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SHAPING THE SOLENOID FORCE CURVE
Designing the proper solenoid actuator to meet a specific application involves more than gathering information on the required force, stroke and voltage. While these characteristic are certainly most important, information such as ambient temperatures, environmental conditions, mechanical life required as well as other issues are also important to determine suitable performance of the solenoid.
Force generation is a function of power input but the stroke required also plays a critical role. The solenoids shown (see Figures 1 and 2) both have the same ending hold force once completely energized however, the larger units stroke is 25mm vs. 3mm so to achieve the same pull force across the longer stroke, the solenoids size must increase. Within limits, it may be possibly to maintain the size by increasing the power input to get the same force over the longer stroke, which can lead to excessive heat generation and increased cost for higher power electronic controls.
When designing the force and stroke characteristics of a solenoid it is most important to understand the point in the stroke where the maximum force of the solenoid will be needed. Just as a compact car and SUV both carry loads, each has a limit tied to a corresponding cost, (use of fuel), and solenoids are somewhat the same. Many times a solenoid is specified for the highest force at the longest stroke leading to the use of a larger solenoid than necessary, wasting significant amounts of energy as well as adding cost.
Mapping of the "load" force curve of the application will provide critical data to allow for a more precise design of the solenoid force curve to meet the actual load force at any point along the stroke, commonly referred to as "shaping the curve". Utilizing magnetic analysis software (see Fig.3), the design engineer can analyze multiple configurations of magnetic and non-magnetic components and air gaps in a relatively short time. Design consideration is given to permeability of materials and the physical size and configuration of the magnetic and non-magnetic components, as well as reduction of air gaps in the flux path. The final design goal is to provide the maximum flux density at strategic points along the stroke length to "shape" the force curve to meet the application force requirements (see Fig. 4). "Shaping" to the most efficient combination of force vs. stroke provides the best optimized design for size, power consumption and cost.
While we focus on the significance of "shaping" the force vs. stroke performance of the solenoid is just one important factor in the design of a reliable custom solenoid actuator. As mentioned previously, environmental factors, mechanical life requirements as well as performance issues pertinent to the specific application must be considered. Many times, features designed in to accommodate mechanical life or environmental requirements such as seals and bushings can adversely affect the "optimized" force vs. stroke performance. Care must be taken when incorporating these features for the least affect on the performance of the solenoid.
- Wayne Groth, TLX Sales Engineer
Fig. 4 - Typical Solenoid Force Curve
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Fig. 1 - Latching Solenoid
Fig. 2 - Linear Proportional Solenoid
Fig. 3 - Femm Plot |
