Selecting a Servomotor for an Application
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When you must select a servomotor for initial installation or for a replacement, you will need to consider the following data, which are shown in the table in Fig. 11-95. The first point to consider is whether the motor will be used for continuous duty or intermittent duty. The table shows the amount of continuous stall torque each motor can produce. The second rating from the table is the amount of peak torque. Both the continuous torque and the peak torque are listed in ounce-inches (oz-in.), pound-inches (Ib-in.), or inch-pound (in-lb.), and in newton-meters (N·m).The conversion of ounce-inches, pound-inches, and newton-meters follows:
1 lb-in. = 16 oz-in.
1 lb-in. = 0.112085 N·m
The rated power for each motor is listed in horsepower (hp) and kilowatts (kW). The calculation for determining horsepower and the conversion from horsepower to watts follows.
Horsepower = (torque x speed)/16,800
Torque = oz-in.
Speed = revolutions per second
The horsepower calculation uses the torque available at the specified speed.
1 hp = 746 Watts
The rated speed is listed on the data table as rpm (revolutions per minute). The rated current is listed in A rms. The peak current and the maximum continuous AC input power are listed in A rms. The rotor inertia is rated in oz-in.2 (mass). The model numbers for each motor are listed across the top of this table.
Technical Data | Z-605 ZX-605 ZXF-605 | Z-606 ZX-606 ZXF-606 | Z-610 ZX-610 ZXF-610 | Z-620 ZX-620 ZXF-620 | Z-630 2X-630 ZXF-630 | Z-635 ZX-635 ZXF-635 | Z-640 ZX-640 ZXF-640 | Z-910 ZX-910 ZXF-910 | Z-920 ZX-920 ZXF-920 | Z-930 ZX-930 ZXF-930 | Z-940 ZX-940 ZXF-940 | |
Continuous stall torque | oz-in Ib-in Nm | 346 22 2.44 | 633 40 4.47 | 867 54 6.12 | 1,743 109 12.31 | 2,475 155 17.48 | 2,475 155 17.48 | 4,114 257 29,05 | 2,407 150 17.0 | 4,263 266 30.1 | 5,990 374 42.3 | 9,021 564 63.7 |
Peak torque | oz-in Ib-in Nm | 1,083 68 7.65 | 1,954 122 13.80 | 1,733 108 12.24 | 3,486 218 24.62 | 4,951 309 34.96 | 4,951 309 34.96 | 8,228 514 58.10 | 5,205 325 35.4 | 8,525 533 61.5 | 11,980 749 84.6 | 18,041 1,128 127.5 |
Rated power | hp k Watts | 2 1.49 | 2.1 1.57 | 4.2 3.13 | 5.6 4.18 | 5.4 4.03 | 6.1 4.5 | 5.9 4.40 | 9.6 7.2 | 10.4 7.8 | 11.0 8.2 | 11.1 8.3 |
Rated speed | rpm rps | 6,200 103 | 3,600 60 | 7,000 117 | 3,700 62 | 2,500 42 | 3,000 50 | 1,600 27 | 5,000 83.3 | 3,150 52.5 | 2,300 38.3 | 1.500 25.0 |
Rated current [line) | A (rms) | 5 | 5.3 | 14.1 | 14.1 | 14.1 | 14.1 | 14.1 | 27.2 | 27.7 | 28.3 | 28.3 |
Peak current (3.3 sec max) | A (rms) | 16.6 | 17.2 | 28.2 | 28.2 | 28.2 | 28.2 | 28.2 | 56.6 | 56.6 | 56.6 | 56.6 |
Max cont AC A (rms) input power (3 phase 240 VAC) | A (rms) | 6 | 6 | 15 | 15 | 15 | 15 | 15 | 30 | 30 | 30 | 30 |
Rotor inertia | oz-in2 (mass) oz-in-sec2 kgm'xlO6 | 5.45 0.01 99.6 | 9.45 0.02 172,9 | 13.73 0.04 251.2 | 35.87 0.09 656 | 50.79 0.13 929 | 56.21 0.15 1,028 | 111.21 0.29 2,034 | 50.79 0.132 929 | 111.21 0.288 2,034 | 166.21 0.431 3,040 | 459.48 1.190 8,404 |
Motor weight | Ibs kg | 10.0 4.5 | 14.0 6.4 | 17.0 7.7 | 29.0 13.2 | 32.0 14.5 | 37 16.8 | 51.0 23.2 | 32.0 15.0 | 57.0 26.0 | 65.0 29.0 | 112.0 51.0 |
Shipping weight | Ibs kg | 52.0 23.6 | 55.0 25.0 | 56.0 26.4 | 71.0 32.3 | 74.0 33.6 | 79.0 35.9 | 93.0 42.3 | 89.0 40.0 | 114.0 52.0 | 122.0 55.0 | 169.0 77.0 |
FIGURE 11-95 Technical data table for selecting servomotors. The motors are listed across the top of the table and the data are listed down the side. (Courtesy of Parker Compumotor Division.)
Problem 11-9
Select the proper motor from the table shown in Fig. 11-95. The load for the motor is 6 hp, the rated speed is 3000 rpm, and the rated torque required for the load is at least 4500 oz-in.
Solution
Since the load requires a minimum of 6 hp and requires at least 4500 oz-in. of torque, the Z-635, ZX-635, or ZFX-635 should be the smallest motor selected. The motor could be the next larger size, but it is not advisable to select too large a motor.
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