DC servo-motors

Transfer functions for system elements 4.4.1 DC servo-motors... 

Fig. 4.13 Simple DC servo-motor, where A h is the field eoil constant.

Fig. 4.14 DC servo-motor under armature control, e it) = Armature excitation voltage e it) = Backemf /a(t) = Armature current = Armature resistance = Armature inductance 6f = Constant field voltage if = Constant field current Tm = Torgue developed by motor 6 t) = Shaft angular displacement u] t) = Shaft angular velocity = dd/dt.

Figure 4.15 eombines equations (4.18), (4.20) and (4.22) in bloek diagram form. Under steady-state eonditions, the torque developed by the DC servo-motor is... 

Fig. 4.15 Block diagram representation of armature controlled DC servo-motor.

Under steady-state eonditions, the torque developed by the DC servo-motor is... 

Fig. 4.18 Steady-state relationship between ef(t) and o (t) for a field controlled DC servo-motor.

DC servo-motor. Field controlled, with transfer function as shown in Figure 4.17. It will be assumed that the field time constant LylRy is small compared with the dynamics of the machine table, and therefore can be ignored. Flence, DC servomotor gain (Nm/V). 

Micrometers are also useful positioning elements. Although manually operated micrometers are not suitable for most imaging applications, they provide an inexpensive way to acquire current-distance curves and perform substrate modifications (17,18). Submicron positioning is available with differential micrometers. Motorized micrometers are widely available, and micrometers with DC servo motor drives in closed-loop operation (see below) can give excellent results. 

Another consideration is the sizing of the mechanical backgauge to the press brake. The backgauge is usually driven to position by a precision ball screw coupled to a DC servo motor. Small brakes with up to 5 or 6 ft. between the side frames can be accommodated with a single-screw backgauge system. (See Fig. 18.) Travel front to rear is usually around 24 in., but 50 in. travel is available for larger applications. (See Figs. 19 and 20.)... 

FIGURE 35.3 The ARM Guide. The patient s arm is attached to a hand splint (S) that is attached to an orientable linear track. A dc servo motor (M) can assist in movement of the subject s arm in the reaching direction (R) along the linear track. Optical encoders record position in the reach (R), pitch (P), and yaw (Y) axes. A six-axis force sensor (F) records the forces and torques at the interface between the device and the subject. The device is statically counterbalanced with two counterbalance weights (C). 

Motor Two brushed DC servo motors Drive Differential drive Maximum Speed 1.7m/s Computing System... 

The Puma robot has six degrees of freedom and has six revolute links to deliver a tool or maintain a position at any point in the space.The point has to lie within the working envelope. The first three links make up the main structure of the robot. The rest make up the wrist, which usually holds the part to be carried (see Fig. 1). The links are powered by DC servo motors. The robot is controlled by a programmable microcomputer. ... 

The contact potential is found by applying an opposing potential until the null point is reached. It is essential that this potential is applied rapidly, in a time much smaller than the time constant of the circuit comprising the condenser and the external resistance. This is achieved by an integrating dc amplifier coupled to a servo motor which actuates a helipoi °. A reproducibility of 0.03 volts is claimed, with results in good agreement with other literature values. 

The DC motor is the classic variable speed drive. It is utilized as a universal main drive for capacities of up to several hundred kW and for servo drives down to the Watt range. 

P. Pillay and R. Krishnan. Application characteristics of pm synchronous and brushless dc motors for servo drives. IEEE Transactions on Industry Applications, 27(5) 986-996, 1991. 

A variety of devices are used to implement the power stage, depending on the actuator used to move the servo system. These range from small DC motors to larger AC motors and even more powerful hydraulic systems. This section will briefly discuss the power stage options for the smaller, electric driven servo systems. 

In contrast to the DC motors, which employ current switching and therefore perform poorly at low speeds, this closed-loop method of controlling stepping motors performs quite accurately even at very low velocities. On the other hand, the generation of the sinusoidally modulated input currents requires both accurate position measurement and separate current choppers for each phase. Thus the implementation cost is somewhat higher than a servo system utilizing DC motors. 

First, suppose the camera will be used in a surveillance application, to constantly pan back and forth across a store. For this apphcation, an actual servo system employing feedback is probably not necessary and would prove too costly. The required precision is fairly low, and low cost is of the utmost importance. Consequently, an open-loop stepping motor powered by transistors switching on or off will probably be adequate. Alternatively, even a DC motor operated in open loop, with microswitches to determine when to reverse direction will suffice. 

Now suppose the camera is used to visually inspect components as part of a robotic workcell. In this case, the requirements on precision are significantly higher. Consequently, a servo system using a geared DC motor and powered by a PWM voltage amplifier maybe an appropriate choice. If the robotic workcell is used extensively, a more reliable system may be in order. Then a brushless DC motor may be substituted for a higher initial cost. 

DC Motors-Speed Controb-Servo Systems, Electro-Craft Corp., Hopkins, Minn., 1972. 

A servo is a mechanical motorized device that can be instructed to move the output shaft attached to a servo wheel or arm to a specified position. Inside the servo box is a Direct Current (DC) motor mechanically linked to a positional feedback potentiometer, gearbox, electronic feedback control loop circuitry and motor drive electronic circuitry. 

One solution to transducer deflection is to eliminate it with a feedback control servo see Figure 8.2.5 (Franck, 1985a). The transducer is essentially a dc motor in which torque is measured by the current needed to prevent any deflection. No servo system is instantaneous, and a combination of high frequency and torque can lead to transducer compliance (Mackay and Halley, 1991). The upper frequency is about 100 rad/s, whereas stiff torsion bar systems have resonant frequencies above 10 rad/s and piezoelectric sys-... 

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