It has a slot through the side to allow the cables to come through with the ceramic surface facing the bolt (seems to be the most sensitive way of setting up the sensor). The piezo sensor is setup to be flexed by a M2 bolt in it's centre with it supported around its edge and clamped in place by the parts screw in lid. It is printed with only 15% infill with a full layer every 5 layers at 0.8 layer height and does touch the plate with the bulk of the part (except the thread), this ensures maximum insulation from the heat due to creating multiple layers of overlapping air pockets all round the piezo sensor. The lower part holding the piezo sensor is attached using existing M5 thread in the bottom plate and is attached from under the plate from outside the printer and holds the piezo inside via a screw in cap. I have not got a piezo amp board and multi sensors yet, just recording and watching the piezo output on a scope at the moment and I am able to the faintest touch on the bed with just one sensor (I mean a piece of filament touching it faint) without any noise from the motors moving around. The piezo disc I bought locally (taken out of a piezo buzzer from Jaycar) seems to have plenty of trigger sensitivity with the springs I am using for bed levelling (springs are out of AA battery holder spring for the negative side of the battery) and showing no sign of being affect by the heat. Initial tests show on the Tevo LM running for 6 hours, with a bed temp of 150 * Celsius and full enclosure with air temp of 60* Celsius, that the piezo is not exceeding 39* Celsius (keeping in mind the ambient room temp is 32* Celsius to begin with), in this situation I have to tape the BL Touch pin up and not dream of running a calibration before hand if the printer has been printing before hand. The design incorporates some heat shielding/insulation built into the piezo holder as well as keeping the piezo as far away form the heated bed as possible. So I decided to design up a solution for my Tevo Little Monster delta printer to suit the 27mm piezo disc for under-bed detection. So I have an Ir sensor that is "ok" but this suffers also from changes in the build surface and I end up having to reset the Z-offset dependant on what material is being used. This is made worse for me as I use a lot of different filament types, a heated enclosure and change the build surface dependant on the material being printed which means I am constantly wanting to run a calibration before each print. Considering this crappy sensor uses a bit of heatshrink to set the probe height and length to hall effect sensor, when it is mounted just in front of the hot air coming off a hotend, it is just a crap design all round. 2 to 5 mJ/cm³ of mechanical work and a bending actuator achieves around 10 times lower values.So I got completely sick of how crap the BL Touch is for both accuracy and repeatability on sensor/bed height detection let alone the fact it will randomly drop the probe and ruin prints. A longitudinal piezo actuator can perform approx. The light blue area in the working graph corresponds to this amount. This case occurs when the load stiffness and the actuator stiffness are equal. The mechanical system is energetically optimized when the area reaches its maximum. However, only a fraction E out of this total amount can be transferred to the mechanical load. The energy amount E mech, that is converted from electrical into mechanical energy when an actuator is operated, corresponds to the area underneath the curve in fig. 9. Approximately 30 N/mm² can be achieved here.Īccordingly, the determining parameter for the mechanical energy E mech = (Δ L 0 F max)/2 to be attained is the actuator volume. The cross-sectional area determines the blocking force F max. At nominal field strengths of 2 kV/mm, displacements of 0.10 to 0.15 % of the length are attainable. In longitudinal stack actuators, the actuator length is the determining variable for the displacement ΔL 0.
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