Kirk,
You are correct, This actually done with with a cam. The turret
reaches position and then reverses direction for 50ms. This allows a
solonoid fired locking pin to disengage. The pin is used to locate the
turret on position while the curvic coupling is engaged to lock it in
position. The squence goes like this......
1. Unclamp the turret and engage the motor starter for
say clockwise rotation
2. When the turret is in between the called tool and the
position before it, engaged the locking pin and let it ride on the cam ring.
3. When the turret reaches the called tool, the locking
pin drops into the cam ring slot to stop the turret.
A proximity switch is used to confirm this has
happened. Clockwise starter disengages.
4. Counter clockwise motor starter is engaged for 50ms
to allow the locking pin to retract and the indexing pin to engage in its
hole. Proxy switches are used to confirm both has happened.
5. The motor counter clockwise starter disengages, the
motor brake is applied, then the turret clamps into to the coupling and the
index pin is retracted.
6. The tool position is reported to the CNC software and
the proper tool offset is called up.
7. Cycle complete.
As the turret rotates a 200ms timer is used between each tool position to
drop out the motor if a collision occurs during rotation. The timer is reset
while passing each tool position during rotation. Most electric turrets have
a thermal cut out on the motor to protect it from being damaged if a
collision occurs. There are 6 bits on the encoder...
TPS 1,2,3,4,Parity and Strobe the first 4 are positional Bits,
Parity is used to confirm The first 4 bits are correct and strobe is fired
once per tool position.....
Dave
----- Original Message -----
From: "Kirk Wallace" <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Sent: Friday, March 07, 2008 10:53 PM
Subject: Re: [Emc-users] Powerdex Tool Changers
> On Fri, 2008-03-07 at 20:50 -0500, Dave Keeton wrote:
>> Our Mazak Lathe has a turret that uses a belville spring washers in a
>> friction brake. The nice thing about it is that when a collision occurs
>> the
>> turret is pretty easy to get back on centerline. It uses a shot pin to
>> locate that is pulled back out when it is clamped. It is hydraulic
>> though.....It has live tooling also.....we never use the live tooling
>> except
>> tapping every so often...... If you use pins to locate and hold the tool
>> drum in place it is more difficult to align after collision.....I am not
>> to
>> sure about the disc brake idea.....Seems like tool pressure might make it
>> slip....could be dangerous in a power failure also......
>>
>> Dave
>
> So is the turret located by engaging a pin, setting a brake and then
> retracting the pin so that only the brake friction holds the turret
> position during machining? I assumed that with a tool crash that you
> would either break the tool, holder or turret.
>
> Rumor has it that a small lathe tool changer is available from Emco
> which can be seen at the bottom of the page here:
>
> http://www.emco.co.uk/pct55.htm
>
> I hear that it has a pawl on the turret drive shaft. The turret motor
> drives the turret until the pawl falls into the location for the desired
> tool. It then reverses against the pawl to lock it, take out all slop
> and get the final position. The turret rotates in a direction such that
> the cutting forces are also against the pawl, but apparently the pawl
> can flex under heavy cuts. This design has the advantage of being very
> simple, maybe even elegant.
> --
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/
> Hardinge HNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending)
>
>
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