Piezoelectric bender problems

[ClydeCrashKop]

Hi ETO friends
I want to build some pneumatic valves like this.

I got the piezo bimorph bender at https://www.steminc.com/PZT/en/piezo-bimorph-actuator-for-pneumatic-valves-25mm
Piezoelectric bimorph actuator. Uses include pneumatic valves, small displacements with considerable blocking force for its displacement.
Piezo Material: SM411 (nominally equivalent to PZT-5J).
Dimensions: 25mm - 0.984"×7.1mm - 0.279"×0.50mm - 0.0196"
Free Length: 18mm - 0.708"
Displacement: 0.05mm @ 24 Vp-p .002" (50 μm)
Blocking Force: 50N or 180 Oz.

There is no data sheet or wiring or control examples. On their website it says.
"Available product information/specification is the one seen on the product's page. Nothing else can be provided.
We will not send any printed information along with the shipment so please check it online."

I found general info and wiring possibilities online. Wired serial did nothing.
Wired parallel like this,

I got the 0.002" movement but it is very weak compared to the 50N, 180 Oz. force in the specs. Pressing on a postage scale at 24 volts, I got plus and minus 0.15 ounce pressure with a total of .3 ounce pressure at 0.002" movement.
At 50 volts, .62 OZ. pressure.
At 70 volts, .80 OZ. pressure.
At 100 volts, 1.00 OZ. pressure. But that is way less than the 180 Oz. force in the specs.
Wired parallel like this,

the movement was all in one direction instead of +/- from center and was slightly stronger. At 60 volts it moved 0.002" at 0.80 OZ. force.
Still not close or usable.

Is there another way to drive this thing?
What am I missing?

 

[alec_t]

In the second pic, shouldn't the lower bender be up the other way?

 

[ClydeCrashKop]

On this picture with the potentiometer, it actually bent above and below the center strait / off position.

 

[jjw]

https://www.piezo.com/tech2intropiezotrans.html
60N force must be wrong.
Highest force I saw in the product pages is below 1N

 

[ClydeCrashKop]

I think you are right. I only need 2 ounces or 0.6 Newton. It won't even do that.

 

[Colin]

There is a mistake.

Notes: Maximum Blocking force @ 100Vpp is 0.2N for
Piezo Ceramic Bimorph 40x10x0.5mm 2 KHz
SMBA4510T05M - 2 Pc/Set
Manufacturer part number: SMBA4510T05M


Yours will be 0.5N

 

[ClydeCrashKop]

So I emailed my findings to STEMinc. This was their reply.
Thank you for your message.
I am sorry for the wrong information. I just checked our website and I see the Force as 50N where it should be 50mN. I asked our IT person to fix the mistake.
We will issue a refund for you for the purchase of this product and you can keep it.

I think they use terms like Blocking Force and Newtons to camouflage how weak these things are. It is like stepper motors being rated in Kg/cm holding torque instead of the actual working torque it can produce. If I wanted to hold something from turning, I wouldn't use a stepper motor.

 

[dr pepper]

I was thinking 50n is a lot, about 5kg, that would take some pushing over a length like that.
Piezo diesel injectors produce reasonably high force, maybe a little more, but they have a stack of piezo discs, each one moves a tiny amount at high force, adding up to a fraction of a mm or so.