Unit 2: Mechanical Elements of Robotics - Practice Quiz

1 What is a robot link?

2 Which type of joint allows rotation about an axis?

3 What is a kinematic chain?

4 In a robot, what does an open kinematic chain have?

5 What is the main purpose of a mechanical transmission system in a robot?

6 Which device is commonly used to transmit rotary motion between shafts?

7 What is a gear train?

8 When a small gear drives a larger gear, what usually happens to the output speed?

9 Which component is used with a belt drive?

10 Which component is commonly used with a chain drive?

11 What type of motion does a lead screw commonly convert?

12 What feature distinguishes a ball screw from a conventional lead screw?

13 What is the main function of a bearing?

14 Which bearing uses balls between inner and outer rings?

15 What is the purpose of a coupling in a robot mechanism?

16 Which type of coupling can accommodate small shaft misalignments?

17 What is a robot end-effector?

18 Which gripper is suitable for lifting ferromagnetic metal parts?

19 Which gripper uses suction to hold an object?

20 Which property is especially useful for a robot arm material?

21 A robot arm has two revolute joints for planar motion and one prismatic joint for vertical motion. Assuming all joints are independently actuated, how many degrees of freedom does the arm have?

22 A robot wrist must provide independent pitch and yaw rotations about axes intersecting at one point, but it does not require roll. Which joint is most suitable?

23 A planar four-bar linkage has four links, including the fixed link, and four lower-pair joints. Using , what is its mobility?

24 Compared with a serial kinematic chain, why might a closed-loop parallel chain be selected for a pick-and-place robot?

25 A motor produces of torque and drives a reduction system with an efficiency of . What output torque is available?

26 A 20-tooth external gear rotating at drives a 60-tooth gear. What is the speed and direction of the driven gear?

27 In a compound train, a 15-tooth gear A drives a 45-tooth gear B. Gear B shares a shaft with a 20-tooth gear C, which drives a 40-tooth gear D. If A rotates at , what is the speed of D?

28 A driving pulley rotates at and drives a pulley using a belt. Neglecting slip, what is the driven speed?

29 A robot conveyor must maintain an exact speed ratio while transmitting relatively high torque in a dusty environment. Which drive is the better choice?

30 A single-start lead screw has a pitch of and rotates at . What is the ideal linear speed of the nut?

31 A fast vertical robot axis requires high positioning efficiency but must not fall when electrical power is removed. Which solution is most appropriate?

32 A high-speed robot joint shaft experiences radial load and axial load in both directions. Which bearing arrangement is most suitable?

33 A compact robot joint must resist radial force, axial force, and a large overturning moment using one bearing assembly. Which bearing is most suitable?

34 A servo motor must be connected to a ball screw with high torsional rigidity, negligible backlash, and tolerance for slight angular misalignment. Which coupling is most suitable?

35 A wrist supports a payload whose center is away and a end-effector whose center is away. Using and a safety factor of , what minimum static torque rating is required?

36 A two-jaw mechanical gripper lifts an object weighing . The friction coefficient at each jaw is , and a safety factor of is required. What minimum normal force must each jaw apply?

37 A vacuum gripper uses one circular suction cup of diameter with a pressure difference of . Ignoring leakage, what is the theoretical holding force?

38 Which workpiece is the most suitable for direct handling by a magnetic robot gripper?

39 A high-speed robot arm must have low moving mass while retaining high structural stiffness. Cost is less important than dynamic performance. Which material is the best choice?

40 A stationary robot base requires high rigidity and strong vibration damping, while low mass is not important. Which structural material is most suitable?

41 A planar kinematic chain has 8 links including the ground, 9 one-DOF lower pairs, and 1 higher pair. Assuming all constraints are independent, what is its mobility?

42 An ideal universal joint is modeled as two intersecting, mutually perpendicular revolute axes. What are the relative mobility and the number of independent instantaneous constraints between its input and output links?

43 For a planar 2R manipulator with nonzero link lengths and , the Jacobian determinant is . At which configurations does the end-effector lose instantaneous mobility in one Cartesian direction?

44 A motor gear with 20 teeth drives an 80-tooth load gear. The load inertia is , and gear inertias are negligible. What load inertia is reflected to the motor shaft?

45 A reduction stage has . A motor-side shaft of torsional stiffness is in series with a load-side shaft of stiffness . With an ideal rigid gear stage, what stiffness is seen at the motor?

46 Gear A with 18 teeth drives gear B with 54 teeth. B shares a shaft with gear C having 20 teeth, which drives gear D with 80 teeth. All meshes are external. What is the speed of D relative to A?

47 A simple planetary gear set has a 30-tooth sun and a 90-tooth ring. The ring is fixed, the sun is the input, and the carrier is the output. What is the carrier speed?

48 A belt driver of radius rotates at and drives a pulley of radius . If creep makes the actual driven speed 2% lower than the no-creep prediction, what is the driven speed?

49 A 15-tooth chain sprocket drives a 45-tooth sprocket at constant input speed. Neglecting elastic effects, which statement correctly describes chordal action?

50 A square-thread lead screw has mean diameter , lead , friction coefficient , and axial load . Ignoring collar friction, which result is correct?

51 A ball screw with lead and efficiency must produce a total axial force of . Neglecting rotational inertia, what motor torque is required?

52 A ball bearing has dynamic capacity . Under its specified load ratio, the catalog gives and . If and , what is its basic rating life ?

53 A long robot axis shaft undergoes significant thermal expansion. Which bearing arrangement best avoids thermally induced axial preload while maintaining precise radial and axial location at one end?

54 A precision servo axis requires high torsional stiffness, negligible backlash, and accommodation of small angular and axial misalignment. Which coupling is generally the best choice?

55 A tool origin is located at from the wrist origin, with parallel coordinate axes. At the tool, and . What torque is measured about the wrist origin?

56 A two-finger mechanical gripper holds a object by friction while accelerating upward at . Each finger applies the same normal force , the friction coefficient is , and a safety factor of 2 applies to the total required force. What minimum force must each finger apply?

57 A circular vacuum cup has diameter and operates at a pressure difference of . Surface leakage gives a derating factor of 0.70, and a safety factor of 2.5 is required. What is the allowable tensile load?

58 A magnetic gripper provides a derated normal holding force of . A vertical steel plate is supported only by friction with coefficient and accelerates upward at . With a safety factor of 2, what is the maximum plate mass?

59 Equal-length cantilever robot links have square cross-sections, equal mass, and identical end loading. Candidate properties are: aluminum , steel , titanium , and CFRP . Which material gives the least bending deflection?

60 A thin CFRP robot-link tube must carry axial bending, torsion, and hoop stresses while avoiding extension-shear and bending-extension coupling. Which laminate concept is most appropriate?