124 Industrial Robotics Fundamentals Copyright Goodheart-Willcox Co., Inc. The detector is part of a sensing system that responds to energy from the r source and outputs a signal that is used to control the load device. In some sens- ing systems, the load may be controlled directly by light-source energy. In other systems, the light energy must first be detected and amplified. fi There are even fi applications in which the detector itself serves as the load. Sensing system control may be achieved by interrupting a light beam between the source and detector. Other control methods may alter the intensity, focus, shape, or wavelength of the light source. The detector’s sensitivity can be adjusted to adapt it to specifi operating conditions. fic A common application of light-sensing systems in industrial processes is a counter (detector) on a conveyor line. An example may be a conveyor line that transports boxes from a packing area to a storage area. A light source can be placed along the conveyor line and aimed at the counter. As each box passes the light beam, the detector (counting device) adds another box to the count. Control is accomplished by breaking the light beam between the source and detector to count the number of boxes passing along the conveyor line. 6.3.2 Timing Systems Timing systems turn a device on or off at a specifi time or in step with an operat- fic ing sequence. Types of timing systems include delay timing, interval timing, and cycle timing. Delay timing systems provide a lapse in time before the load device becomes energized. Interval timing systems are used after a load has been ener- gized and operate using specifi time periods. For example, an interval timing fied system may be set to allow the load to remain energized only for a certain period. Cycle timing systems are typically more complex and may include both interval and delay timing to provide energizing action in an operational sequence. Timing systems also include thermal devices, motor-driven mechanisms, or other mechanical, electrical, or electrochemical devices. Hydraulic, pneumatic, mechanical, heat, and electrical energy sources may be used in various combina- tions to power timing systems. A type of timing operation is accomplished by a microprocessor in a computer. A microprocessor continually receives instruc- tions, executes them, and continues to operate in a cyclic pattern. All actions occur at a precisely defi time interval. An orderly sequence of operations, such as fined this one, requires a type of precision timing system. 6.3.3 Control Systems Control of an automated manufacturing system can be caused by input from an operator (person). It can also occur automatically due to a physical change. Dur- ing production, control systems are continually at work making adjustments that alter machine operations. The complexity of an operation determines the number of control functions needed. In many cases, several control components are used in various parts of the system. The control unit of an industrial robot determines its fl exibility and efficiency.fi fl Some robots have only mechanical stops on each axis. Others have microprocessor (computer) control with memory to store position and sequence data. Some impor- tant factors in the selection of a control unit are speed of operation, repeatability, accuracy of positioning, and the speed and ease of reprogramming. Non-servo, or open-loop, control systems are the most basic. They use sequencers and mechanical stops to control the end point positions of the robot