Baldor 23H Series Installation & Operating Manual page 125

Figure 1 represents a summary of vector and servo drive technology comparisons.
Figure 1.
Speed
Acceleration
Typical Motor
Response
Inertia
(lb.-in.-S )
2
Linear Drives
First of all, let's define a "linear" motor. Imagine that a rotary motor is cut open and unrolled. The
result is a flat linear motor. The same electromechanical principles apply whether the product is
rotary or linear. For example, a permanent magnet DC rotary motor is similar to a permanent
magnet linear motor; and an AC induction squirrel cage motor is similar to an induction linear
motor. The same electromagnetic force that produces "torque" in a rotary motor also produces
"force" in a linear motor. The linear motor utilizes the same controls and programmable position
controllers as rotary motors.
Some other similarities of rotary and linear: Rotary "torque" is measured in pound-feet (lb-ft) or
pound-inch (lb-in), or newton-meters (N-m); whereas linear "force" is measured in pounds (lb), or
newtons (N). Rotary "velocity" is measured in revolution per minute (rpm); whereas linear "veloci-
ty" is measured in inches per second (in/sec), or meters/second (m/sec). The "duty cycle" is the
same for both technologies; it is the time a motor receives power divided by the total cycle time.
Prior to the invention of linear motors, the only way to produce linear motion was to use either
pneumatic or hydraulic cylinders or to translate rotary motion into rotary motion using ball screws
or belts and pulleys. Sometimes for some applications, these other linear motion technologies may
be a better choice. But each application has to be investigated. As an example, Figure 2 represents a
comparison of linear motors vs. ball screws.
Figure 2.
Comparison of Linear Motors vs. Ball Screws
Linear Motors
Low to Medium Force
High Speed (to 200 ips)
High acceleration (to 10 g's)
Two parts with no contact
Lower maintenance
No backlash
Greater accuracy
Application Notes
DRIVE TECHNOLOGY COMPARISON
(1 HP AT 1800 RPM)
VECTOR
Traditional Traditional
Traditional
7.6" O. D.
Traditional
0.052
DC
SERVO
Std Inertia
Higher Speeds are possible
Fast Very Fast
4" O. D. 4.7" Sq.
Fast Very Fast
0.024 0.0078
Ball Screw
High Force
Low Speed (50 ips)
Lower acceleration (2 g's)
Many parts with contact wear point
Higher maintenance
Longer settling time
Lower accuracy
Page 5
BRUSHLESS SERVO
Low Inertia
Ultra Fast
3.5" Sq.
Ultra Fast
0.0025