Tol-O-Matic System Compatibility - Industrial and Bearing Supplies

ENGINEERING RESOURCES
SIZING AND SELECTION LIMITING FACTORS
Torque Margin
The following torque margins are recommended:
Stepper = 2.0
Brushless Servo = 1.15
Brushed DC Servo = 1.15
Inertia Match
For best efficiency and dynamic performance:
1≤
J REF
J MOTOR
≤10
Critical Speed
Critical speed for a given length of a given diameter screw in a
given bearing system is that rotational speed at which the screw
will have a natural frequency of oscillation about its own axis.
Curves of critical speed versus length are provided for each screw
diameter in the screw drive actuator section of this catalog.
Screw/Nut Thrust Capacity
Screw nut thrust capacity is the axial load which the screw and nut
can deliver to the carrier. This force is limited by the interaction of
the screw and nut threads for a solid nut and by the rolling
ball/thread system of the ball screw/nut. In the Tol-O-Matic actuator
design, all axial load is supported by the screw in tension
against the thrust bearings.
For solid nut actuators, maximum thrust and speed ratings are
shown on the critical speed charts. Because of thermal considerations,
the axial thrust to be provided by a solid nut at any operating
speed must be limited such that:
Thrust
Speed
X ≤ 0.1
Max. Thrust Rating Max. Speed Rating
Belt Rating
For belt actuators, the required thrust must be less than the belt rating
at the operating speed. These limits are shown in the belt actuator
section of this catalog.
Backlash
Defined as the linear distance which is lost in positioning the nut
when the screw direction of rotation changes. Backlash is directly
related to the closeness of fit between the nut and screw.
SOLID
BALL
NUT
Anti-
Low
Single
Single
Backlash
Backlash
Backlash (in.) 0.007 0.003 0.015 0.002
Backlash (mm) 0.18 0.08 0.25 0.05
Designation SN SNA BN BNL
RMS Torque
The RMS torque must be less than the motor’s continuous torque
rating.
SPEED
t 1
t 2
t 3
t 4
t 5
Torques are: T1,T2, T3, T4, T5
RMS Torque =
TIME
+ + + +
+ + + +
Higher ratios can be used if the duty cycle is modest. Consult the
factory for guidance.
For ball screw/nut actuators, the thrust ratings shown on the critical
speed charts represent the thrust at which a screw/nut life of 10 6
inches (25 x 10 6 millimeters) can be expected. For other loads, life is
given by:
( )
10
Rated Thrust
3
Life = X 10 6 inches
Nut Load Thrust
148