X axis problem

[joethepro]

I'm looking for the simplest way to build a gantry that travels back and forth on the X axis only without it being hooked up to a computer. It will be belt driven and controlled by an 18v dc drill motor.

I was thinking about using an "on-off-on" switch at each end of the gantry slide to reverse the direction of the gantry, but I think the motor won't last long if I do that. I need something to slow the motor at each end before it reverses direction.

I've thought about Hall sensor's, 555 timers, limit switches etc., but they seem complicated being that I don't know much about them. Just want something simple.

Any idea's?

 

[picbits]

How accurate does it need to be ?

If not too accurate then you could use one switch to cut the motor at a certain point then another one slightly further down to reverse the motor (assuming the carriage has enough inertia to carry it).

Personally I'd use a stepper motor but I don't know your application.

 

[sowjoe]

How accurate does it need to be ?

If not too accurate then you could use one switch to cut the motor at a certain point then another one slightly further down to reverse the motor (assuming the carriage has enough inertia to carry it).

Personally I'd use a stepper motor but I don't know your application.

Doesn't have to be accurate at all.

I thought about using a switch to cut the motor at a certain point and using the inertia of the gantry to carry it to a reverse switch, don't know how well that would work.

Thanks

 

[picbits]

Or you could use the switch towards the end of the gantry to cut the motor then trigger the timer which then after "x" seconds triggers the reverse circuit. That way you don't need to worry about another switch at the end of the gantry - you could however have one as an emergency cutoff or something.

 

[sowjoe]

Or you could use the switch towards the end of the gantry to cut the motor then trigger the timer which then after "x" seconds triggers the reverse circuit. That way you don't need to worry about another switch at the end of the gantry - you could however have one as an emergency cutoff or something.

I wonder if the timer could control the whole thing?.... but I have to admit, I know nothing about 555 timers nor how to hook them up, hence the "simple" hook up. Maybe I should buck up and learn? Can you point me in the right direction?

 

[picbits]

Ok - I would start with relays - nice and simple.

I've had a couple of whiskys so I won't try and get too accurate but .......

You'd trigger a relay to latch - that would drive the motor one way. When the carriage gets to a certain point, it would pass a switch which would reset the relay cutting the power to the motor. It would also trigger a timer (555 or otherwise) which would introduce a delay before triggering the reverse latching relay.

When the carriage gets to the opposite side and triggers another limit switch towards the end of the carriage, the reverse relay would be cut, a different timer would activate for a preset time then the cycle would repeat again.

This way you're using natural friction of the carriage to slow it down without putting undue strain on the mechanisms. Moving the sense switches or increasing / decreasing the delay of the timer before reversing would be pretty simple to adjust if needed.

 

[sowjoe]

Ok - I would start with relays - nice and simple.

I've had a couple of whiskys so I won't try and get too accurate but .......

You'd trigger a relay to latch - that would drive the motor one way. When the carriage gets to a certain point, it would pass a switch which would reset the relay cutting the power to the motor. It would also trigger a timer (555 or otherwise) which would introduce a delay before triggering the reverse latching relay.

When the carriage gets to the opposite side and triggers another limit switch towards the end of the carriage, the reverse relay would be cut, a different timer would activate for a preset time then the cycle would repeat again.

This way you're using natural friction of the carriage to slow it down without putting undue strain on the mechanisms. Moving the sense switches or increasing / decreasing the delay of the timer before reversing would be pretty simple to adjust if needed.

Good idea. I could eliminate the 555 just by adjusting the locations of the switches....

Here's another question: If I were to do this all electronically (without the on-off-on switches) how would you build it?

 

[picbits]

Personally I'd use a PIC microcontroller, hall effect sensors or optical sensors (or reed switches and a magnet on the carriage), a few lines of code, a couple of relays and off we'd go. You could even have a sensor on the motor to count the number of revolutions assuming you don't have any slip on the rest of the mechanical system.

I do however have around 30 years experience in electronics and mechanical engineering so what might appear fairly trival to me could be quite complicated for others.

 

[Mr RB]

... This way you're using natural friction of the carriage to slow it down without putting undue strain on the mechanisms. Moving the sense switches or increasing / decreasing the delay of the timer before reversing would be pretty simple to adjust if needed.

Another way is to just use a reversing relay and 2 limit switches, and use a constant current limit on the PSU to the DC motor.

That CC will limit starting and reversing currents, ie; will give the gentle acceleration/decelerations needed on the polarity changes. You can dial in the reversing properties by adjusting the CC limit.

The limit switches will need to be the type that can be travelled past, as there will be a natural distance needed AFTER the switch, for the reversing operation.

 

[sowjoe]

Another way is to just use a reversing relay and 2 limit switches, and use a constant current limit on the PSU to the DC motor.

That CC will limit starting and reversing currents, ie; will give the gentle acceleration/decelerations needed on the polarity changes. You can dial in the reversing properties by adjusting the CC limit.

The limit switches will need to be the type that can be travelled past, as there will be a natural distance needed AFTER the switch, for the reversing operation.

This sounds like what I was looking for. I was looking for a way to gently accelerate/ decelerate the motor at the ends of the run without using a mechanical device. The problem is, I don't know what PSU and Constant Current limit is. I looked up what a reversing relay is and it seems pretty straight forward, but I can't find information on PSU and Constant Current limiters and how to hook them up.

Could you send me a diagram and/ or explain in more detail this seemingly simple design?

Thanks Mr. RB!

 

[Mr RB]

The PSU is a Power Supply Unit, that is just a common DC power supply that has enough voltage to make your motor move at the correct speed during the middle portion of the movement. You mentioned "an 18v drill motor" so an 18v DC power supply might be ok.

It would really help if we knew the motor voltage and amps when driving your load at the correct speed.

The "constant current" driver can be made yourself with a couple of transistors and a heatsink and a few resistors. It connects in series with the motor, and sets a max limit on the amount of current that will be allowed through the motor. You can google or wiki for "constant current circuit" and find lots of simple examples.

 

[sowjoe]

The gantry rails will be 48 inches long.

I think what I'm going to do is build a test model using one on-off-on switch. The 2nd on will reverse the polarity of the dc motor thereby reversing the direction of the carriage. Simple and easy.

If I have a problem with reverse-direction smoothness I could incorporate some type of soft-start motor controller too ....
**broken link removed**

Here is the belt drive design I want to use....

https://bell-everman.com/products/lin...elt-linear-sbl

Video.... https://bell-everman.com/products/lin...elt-linear-sbl

 

[ClydeCrashKop]

A level wind mechanism to guide cable onto a cable-receiving spool utilizing an endless chain with a drive pin to shuttle a cable-guiding carriage back and forth along the length of the spool. The drive mechanism powering the shuttle chain includes two chain sprocket assemblies

https://www.freepatentsonline.com/3583653.pdf