Motion Control Resources
Evaluation of SMAC’s Models: LCA/S Versus Pneumatic Actuators LVDTs
SMAC Moving Coil Actuators, Inc. Posted 06/26/2015
Linear variable differential transformers (LVDT) are used to measure displacement. LVDTs operate on the principle of a transformer. As shown in Figure, an LVDT consists of a coil assembly and a core. The coil assembly is typically mounted to a stationary form, while the core is secured to the object whose position is being measured. The coil assembly consists of three coils of wire wound on the hollow form. A core of permeable material can slide freely through the center of the form. The inner coil is the primary, which is excited by an AC source as shown. Magnetic flux produced by the primary is coupled to the two secondary coils, inducing an AC voltage in each coil.
The main advantage of the LVDT transducer over other types of displacement transducer is the high degree of robustness. Because there is no physical contact across the sensing element, there is no wear in the sensing element.
Because the device relies on the coupling of magnetic flux, an LVDT can have infinite resolution. Therefore the smallest fraction of movement can be detected by suitable signal conditioning hardware, and the resolution of the transducer is solely determined by the resolution of the data acquisition system.
A pneumatic LVDT actuator converts energy (typically in the form of compressed air) into mechanical motion. The motion can be rotary or linear, depending on the type of actuator.
Applications of pneumatic LVDT actuators are used with switches, sensors, grip/pick or place, in addition to countless industrial purposes.
A Linear Variable Differential Transformer (LVDT) can convert this motion in to an electrical signal.
Pneumatic LVDTs actuators are use in automatic gauging applications or for accessing details that would be difficult or impossible to reach using conventional spring push probes. Some materials such as glass or plastic, for example, require low tip forces to avoid deforming the component and contact tip materials that do not leave a mark.
- Accuracy (% of reading): 0.5-0.7
- Measurement Range (mm): 2-10
However they have clear limitations that are overcome by SMAC actuators.
- Compressed air makes movement and positioning imprecise
- Not able to move to precise location on whole stroke length
- NO SOFT-LAND approach (need additional soft tips that wear out)
- NO Acceleration variability
- NO force management
- NO variable programing possible
- Noise pollution
- Cycle limitation 4 HZ
- Carbon foot print (use of total energy)
- Lifetime limitation 10mil
- Required external support units, AIR, controller…
- Limited reporting capability
- External controller needed
SMAC actuators over whelming usage arguments are:
- 100% confirm and report over whole length of stroke
- Speed programmable/variable and reportable
- Force programmable/variable and reportable
- Lifetime 100 million vs 10 million
- Cycles up to 100Hz vs 4 Hz
- SOFT-LAND and 1 Nm confirm force if needed
- Build-in controller with most units
Proven applications examples like: Pick and place, thread checks, bore and gauging, critical dimensions check, feeding tensioning control(film or weaving), welding control, pin-insertion of connectors(position and insert force-check) couture verification, effort verification of touch screen functions, switch tests, knobs (human interface devices), durability, etc.
Utilizing SMAC’s Actuators (size and versatility variety) enables the OEMs and Suppliers to increase quality, decrease reject % and enables more detail reporting of dimensional data to support all aspects of manufacturing and quality.
For a Quality, Manufacturing, Testing/Durability department. SMAC actuators present the way to have more capability of checking, verifying and reporting of processes, finished parts or production steps to ensure 100% positive outcome with verifiable reporting capability.