Abstract
Backlash, also known as mechanical play, is a piecewise differentiable nonlinearity which exists in several actuated systems, comprising, e.g., rack-and-pinion drives, shaft couplings, toothed gears, and other machine elements. Generally, the backlash is nested between the moving parts of a complex dynamic system, which handicaps its proper detection and identification. A classical example is the two-mass system which can approximate numerous mechanisms connected by a shaft (or link) with relatively high stiffness and backlash in series. Information about the presence and extent of the backlash is seldom exactly known and is rather conditional upon factors such as wear, fatigue, and incipient failures in the components. This paper proposes a novel backlash identification method using one-side sensing of a two-mass system. The method is based on the delayed relay operator in feedback that allows stable and controllable limit cycles to be induced and operated within the (unknown) backlash gap. The system model, with structural transformations required for the one-side backlash measurements, is given, along with the analysis of the delayed relay in velocity feedback. Experimental evaluations are shown for a two-inertia motor bench that has coupling with backlash gap of about 1 deg.
Highlights
Mechanical backlash, i.e., the phenomenon of play between adjacent movable parts, is well known and causes rather disturbing side-effects such as lost motion, undesired limit cycles in a closed control loop, reduction of the apparent natural frequencies and other
For a review of this phenomenon we refer to [1]. It is the progressive wear and fatigue-related cracks in mechanical structures that can develop over the operation time of an actuated system with backlash; this is in addition to appearance of a parasitic noise
Information about the presence and extent of backlash, which is a rather undesirable structural element, is seldom exactly known, and usually requires identification under regular operational conditions, i.e. during exploitation. When both the motor-side and load-side of a two-mass system are equipped with high-resolution position sensors, see for instance [14], the identification of backlash becomes a trivial task which can be accomplished under various quasi-static, low-excitation conditions
Summary
ASME Paper Title: Backlash Identification in Two-Mass Systems by Delayed Relay Feedback. The connecting elements contain a finite gap, here denoted by 2β, usually of a small size comparing to the rated relative displacement of the motion system. Within this gap, both moving masses become decoupled from each other. It is important to note that this structure has a backlash in feedback which differs significantly from feedthrough systems where a static backlash element appears either in the input or output channel Those types of systems with backlash have attracted considerable attention in systems analysis and control, see, e.g., [4], [5]. Some previous studies which consider analysis and control of backlash feedback systems can be found in, e.g., [6,7,8]
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