or design assistance contact ISC Companies.
Choosing the Right Photoelectric Sensor
Photoelectric sensors use light to detect the presence or absence of an object. The main advantages of photoelectric sensors are noncontact sensing of objects and greatly extended sensing ranges. Photoelectrics have been engineered to address a vast array of industrial applications in environments ranging from clean rooms to foundries. Photoelectric sensors can provide simple on/off switching or provide analog outputs and interface with any logic system. The intent of this article is to provide a primer of the basic types of photoelectric sensors and how they operate.
There are many factors to consider when choosing a photoelectric sensor. The specific demands of your application will dictate the sensor required for the job. Some of the questions you should consider when applying photo electric sensors include:
- What range is required (how far is the sensor from the object to be detected)?
- What is the nature of the environment (clean/dusty)?
- What access do you have to both sides of the object to be detected (is wiring possible on one or both sides of the object)?
- What size is the object being detected?
- Is the object consistent in size, shape, and reflectivity?
- What are the mechanical and electrical requirements?
- What kind of output do you need?
- Are logic functions needed at the sensing point?
Modes of Detection
While all photoelectric sensors use light as a medium to detect their target, how they operate can vary greatly and are dependent upon the needs of the application. The basic types of photoelectrics are outlined below.
Thru-Beam
Source and detector elements are mounted in separate housings and aligned facing each other across an area which the target object crosses. Detection occurs when an object blocks the entire effective beam (the column of light that travels in a straight line between lenses)
Reflex
The source and detector are mounted in a single sensor housing and are positioned parallel to one another on the same side of the object to be detected. The light beam is transmitted from the source to a retroreflector that returns the light to the detector. Detection occurs when the target object blocks the entire effective beam.
Diffuse Reflective
The source and detector elements are mounted in a single sensor housing and are positioned on the same side of the object to be detected and aligned with crossed fields of view. When the target moves into this area light from the source is reflected off the target surface back to the detector and detection occurs.
Background Suppression
This is a special type of diffuse reflective sensor that combines extremely high sensing power (excess gain) with a sharp optical cutoff. This allows the sensor to reliably detect targets regardless of variations in color, reflectance, contrast or surface shape, while ignoring background objects that are just slightly beyond the target range.
Color Sensing and Contrast Sensing
These sensors are frequently used in printing applications where subtle variations of color on the same object at the same distance can be detected.
Fiber-Optic Sensors
Fiber optics can be used with any type of photoelectric sensor (through-beam, reflex etc). Fiber optic cables (glass or plastic filaments in a protective sheath) are used for specific applications such as detecting very small objects or used in high temperature environments.
Sensing Range
In general, thru-beam sensors offer the greatest range (most power), followed by reflex and then diffuse reflective sensors. Operating ranges vary, and there is some overlap among types and models.
Excess gain is a measure of the sensing power available in excess of that required to detect an object. The following excess gain chart shows this measurement graphically. Find your required range on the x-axis of the graph. Then move up to the curve to read the excess gain value from the y-axis. An excess gain value of 1 is the minimum level required for sensor operation. Typically excess gain levels ≥ 10 for reliable sensor operation are recommended. In areas where contamination is present (dirty/dusty environments) increased sensing power will be required to assure reliable operation. ISC Companies can provide application assistance based on you specific needs.
ISC Companies Sensors & Controls Group inventories a wide variety of photoelectric sensors as well as laser and ultra-sonic sensors, capacitive and inductive proximity switches, and mechanical limit switches. Contact your ISC representative and we will be happy to provide you with the applications assistance you need for all your sensing requirements.
