New Additions to an Old Favorite – New Fastact G-Series Servomotor

By Andrew Barrett, Product Line Manager for Industrial Servomotors

Fastact G Servomotors are known as the choice for highly dynamic servo applications where positioning times of 30 msec or less are often the norm. Moog continues to enhance this product line with additions such as the new Fastact G Size 1 motor that adds the 40 mm flange size to the existing product range and improvements such as expanded encoder feedback options.

In response to needs in the marketplace, Moog developed the G4-1, a low voltage (325V) servomotor that comes with the standard options such as a brake, encoder/resolver choices and various shaft options. All this flexibility comes with the exceptional performance as shown in table 1. Now The G-Series range goes from a size 1 (40 mm flange size) to a size 6 (190 mm flange size) with the following performance range:

• Continuous stall torques ranging from 0.15 [1.3] to 77 [681] Nm [lb.in],
• Peak Torques from 0.5 [4.4] to 240 [2124] Nm [lb.in] and
• Continuous power from 0.13 [0.18] to 12 [16] kW [hp].

Category	Symbol	G4-1			Units
Stack length (in mm)	-	L20	L40	L60	-
Nominal Torque, continuous duty, locked rotor	MO	0.15 [1.3]	0.27 [2.4]	0.37 [3.3]	Nm [lb.in]
Nominal speed	nN	9000	6000	6000	rpm
Max torque	Mmax	0.5 [4.4]	1 [8.9]	1.5 [13.3]	Nm [lb.in]
Nominal torque, continuous duty, nominal speed	MN	0.14 [1.2]	0.2 [2.1]	0.3 [2.7]	Nm [lb.in]
Output power, continuous duty, nominal speed	PN	0.13 [0.18]	0.15 [0.20]	0.19 [0.25]	kW [hp]
Rotor inertia (resolver included)	J	0.023 [0.2]	0.045 [0.4]	0.068 [0.6]	Kgcm2 [lb-in.sec2 x102]
Torque constant	kT	0.17 [1.5]	0.34 [3.0]	0.46 [4.1]	Nm/Arms [lb-in/Arms]
Thermal time constant	tTh	600	650	700	sec
Winding resistance at 25°C (phase to phase)	Rtt	23.0	34.8	37.0	Ohm
Weight (without brake)	m	0.55 [1.2]	0.68 [1.5]	0.82 [1.8]	Kg [lb]

Table 1 - Performance Specification for Standard Models

Notes:

1. Motor performances as measured with Moog's servodrive of proper size
2. Rotor inertia: with resolver, no holding brake

Performance Curves

Expanded Feedback Options for Greater Flexibility

With the growing requirements for encoder feedback in industrial markets, Moog is now offering various encoder feedback options on our high-performance Fastact G Servomotors. Our application experts work with customers to identify which technologies are the best for their applications.

Selecting Resolver or Encoder Based Systems

When the environment has hot, very cold, humid, oily, high vibration/shock, dusty or other beyond normal industrial conditions, a resolver-based system is the preferred choice.

When precise positioning, smooth torque and stable velocity control are top priorities for the application, the encoder-based system is the preferred choice. Encoders typically have all their electronics onboard, minimizing interconnections, but limiting operating temperatures.

In determining whether to use a Moog servomotor with a resolver or encoder, close consideration of the application under the characteristics shown in table 2 is required. All factors must be balanced for the right design fit.

Specifications: Encoders vs. Resolvers

Category	Resolver	Encoder
Angle measurement	Absolute	Absolute/Incremental
Absolute resolution	16 bits	13 bits
Incremental resolution	N/A	10,000 lines/revolution
Accuracy (arc minutes)	4 to 40	0.25 to 6
Electronic interface	R/D converter	Direct
Noise immunity	Sensitive	Best
Output signal	Analog	Analog/Digital
Construction materials	Robust	Fragile
Weight	Heavy	Lighter
Inertia	High	Low
Longevity	Very High	High
Shock/vibration	Rugged	Limited
Temperature Range	-50 ºC to +150 ºC	-20 ºC to +100 ºC
Contamination	Immune	Vulnerable

Table 2: Encoder v Resolver Application Considerations

Selecting Encoders

In determining which type of encoder to use, the initial choice is to determine whether to use an absolute or incremental encoder.

Incremental encoders have output signals that repeat over the full range of motion. It is important to understand that each mechanical position is not uniquely defined. When the incremental encoder is turned on, the position of an incremental encoder is not known since the output signals are not unique to any singular position.

Absolute encoders report absolute positional information. When powered up, it does not require a home cycle, even if the shaft was rotated while the power was off. If an absolute encoder is chosen, the further choice is whether to use a single-turn (unique position information within one revolution) or multi-turn (unique position information beyond one revolution) absolute encoders.

Table 3 below shows the encoder option sizes available by servomotor front flange sizing.

TYPE	MFG	Size 1(40 mm)	Size 2 + 3 (55 + 70 mm)	Size 4(100 mm)	Size 5 + 6(140+190 mm)
Incremental	STEGMANN	-	CKS 36	CNS 50	CNS 50
ABS Single Turn		-	SKS 36	SRS 50	SRS 50
ABS Multi Turn		-	SKM 36	SRM 50	SRM 50
Incremental	HEIDENHAIN	-	ERN 1185	ERN 1387	ERN 1387
ABS Single Turn		ECN 1113	ECN 1113	ECN 1113	ECN 1313
ABS Mutli Turn		EQN 1125	EQN 1125	EQN 1325	EQN 1325

Table 3. Encoder options by servomotor flange size

About the Author

Andrew Barrett, B.E.(electrical), M.Eng.Sc. (control electronics), MBA, is a Product Line Manager for Moog’s Industrial Servomotors. He brings 15 years of experience in engineering, operations and product line management, gained during a career with several multinational companies.

© 2008 Moog Inc. All rights reserved.