Machine Repair Project needs helpful ideas

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Machine Doctor 13

Joined Jul 13, 2019
11
I want to replace an antiquated stepper relay with something more modern. The stepper relay is being used on an older Mazak turret lathe to provide feedback to the CNC control as to what tool station is currently being used.

The CNC control reads the part program information and when a tool change is called for the CNC sends a signal to a solenoid to index the tool turret to one of 8 tool stations. At the same time the CNC sends a +24 VDC signal to the stepper relay coil to advance the wiper to one of the 8 output contacts
(each output contact represents one of the 8 tools). The stepper relay is worn out and I want to replace it with something like a multiplexer or counter.

So basically, I want to come up with a circuit that uses one input to select 1 of 8 outputs and has to remember the last output when power is removed and then turned on again. Any good ideas will be greatly appreciated.
 

drc_567

Joined Dec 29, 2008
714
... Just trying to get a little better understanding of the details.
When the CNC sends a 24 VDC signal to the original stepper relay, the stepper relay advances one position at a time until it reaches the correct output contact for a specific tool. How does the stepper know which position or tool is required? The CNC would have to tell the stepper to rotate a certain number of steps from a home or base position. It seems like one idea would be to translate the CNC's tool position increment into binary, which could then be used as an address input to a 3 to 8 multiplexor FET driver of one sort or another. The CNC still has to receive a signal confirming which tool is active. As long as the 3 bit address to the multiplexor is unchanged, ... just maintaining logic level power, a main power restart should keep the same tool active.
 

Thread Starter

Machine Doctor 13

Joined Jul 13, 2019
11
... Just trying to get a little better understanding of the details.
When the CNC sends a 24 VDC signal to the original stepper relay, the stepper relay advances one position at a time until it reaches the correct output contact for a specific tool. How does the stepper know which position or tool is required? The CNC would have to tell the stepper to rotate a certain number of steps from a home or base position. It seems like one idea would be to translate the CNC's tool position increment into binary, which could then be used as an address input to a 3 to 8 multiplexor FET driver of one sort or another. The CNC still has to receive a signal confirming which tool is active. As long as the 3 bit address to the multiplexor is unchanged, ... just maintaining logic level power, a main power restart should keep the same tool active.
The stepper relay advances to the next output contact each time the CNC sends a turret index command (a 2 second +24V signal to the stepper relay coil). So if the Tool #2 is finished with it's operation, and the CNC wants to call up Tool #5 for the next operation, the CNC will send 3 separate 2 second signals to the stepper relay with the stepper relay advancing each time (in this case three contacts away from the Tool #2 contact). So the stepper relay doesn't really know what tool station is currently active. It merely reacts to the command signals from the CNC.
 

MaxHeadRoom

Joined Jul 18, 2013
19,042
Are you familiar with PLC' programming?
Some kind of external logic is required to do it neatly and "modern".
Unless going back to a mechanical solution.
Max.
 

drc_567

Joined Dec 29, 2008
714
... Is it possible to modify the CNC program in a manner such that after one tool has been used, the stepper increment returns to the 0 position? The goal is to have the command for the next immediate tool generate a positive, absolute number of 24 VDC pulses that are descriptive of the next tool to be used. This modified number of pulses would be used to increment an 8 bit binary counter, yielding a 3 bit digital address that could be used as input to a multi-plexor chip. Say your program required the #5 tool, then 5 pulses, suitably reduced to +5 volts, would increment the 8 bit counter 5 times, giving an address of '101'. The mux would then activate output pin #5.
... Is there any merit to this line of thinking, or is something else necessary?
A picture might contribute to understanding what is involved.
 
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MaxHeadRoom

Joined Jul 18, 2013
19,042
It is very difficult to get into Mazak (mits) control in order to modify, the usual way often done is to use a small external PLC to control the T.C.
Max.
 

Thread Starter

Machine Doctor 13

Joined Jul 13, 2019
11
... Is it possible to modify the CNC program in a manner such that after one tool has been used, the stepper increment returns to the 0 position? The goal is to have the command for the next immediate tool generate a positive, absolute number of 24 VDC pulses that are descriptive of the next tool to be used. This modified number of pulses would be used to increment an 8 bit binary counter, yielding a 3 bit digital address that could be used as input to a multi-plexor chip. Say your program required the #5 tool, then 5 pulses, suitably reduced to +5 volts, would increment the 8 bit counter 5 times, giving an address of '101'. The mux would then activate output pin #5.
... Is there any merit to this line of thinking, or is something else necessary?
A picture might contribute to understanding what is involved.
I am looking at a 4017 Decade Counter. This just might work.
 

Dodgydave

Joined Jun 22, 2012
8,389
I'm looking at a 4017 Decade Counter. This might work.
If you want to use this chip, you need to set it to count to 8, then every time you give it a pulse, it will clock through 1-2-3...-8-1 etc... you could feed the clock pin with the command, and use it's outputs to feed slave relays to the tool heads.

Is there any feedback to tell the Cnc when it's at number 1 tool?
 

Thread Starter

Machine Doctor 13

Joined Jul 13, 2019
11
Can you explain exactly what a "stepper relay" is? Never heard of that term.

Don't you already have a thread about this? Using a new name for the same problem?
Yes, I have another thread on this. Just wanted to update because I wanted feedback on the decade/ counter circuit. A stepper relay is an old telephone company relay with a coil and an input and multiple outputs. Every time a voltage is sent to energize the coil the input (connected to a wiper) moves to the next output.
 
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