CNC_0002

MAKE: Workbench - Y-axis - Assembly

Preliminary Considerations:

The smaller linear positioning table ~ CNC 0014 [404XR - 200mm travel] (This is the alternative) will have enough travel to wind spar, wind torque tube, cut cores and mill carbon bars. It does not have enough travel to machine male or female full blade molds without doing the leading portion and the trailing portion separately.

Mach3 says 25,000, 35,000, and 45,000 unit/sec.

Recommended minimum possible move distance is 0.0001", which is 0.000254 cm, which is 0.00254 mm.

Using a pitch of 5 mm means that the rotation for a linear movement of 0.00254 mm is 5 / 0.00254 = 1968.5 increment (i.e. 2000 pulses per revolution encoder)

Desired maximum jog speed = 0.25 m/s = 250 mm/s. This is 250 / 5 = 50 rps

50 rps * 2,000 pulses per revolution = 100,000 pulses per second

25,000 unit/sec / 50 rps requires an encoder with 500+ pulses per revolution.

The maximum motor speed (Continuous: - No-load: - Full Speed) of a motor that is direct-coupled to the screw is 50 rps = 3,000 rpm

Or in other words; at 25.000 units/sec * 0.00254 mm = 63. 5 mm / sec 2.5" per sec at recommended minimum possible move distance.

Or; at 45.000 units/sec * 0.00254 mm = 63. 5 mm / sec 4.5" per sec at recommended minimum possible move distance,

It appears that the minimum possible move distance must be increase, or maximum jog speed reduced, or some combination of the two.

I think that the following does not provide any headroom. Perhaps headroom is only need while the motor is in the 'rated state.

Considerations re use of larger linear positioning table ~ CNC 0013 The NEMA 34 Reliance Electric Servo Motor E643 weights 10 lbs. The smaller NEMA 26 Reliance electric E242 and the planetary reduction will weigh about 5 lbs.

Linear Positioning Table #1473 could initially be used and then later #1472 could be substituted, to get a longer movement. The #1473 has a standard NEMA 34 motor mount, and this table is going to need a motor wherever it is used.

Initial Perceived Requirements:

Minimum Possible Move Distance = 0.00025" = 0.00635 mm. ~ "This sets the absolute limit to the accuracy of the work done on the Y-axis." ~ from Mack3Mill, section 4.5.2. I believe that this means that the 'steps per unit' is 4,000, with the unit being inches. ~ see; Mack3Mill, section 5.5.1.4. Note that the Parker 404 XE bi-directional repeatability is +/- 20 microns = +/- 0.02 mm.

Maximum Jog Speed = 0.25 meter/sec. = 590 ipm. Ref. Maximum Parker 0.36 meter/sec. Should this slower, but still faster than the Max Cutting Speed.

Maximum Cutting Speed = 0.05 meter/sec. = 120 ipm. Should this be faster, particularly for foam cores? Perhaps 'head-room' comes from the speed between cutting and jogging?

Force = 200 guestimate N (newton), 720 guestimate ozf (pound-force). For cutting and acceleration.

Acceleration: = ?

Note that the alternate linear positioning table (Item1472) has 4 times the movement for 1 revolution. However the planetary reduction, which should couple to it has a 5:1 ratio.

See note on OTHER: CNC Workstation - Workbench - Layout & Overview for total travel distance and motor.

______________________

A short answer from arvidb on CNCzone;- "For a smaller wood and plastic cutting machine (and maybe - maybe! some light aluminum), several people on CNCzone seam to have had success with 100-200 oz-in (0.7 - 1.4 Nm) stepper motors direct driving a 5 turns/inch (5 mm lead) ACME (trapezoidal) screw.

Purchased Items:

Linear Positioning Table ~ Item # CNC 0013: This is the one for the y-axis.

404XR, Table Travel: 400 mm. (15.75")

This might be ideal for a second winder for rotorhubs etc.; because it is fast and has large travel.

Linear Positioning Table ~ Item # CNC 0014: Alternative

404XR, Table Travel: 200 mm. (7.9")

Consider using this one for the Y-axis. It has a 5 mm drive screw, for a slower speed without additional reduction. It also has a usable motor mount flange.

Consider interchanging the motor mounts between # 1473 and # 1474, since this may shift the weight slightly toward the track and thereby decreasing the moment arm. Maybe it won't decrease the moment arm. It might increase it.

Servomotor c/w Encoder ~ Item # CNC 0017

Gearcase - Planetary - 5:1 ratio ~ Item # CNC 0019

Calculations:

The following is based on; the Mach3 manual, section 5.5.
The following is based on 'What motor, screw and gearing should I chose?' by arvidb on CNCzone.

Screw:

Metric screw lead (s) of 0.005 m is 5 mm / revolution.

Rotational jog speed = 0.25 m / 0.005 m = 50 revolutions / second. The maximum allowable screw speed is 60 rps

Reduction Ratio:

Secondary reduction of 1:1 (direct coupling between motor and screw) results in a motor speed of 50 rps * 1 = 50 rps = 3,000 rpm. The actual value, which is currently 3,000, should optimally be the rated speed of the chosen motor. Note that when cutting the speed is lower the torque will be the same even though the power is less.

Catch-up is described in article of which I have hard copy. Perhaps this 'head-room' comes from the speed between cutting and jogging?

Acceleration and Deceleration:

Not done yet. If the travel speeds are not exceptionally fast then the acceleration and deceleration should not be a concern.

Motor:

Power Required:

Screw Efficiency = Ball screw (η) = 0.9

Torque (Q) at the Screw = Force * (Screw lead / (2 * 3.1428)) * (1 / Screw efficiency (η))

= 200 N * (0.005 m / (2 * 3.1428)) * (1 / 0.9 [ball screw])

= 0.17677 Nm

Torque (Q) at the Motor = Torque at the Screw / Reduction Ratio

= 0.17677 Nm / 1 (secondary reduction) = 0.17677 Nm

Power Output (P) [in CNC context] = Force * Speed, Torque * Rotational speed, or voltage * Current

= 0.17677 Nm * (3000 rpm / 60) * 2 * pi = 55.6 W = (55.6 / 735) = 0.076 hp

For friction (transmission, ??) and motor loss 10% etc. increase by 50% = 83.4 W = (83.4 / 735) = 0.113 hp

Encoder:

The screw lead is 5 mm / revolution. 1" = 25.4 mm. Therefore I" of travel is 25.4 mm / 5 mm = 5.08 revolutions of the screw.

The secondary reduction is 1:1. Therefore 1" of travel is 5.08 * 1 = 5.08 revolutions of the motor.

The 0.0001" minimum move distance of will be 5.08 * 0.0001 = 0.000508 of a revolution, which is 1 / 0.000508 = 1 / 1968.5th of a revolution of the motor's shaft.

The rotation of the motor must be broken down into 1968.5 segments. Therefore an encoder with greater than 500 * 4(quadrature) = 2,000 PPR (Pulses Per Revolution) resolution will be needed. This is the maximum for the Renco RM15 and well within the US Digital E2.

Related Miscellaneous Note:

The controller must generate 3.000 RPM * 2000 PPR / (60 sec / min) = 100,000 pulses per second. On a 1GHz PC, Mach3 can generate 35,000 pulses per second. On a faster PC, Mach3 can generate 45,000 pulses per second. (see Mach3, section 5.2.2).

The Gecko G320 and G 340 have a 25 kHz PWM frequency.

The Gecko G320 and G 340 have a 250 kHz maximum step rate.

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Last Revised: January 6, 2007