Motorized positioners

Within a regular scanning electrochemical microscopy (SECM) system, the probe microelectrode, called the tip electrode, can be precisely positioned several micrometers away from a substrate under the control of a three-dimensional motorized positioner in the solution containing redox-active species. By scanning the SECM tip within the plane paralleling a substrate surface and simultaneously monitoring tip current (/ [ ), which is sensitive to the presence of conducting and... 

Most SECM experiments use tips with 1-25 /xm diameters. Thus, a positioner for these probes should be able to scan regions of 100-1000 /xm square at scan rates up to 50 /xm/s. For these conditions, motorized positioners are suitable. With smaller probes, the greater accuracy of piezoelectric tube or tripod positioners of the type found in STM and AFM instruments is required. 

The tip is first brought near to the sample via a coarse Z positioner, such as a controlled approach piezo-electric motor. This provides a 10 A step size and so is capable of very precise and controlled movement. As soon as a tunnelling current is detected, the tip is stopped and the fine control system is operated. Thus the lip is mounted on the end of a hollow, cylindrical piezo crystal, a tube scanner (a piezo-electric crystal can be made to deform under the influence of a voltage applied across it). The tube scanner has four strip electrodes on the outside, providing movement in the x and y directions (lateral movement), and one electrode covering the whole of the inside. A... 

Rocket Launcher and Rocket Motor Model 10 (p 172) was designed to propel the 60-kg aircraft bomb out of an inclined trough. The launcher was constructed of wood and metal with legs made of iron pikes. The launcher channel was a right angle wooden trough, ca 20 ft long with a motor and bomb positioner... 

Valve actuators may be classified broadly as directional, such as solenoids and electric motors force-balanced, such as spring-loaded diaphragms, and position-balanced, such as valve positioners. On the basis of this classification, Close (C7) describes the important types of... 

The model 900 SECM (CH Instruments) is the first commercial instrument specifically designed for SECM. Although STM instruments equipped with electrochemical accessories can be adapted for some SECM experiments, they cannot replace a general purpose SECM instrument. This section will describe the features of the model 900. The model 900 includes the cell and probe positioner illustrated in Figure 5 as well as a computer, motor controller, and bipotentiostat (35). 

Fig. 28.5. Robot for percutaneous needle puncture procedures (PAKY-RCM system). The lower joints are positioned and locked manually, while the upper stages are motorized. The needle positioner at the tip is transparent to X-rays to enable radiographic guidance. [Reproduced from Stoianovici et al. (1998) with permission]...

Piezoelectric and electrostrictive devices have become key components in smart actuator systems such as precision positioners, miniature ultrasonic motors and adaptive mechanical dampers. This section reviews the developments of piezoelectric and related ceramic actuators with particular focus on the improvement of actuator materials, device designs and applications of the actuators. 

A positioner is used to close the loop around a valve motor. It drives the motor until a mechanical measurement of stem position is balanced against its input signal. In this way, forces that would act to impede the motion of the stem are overcome. A positioner is essentially a high-gain proportional controller closing the loop around what is essentially single capacity plus hysteresis. 

High pressure drop across the seat of a control valve acts against the area of the seat in opposing the force of the valve motor. It can easily be sufficient to keep the valve from closing tightly. A positioner will place as much pressure on the valve motor as is available if the stem is very far from its directed position and so is able to overcome this difficulty. 

As was touched on previously, lamp maintenance will necessarily disturb the position of lamps which must be put right again. It has been suggested that the lamps could be mounted on small, motorized micro positioners, but again the control and capital cost of implementing this on large arrays may not be practicable. 

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