ΔL = displacement 0f actuator with spring load Performance of a piezo actuator with no load (A) versus an actuator with a low-stiffness spring load (B). On the other hand, the spring reduces the actuator’s displacement only slightly: Therefore, the piezo output force is greatly reduced from its maximum, or blocking, force. In other words, a spring (load) with low stiffness provides very little “blocking” for the piezo to work against in order to generate a force. When the stiffness of the applied spring load is low compared to the piezo stiffness, the piezo output force (F eff) is small. Many piezo applications, such as valve operation, introduce loads that vary with the piezo’s stroke - in other words, spring loads. Piezo output force and displacement with a non-constant (spring) load The actuator’s ability to produce displacement and force depends on the type of load. There are two types of load that can be applied to a piezo actuator: a spring load, which increases as the actuator moves, or a constant load, which does not vary. When an external load is applied (A), the stiffness of the load (k e) determines the displacement (ΔL A) and force (ΔF A) that can be produced. Likewise, at maximum displacement, or free stroke, (ΔL fs) no force is generated. Maximum, or blocked, force (F block) occurs when there is no displacement. ΔL fs = free stroke (nominal displacement) with no external load In piezo actuators, force and displacement are inversely related. The stiffness of the actuator is the ratio of blocking force to free stroke. This force is measured and recorded as the blocking force. A force is then applied to return the actuator to its original length. This “free” operation, as described above, generates the actuator’s maximum displacement, or free stroke. But materials with infinite stiffness don’t occur in the real world, so the blocking force is determined by applying a voltage to the actuator, with no load applied. Theoretically, when the actuator is blocked, it is working against a load with infinitely high stiffness. A “free” actuator - one that experiences no resistance to movement - will produce its maximum displacement, often referred to as “free stroke,” and generate zero force.Ĭonversely, when an actuator is blocked from moving, it will produce its maximum force, which is referred to as the blocked, or blocking, force. In other words, the more force an actuator must generate against a load, the less travel it can produce. This relationship between displacement and force in piezo materials is an inverse relationship. But when the actuator is blocked from moving (by a load applied in the direction of travel), it generates a force. Piezo actuators operate on the inverse piezoelectric effect: when voltage is applied, the actuator contracts or expands.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |