how to exert spring like pressure by using actuators or solenoids

[Robert Milton]

here is a question i have been wrestling with, how do i control 2 different length from an extended shaft out of an actuator or solenoid,...i need 2 different settings or 2 different length of extensions so that i can apply 2 different amount of pressure to the targeted lever. The size of my apparatus can fit in shoe box. Within that space i have few plates and spools situated on a shaft driven by a small electric motor. And at times i need to exert pressure/weight against a lever that i placed so i can move or push these spools and plates closer together, [then of course when need be i would have to remove said pressure by retracting said shaft.]
I was able to provide said pressure with a simple 5 inch long spring and used a solenoid to release pressure. But later I discovered my apparatus needs 2 different amount of pressure settings [which I thought it can be accomplished by extending a shaft coming out of a solenoid or actuator by anywhere from 5 to 30 mm],..i was thinking of an actuator with some strength. [Stepper motor or logic controller system would be to expensive for this simple apparatus] . But how to control these 2 different lengths of extended shaft and what would be the cheapest way is my problem. Any ideas?

 

[dougy83]

Well, I don't think open-loop control (i.e. just connecting a set voltage to the solenoid) would be very suitable here, and would recommend using position information of the shaft to control the driving current. e.g. a linear/slide potentiometer could be connected to the solenoid shaft to give feedback to the controller. I would use a chopper or PWM controller so that you don't have heaps of heat to deal with.

What's the peak current of the solenoid? if it's <1.5A, it might be possible to use just an MC35063 (SMPS controller) to control the position. The position can be changed/set by changing the voltage or series resistance to the slide pot.

EDIT: here's an example slide pot (45mm travel) https://au.element14.com/bourns/pta4543-2015dpb103/potentiometer-slide-10kohm-250mw/dp/1857341

EDIT: you could also use an RC servo motor to do the same thing. It would use less power too. The servo controller could just be a simple timer (e.g. LM555) with switched resistor network to adjust the control pulse signal.

 

[jpanhalt]

here is a question i have been wrestling with, how do i control 2 different length from an extended shaft out of an actuator or solenoid,...i need 2 different settings or 2 different length of extensions so that i can apply 2 different amount of pressure to the targeted lever.

There are such things a two-position model servos, but even a regular servo may work. Why do you need the solenoid? Why not just work the lever directly with a servo?

John

 

[Robert Milton]

Thanks for the response Dougy83, I will have to look into your suggestion. i forgot to mention that the operator of this apparatus will have to use a remote control to get it to operate. [like remotes used in garage door opener, or car doors] therefore we are limited to a certain degree of what the operator can do. I was thinking,...what if i still use a spring to create and exert the 2 sets of pressure i need and use a strong actuator or similar unit and have the shaft of actuator attached the lever from opposite end, by retracting the shaft i would pull back on the spring hence controlling the pressure in a sense. Maybe i should make & post a diagram next time

 

[ClydeCrashKop]

How about something like this?

 

[Robert Milton]

Hi John thanks for the response. I am trying to achieve this goal with under 20 dollars if my idea is to survive,....2 position servo motor is higher i think,..i will be posting a diagram so maybe that might help you guys understand my dillemma then maybe help me out with it,...thanks

 

[Robert Milton]

thanks Clyde i will be posting a diagram soon then maybe you will have a better idea regarding space available to me in this box .

 

[jpanhalt]

New servos can be gotten for less than $3 (**broken link removed**). Standard Hitec servos from a LHS are about $8.00. If you know any modelers, older ones will be free.

A two position drive can be done with a microcontroller (e.g., 12F509) or NE555, which are each less than $1.00 (DigiKey prices). All you need in addition is a switch and a few resistors and capacitors.

The cheapest solenoid on DigiKey is $21.00, if that will work. Others range up to $35. Then you still need the springs, switch, and whatever else will be need for an as yet unfinished mechanical design.

John

 

[Robert Milton]

Hi John,.....I will look into your advise and i have to research next couple of days because i never worked with Micro controller and servo,...i am assuming the servo motor has 2 positions that it can attend with the help of micro controller, and if thats the case then maybe i can attach an eccentric shaped plate to the servo in the effort of delivering the 2 different settings for 2 different pressure amount that i am hoping to exert against that lever. ,...Here is a diagram on how i used the spring and solenoid in the limited space i have for this function in my box. I thank you for your advise. if you have any other suggestions please let me know.
View attachment 66735

 

[Robert Milton]

on a second thought John,..... would an actuator not do the job with less hassles as seen in my illustration photo?

View attachment 66736

 

[Robert Milton]

I posted some illustration photos

 

[jpanhalt]

I can't tell from the renderings what it is you are trying to do.

Multiple positions can be obtained with a single solenoid using an escapement mechanism. I have used solenoids and escapements for controls in the 1950's. Analog watches and clocks used a variety of escapement mechanisms to keep time. If you will, the second hand is accurately positioned to 60 positions each minute... Those watches have all been replaced by electronics that are more accurate and lower cost.

You want only two positions now. What about in the future? With a servo-based system, you can have almost any number of pre-defined positions limited only by the resolution of the servo.

On the other hand, solenoids are an all-or-nothing deal mostly. There is no inherent feedback; although, you could rig something up.

It is not my purpose to convince you to use a servo. I mentioned servos only as a cost-effective and probably mechanically simpler and more reliable approach to positioning something.

John

 

[Robert Milton]

Hi John, all i am trying to do is to be able to push that lever in 2 different settings/distance. first setting maybe would have to push lever 10 mm from its relaxed position and 2nd setting may have to push lever 18 mm, and still be able to bring it back to the original relaxed position. In the picture i posted you can see the actuator's shaft is resting against the lever hence it would mean it is there to push it. from my understanding an actuator is like a screw and a bolt and when powered it extends the screw/shaft and it has much push-power or pressure. [in my last message to you i did not suggest that a solenoid can have controlled extension, i wrote "actuator"] but on the other hand servo can do the same job maybe but from my understanding a servo motor does not have a shaft extending up and down, it has a shaft rotating in various fashion suitable to the customers need,....now the question is how do a rotating shaft or even half rotation could help pust that lever,.....i suggested to you an eccentric plate be attached to the tip of the shaft so that a half rotation or 1/4 rotation by a strong motor should be able to help push the lever.View attachment 66738

 

[kinarfi]

linear actuator and micro switches or as suggested use a servo with a cam to move the lever, if using servo, you can disable or remove the pwm board and directly power the motor via limit switches, but you may need an H bridge to back off the servo

 

[Robert Milton]

which way do you think would be the least costly?

 

[kinarfi]

I drew up a cam that would give you 0 at 90 degree, 10 mm at 0 degree and 20mm at 180 degree. Add 3 555 timers, one for each position and then you would power up only the 555 for each position you want.

 

[kinarfi]

which way do you think would be the least costly?

if you're asking me, I'd do the servo, servos are cheap, 555s are real cheap, but it may depend on how much force it take to move your lever. Making the cam may task you a bit.

 

[kinarfi]

Another idea for servos is a single arm with a connecting rod; 0 deg = 0, 45 deg = 10mm, & 90 deg = 20 mm

 

[jpanhalt]

Or, just buy a linear servo for less than $4 USD.

**broken link removed**

It is also quite easy to convert a regular servo with rotary motion to a linear servo. In fact, EMS used to sell a purpose-designed part that replaced the top case on a typical servo to give a liner motion. The range of motion was about 3 cm.

How much force do you need? How fast does it have to move?

John

 

[Robert Milton]

I am yet to find out how much force would be the right amount for the applications in question As for the desired speed to achieve the 2 settings [and plus back to beginning no-pressure mode], my guess would be that when the remote button is pressed calling for any of the 3 settings it should deliver immediately.