Download Torque‐Speed Measurements

TechNote44
April15,2014
Torque‐SpeedMeasurements
FLIR MCS pan‐tilt units (PTUs) have traditionally been specified in terms of payload weight. However, performance will vary greatly depending on payload configuration and balancing. A more precise way to determine system performance is to use dynamic torque. This technical note describes the MCS PTU torque‐speed measurements. It also discusses some of the implications on system design. Torque‐SpeedCurve
Torque
Torque‐speed curves show the amount of torque available at the payload over the operating speed range of the device. Figure 1 below shows a typical torque‐speed curve. Two distinct regions are seen. At lower speeds, the system delivers an approximately constant torque. This is because the drive electronics can get the correct amount of current into the motors. As the speed increases, so does the motor back electromotive force (EMF). EMF is a voltage generated by a rotating motor. The EMF will eventually become high enough that the drive electronics are unable to supply enough current to the motors. Less output torque is available, eventually reducing to no torque above a certain speed. Speed
Figure 1 Basic Torque‐Speed Curve MeasurementTechnique
Dynamic torque was measured using the system shown in Figure 2. The PTU is slowly accelerated to the desired speed. Brakes were used to gradually increase the load until the PTU could no longer rotate. A sensor measures the amount of torque being generated when the system stalls. Figure 2 FLIR MCS Torque Tester 1 of 8 All of the measurements were done at room temperature. Multiple data points were taken to ensure data integrity. Available torque will be slightly reduced at the colder and hotter temperatures due to the materials used to build the PTU. EffectsofPowerSupplyVoltage
Power supply voltage can have a significant effect on available torque. Earlier, it was discussed that torque reduces at higher speeds due to the back EMF of the motor. Figure 3 shows the effect for the D48E. All parameters were kept constant; only the supply was changed. 6
Torque (ft‐lbs)
5
4
3
30V Regular Power
2
12V Regular Power
1
0
0
20
40
60
80
100
120
Speed (deg/sec)
Figure 3 Torque for D48E Regular Pan Power Setting, 12V vs. 30V Suggestionsfor12VBatteryOperation
Many customers need to run off 12V ‘battery’ systems. Since lower torque is available, the acceleration values should be reduced to the lowest setting that still meets the system performance requirements. The maximum speed will also be reduced with a lower voltage. 12V batteries have an output range of approximately 10.5 VDC – 13.1 VDC. When determining what parameters to use, make sure to test with a battery is slightly discharged (but above the minimum PTU operating voltage of 12V) to ensure that the system will still operate correctly as the battery drains. EffectsofMotorPowerSetting
FLIR PTUs offer three different power settings: Low, Regular (default) and High. Low power reduces the motor current by 50%, while high power increases the motor current by 50%. Figure 4 shows how this affects output torque. Torque varies the same as the change in motor current at low speeds. That is, there is 50% more torque at high power than at regular power. The difference grows less as the speed increases due to the back EMF. Even with the highest power setting, the drive electronics can’t provide the requested motor current, reducing the available torque. 2 of 8 TechNote44
April15,2014
24
Torque (fl‐lbs)
20
16
30V Regular Power
12
8
30V Low Power
4
30V High Power
0
0
6
12
18
24
30
36
42
48
54
60
Speed (deg/sec)
Figure 4 D300 30V Pan Torque at Different Power Settings EffectsofStepMode
The selection of the step mode has an effect on available torque. Eighth‐stepping has slightly more torque at lower speeds. It also has the smoothest motion. At higher speeds, half‐step mode will have the most torque. FLIR pan‐tilts offer an auto‐step option. This setting will start the PTU out in eighth‐step mode at low speeds. It then switches to quarter‐step and finally half‐step at the speed increases, providing the PTU with the maximum possible output torque over the full operating range. The graphs provided at the end of the report used the best step mode at each speed. 6.00
Torque (Ft‐Lbs)
5.00
Half
Quarter
Eighth
4.00
3.00
2.00
1.00
0.00
0.00
20.00
40.00
60.00
80.00
100.00
120.00
Speed (deg/sec)
Figure 5 D48E Regular Pan Power with Different Step Modes 3 of 8 D48E‐SeriesProductFamily
The D48 E‐Series PTUs come in two different varieties: standard and continuous pan (slip ring). Both varieties have the same torque performance. D48 E‐Series Pan Axis Torque
8
7
Torque (ft‐lbs)
6
5
30V Regular Power
4
30V Low Power
3
30V High Power
2
12V Regular Power
1
0
0
20
40
60
80
100
120
Speed (deg/sec)
D48 E‐Series Tilt Axis Torque
9
8
Torque (ft‐lbs)
7
6
30V Regular Power
5
30V Low Power
4
30V High Power
3
12V Regular Power
12V High Power
2
1
0
0
5
10
15
20
25
30
35
Speed (deg/sec)
4 of 8 TechNote44
April15,2014
D100E‐SeriesProductFamily
StandardVersion
D100 E‐Series Axis Torque
10
9
Torque (ft‐lbs)
8
7
6
5
30V Regular Power
4
30V Low Power
3
30V High Power
2
1
0
0
20
40
60
80
100
120
140
Speed (deg/sec)
5 of 8 EXVersion
‐ TODO: Verify using correct combination of motors/gears D100 E‐Series EX Pan Axis Torque
25
Torque (ft‐lbs)
20
15
30V Regular Power
30V Low Power
10
30V High Power
12V Regular Power
5
0
0
10
20
30
40
50
60
70
Speed (deg/sec)
D100 E‐Series EX Tilt Axis Torque
35
30
Torque (ft‐lbs)
25
30V Regular Power
20
30V Low Power
15
30V High Power
10
12V Regular Power
12V High Power
5
0
0
10
20
30
40
50
60
70
Speed (deg/sec)
6 of 8 TechNote44
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D300E‐SeriesProductFamily
StandardVersion
D300 E‐Series Axis Torque
24
Torque (ft‐lbs)
20
16
30V Regular Power
30V Low Power
12
30V High Power
8
12V Regular Power
12V High Power
4
0
0
6
12
18
24
30
36
42
48
54
60
Speed (deg/sec)
EXVersion
D300 E‐Series EX Axis Torque
35
30
Torque (ft‐lbs)
25
20
30V Regular Power
15
30V Low Power
10
30V High Power
5
0
0
5
10
15
20
25
Speed (deg/sec)
7 of 8 High‐SpeedPanVersion
The High‐Speed Pan version of the product has a different gear combination in only the pan axis. The tilt axis is the same as the standard D300E. D300 E‐Series High‐Speed Pan Torque
18
16
Torque (ft‐lbs)
14
12
30V Regular Power
10
30V Low Power
8
30V High Power
6
12V Regular Power
4
12V High Power
2
0
0
20
40
60
80
100
Speed (deg/sec)
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