A modification which allows the piezo disc to be stressed in the radial axis does work well although it does increase the total compliance of the bed mounting slightly. This method was found to be unsatisfactory when used directly across the piezo as the output had two peaks, possibly from distortion to the disk during drilling. This was accomplished with a 3D printed parallel mechanism.Ī later development of this eliminated the parallel mechanism by having a piezo with a hole in the center through which the build stage mounting operated. To minimize the compliance, Leadinglights developed a piezo disk mounting that converted increasing pressure on the build stage to reducing pressure on the piezo element on the thickness axis. Getting good thermal isolation is easiest done by moving the piezo element away from the heated bed. It is not generally practical to install piezo discs under the print bed in the same way as FSR sensors pioneered by Johann as piezo disks have a significant decline in sensitivity at temperatures above 50✬. None of the above problems have been particularly difficult to overcome and a number of sensors are in regular use without any problems being found. This has not been confirmed in practice although it may be more severe in a heated environment There is some documentary evidence that PZT deteriorates with time.The do not detect a status and if the nozzle is already in contact with the bed when a call is made to perform a Z probe operation then that call may fail. Piezoelectric disks detect an event, that it the nozzle coming into contact with the bed.If the low end cutoff of the conditioning electronics is too low then changing temperature may be interpreted as a nozzle contact. PZT suffers from a pyro-electric effect which causes a voltage to be generated with changing temperature.Piezoelectric disks suffer loose sensitivity with increasing temperature, this is particularly evident in "no-name" units where a maximum usable temperature of 50✬ or 60✬ is the maximum working temperature.Z probing operations should take place only after any mechanical shaking from X or Y movement have died down. Most mountings explored to date have some degree of cross talk, that is the piezo will respond to X or Y movements.The signal conditioning requirements for the output of a piezoelectric disc to be used by a micro-controller are very undemanding, it is even possible to use the output directly with only overvoltage protection. They are also very inexpensive, being perhaps only a few percent of the price of any cometing sensor (e.g. Conversely, the compliance of a sensor using the radial axis will be higher than one using the thickness axis.Īlthough naked piezoelectric discs must be treated with care, they are exceptionally robust when installed. The voltage output from a piezo disk using the radial axis, that is one allowed to flex, is about 3 times the output from one where pressure is applied to the surface, in the thickness axis. The very high sensitivity of piezoelectric discs is the single greatest advantage, outputs of several volts in response to a light nozzle contact are typical while repeatability may be in the region of a few µm. There are other directions of sensitivity, particularly that between the two surfaces of the ceramic disc: This is known as the thickness axis or sometimes as the axial axis. ![]() Expansion or contraction of the ceramic in this direction will cause the brass disk to which the PZT is bonded to dome outward or inward. The direction of this is determined by something called "polling" which is done in manufacture and in piezoelectric disks this is radial, pointing from the centre of the diameter outwards. The piezoactive material in most piezo disks is a ceramic known as PZT which expands or contracts when a voltage is applied to it it also generates a voltage when it is put under pressure or strain. The first known use of piezoelectric discs in this manner was by Njål Brekke who fitted piezo discs to respond to the bed pressure transmitted through bed leveling springs. ![]() There have also been several postings in 3D printing forums speculating that they may be usable as nozzle touch sensors for FFF (FDM) 3D printers. Inexpensive piezoelectric discs have been used for touch sensing in the past on projects like maze running robots.
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